diff --git a/apps/api/migrations/038_media_assets.sql b/apps/api/migrations/038_media_assets.sql
new file mode 100644
index 0000000..02b7c3b
--- /dev/null
+++ b/apps/api/migrations/038_media_assets.sql
@@ -0,0 +1,28 @@
+-- 038: media assets for publishing (media attachments backend).
+--
+-- Owner need: posts need images/video, not text alone. This is the asset
+-- spine the draft's mediaAssetIds point at — one row per uploaded file, the
+-- bytes themselves in object storage (envelope-encrypted, content-addressed)
+-- keyed by storage_key. Everything is per-workspace; the sha256 is the
+-- plaintext content hash the storage service computes, so a re-upload
+-- deduplicates the OBJECT but still gets its own row (different alt text,
+-- different post usage). created_by is SET NULL on user deletion: the asset
+-- outlives the account that uploaded it.
+
+CREATE TABLE media_assets (
+  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  workspace_id uuid NOT NULL REFERENCES workspaces (id) ON DELETE CASCADE,
+  storage_key text NOT NULL,
+  mime text NOT NULL,
+  size_bytes bigint NOT NULL CHECK (size_bytes > 0),
+  sha256 text NOT NULL,
+  alt_text text,
+  created_by uuid REFERENCES users (id) ON DELETE SET NULL,
+  created_at timestamptz NOT NULL DEFAULT now(),
+  UNIQUE (id, workspace_id)
+);
+
+CREATE POLICY tenant_isolation ON media_assets
+  USING (workspace_id = NULLIF(current_setting('app.workspace_id', true), '')::uuid);
+
+CREATE INDEX media_assets_workspace_created ON media_assets (workspace_id, created_at);
diff --git a/apps/api/migrations/039_producer.sql b/apps/api/migrations/039_producer.sql
new file mode 100644
index 0000000..09ce798
--- /dev/null
+++ b/apps/api/migrations/039_producer.sql
@@ -0,0 +1,43 @@
+-- 039: producer job intake — a producer can ask for a NEW asset derived from an
+-- existing one (burned-in lower thirds/logos/clock, an optional voiceover mix).
+--
+-- WHY COLUMNS AND NOT A NEW TABLE: video_processing_jobs (009) already models the
+-- per-asset work queue (state machine, progress, output_key, RLS, tenant-immutability
+-- triggers, workspace-scoped grants). Intake only needs to distinguish WHAT a queued
+-- row asks the media-worker to do and carry the request payload; that is two columns
+-- on the existing queue plus a nullable pointer to the row it produces. A second
+-- table would duplicate the state machine and the isolation policy for no gain.
+--
+--   kind             'probe'  — the 009 behaviour: ingest + ffprobe + no-op transcode.
+--                    'compose' — burn overlays (and optionally a logo PNG) over the source.
+--                    'mix'     — compose AND replace/duck the audio bed with a voiceover.
+--                    Default 'probe' keeps every existing row and INSERT (009 code path)
+--                    meaning exactly what it meant before this migration.
+--   input_json       the validated producer request ({...request, requestedBy}), only
+--                    ever written by the API after strict allowlist parsing; the worker
+--                    re-validates. NULL for probe rows.
+--   produced_asset_id the video_assets row the job writes when it finishes, so a
+--                    finished job points forward to its output.
+--   video_assets.derived_from  the SOURCE asset id of a produced row; NULL for ingested
+--                    uploads. Produced rows are ordinary video_assets rows, so they appear
+--                    in the library listing and inherit its tenant isolation unchanged.
+--
+-- The kind enum is CHECK-constrained so an undecodable row cannot exist.
+
+BEGIN;
+
+ALTER TABLE video_processing_jobs
+  ADD COLUMN kind text NOT NULL DEFAULT 'probe'
+    CHECK (kind IN ('probe', 'compose', 'mix')),
+  ADD COLUMN input_json jsonb,
+  ADD COLUMN produced_asset_id uuid;
+
+ALTER TABLE video_assets
+  ADD COLUMN derived_from uuid REFERENCES video_assets(id);
+
+-- Jobs that produce a derived asset are claimed by the media-worker by kind.
+CREATE INDEX video_processing_jobs_kind_queued
+  ON video_processing_jobs (kind, created_at DESC)
+  WHERE state = 'queued';
+
+COMMIT;
diff --git a/apps/api/src/app.module.ts b/apps/api/src/app.module.ts
index fdd953c..ee1dd29 100644
--- a/apps/api/src/app.module.ts
+++ b/apps/api/src/app.module.ts
@@ -42,9 +42,10 @@ import { CollectivesModule } from "./collectives/collectives.module.js";
 import { MatrixSsoModule } from "./matrix-sso/matrix-sso.module.js";
 import { OidcModule } from "./oidc/oidc.module.js";
 import { SubmissionsModule } from "./submissions/submissions.module.js";
+import { MediaModule } from "./media/media.module.js";
 
 @Module({
-  imports: [HealthModule, LiveMonitorModule, MediaControlModule, ProductionModule, RealtimeModule, LiveChatModule, LiveModule, VirtualChannelsModule, ChatgovModule, IntakeModule, GroupFilesModule, SettingsModule, CollectivesModule, MatrixSsoModule, OidcModule, SubmissionsModule],
+  imports: [HealthModule, LiveMonitorModule, MediaControlModule, ProductionModule, RealtimeModule, LiveChatModule, LiveModule, VirtualChannelsModule, ChatgovModule, IntakeModule, GroupFilesModule, SettingsModule, CollectivesModule, MatrixSsoModule, OidcModule, SubmissionsModule, MediaModule],
   controllers: [
     DemoController,
     PublishingController,
diff --git a/apps/api/src/media/media.controller.ts b/apps/api/src/media/media.controller.ts
new file mode 100644
index 0000000..072c045
--- /dev/null
+++ b/apps/api/src/media/media.controller.ts
@@ -0,0 +1,134 @@
+/**
+ * Media assets (posting attachments): the asset spine that
+ * `drafts.post.mediaAssetIds` points at.
+ *
+ *   POST /media                draft.create — multipart `file` (optional
+ *                              `altText` text field), magic-byte sniffed
+ *                              (jpeg/png/webp, mp4/webm), capped 10 MiB image /
+ *                              64 MiB video, stored through the shared
+ *                              envelope-encrypted object storage, one
+ *                              media_assets row + `media.uploaded` audit
+ *   GET  /media/:id            draft.view — same-origin proxy of the bytes
+ *                              (never a redirect to S3), ETag + immutable cache
+ *
+ * The upload reuses the submissions/branding conventions: the declared
+ * content type is never trusted, only the magic bytes decide; the storage
+ * service content-addresses and envelope-encrypts; the row keeps the
+ * plaintext sha256 the storage layer computed.
+ */
+
+import {
+  BadRequestException,
+  Body,
+  Controller,
+  ForbiddenException,
+  Get,
+  HttpCode,
+  Inject,
+  Param,
+  Post,
+  Req,
+  Res,
+  UploadedFile,
+  UseGuards,
+  UseInterceptors,
+} from "@nestjs/common";
+import { FileInterceptor } from "@nestjs/platform-express";
+import type { Request, Response } from "express";
+import { requireSession } from "../http/validation.js";
+import { RbacGuard, RequirePermission, type AuthenticatedRequest } from "../rbac/rbac.guard.js";
+import { MediaService, MEDIA_MAX_VIDEO_BYTES, mediaAssetPath } from "./media.service.js";
+
+interface UploadFile {
+  buffer: Buffer;
+  mimetype?: string;
+}
+
+/** Bounds the buffered multipart request; MediaService re-checks after sniffing. */
+const FILE_LIMITS = {
+  fileSize: MEDIA_MAX_VIDEO_BYTES,
+  files: 1,
+  fields: 2,
+  fieldSize: 2048,
+  parts: 4,
+};
+
+export interface MediaUploadResult {
+  id: string;
+  url: string;
+}
+
+@Controller("media")
+@UseGuards(RbacGuard)
+export class MediaController {
+  constructor(@Inject(MediaService) private readonly media: MediaService) {}
+
+  @Post()
+  @HttpCode(200)
+  @RequirePermission("draft.create")
+  @UseInterceptors(FileInterceptor("file", { limits: FILE_LIMITS }))
+  async upload(
+    @Req() request: Request & AuthenticatedRequest,
+    @UploadedFile() file?: UploadFile,
+    @Body() body?: Record<string, unknown>,
+  ): Promise<MediaUploadResult> {
+    const session = requireSession(request);
+    if (file?.buffer === undefined || file.buffer.length === 0) {
+      throw new BadRequestException("a file is required (field: file)");
+    }
+    const altText = optionalAltText(body?.altText);
+    const asset = await this.media.upload(session.workspaceId, {
+      bytes: file.buffer,
+      declaredMime: typeof file.mimetype === "string" ? file.mimetype : "",
+      ...(altText === undefined ? {} : { altText }),
+      actor: { userId: session.userId, role: session.role },
+    });
+    return { id: asset.id, url: mediaAssetPath(asset.id) };
+  }
+
+  /**
+   * Same-origin asset read (the branding/video-thumbnail pattern): the API
+   * proxies the decrypted bytes from its own origin — an encrypted S3 object
+   * is never redirected to — with a bounded immutable cache, nosniff and an
+   * ETag for conditional revalidation.
+   */
+  @Get(":id")
+  @RequirePermission("draft.view")
+  async asset(
+    @Param("id") id: string,
+    @Req() request: Request & AuthenticatedRequest,
+    @Res({ passthrough: true }) response: Response,
+  ): Promise<void> {
+    const session = requireSession(request);
+    if (!/^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i.test(id)) {
+      throw new BadRequestException("id must be a UUID");
+    }
+    const origin = request.headers.origin;
+    const ownOrigin = process.env.PUBLIC_ORIGIN ?? `${request.protocol}://${request.get("host")}`;
+    if (origin !== undefined && origin !== ownOrigin) {
+      throw new ForbiddenException("cross-origin media asset denied");
+    }
+    const asset = await this.media.readAsset(session.workspaceId, id);
+    const etag = `"${asset.sha256}"`;
+    response.setHeader("ETag", etag);
+    response.setHeader("Cache-Control", "private, max-age=86400, immutable");
+    response.setHeader("Cross-Origin-Resource-Policy", "same-origin");
+    response.setHeader("X-Content-Type-Options", "nosniff");
+    const match = request.headers["if-none-match"];
+    if (match === etag || match === "*" || (typeof match === "string" && match.split(/,\s*/).includes(etag))) {
+      response.status(304).end();
+      return;
+    }
+    response.type(asset.mime).send(asset.bytes);
+  }
+}
+
+/** Optional free-text alt; empty/whitespace means "no alt text". */
+function optionalAltText(value: unknown): string | undefined {
+  if (value === undefined || value === null) return undefined;
+  if (typeof value !== "string") throw new BadRequestException("altText must be a string");
+  const trimmed = value.trim();
+  if (trimmed === "") return undefined;
+  if (trimmed.length > 1000) throw new BadRequestException("altText must be at most 1000 characters");
+  return trimmed;
+}
diff --git a/apps/api/src/media/media.module.ts b/apps/api/src/media/media.module.ts
new file mode 100644
index 0000000..4cbacc4
--- /dev/null
+++ b/apps/api/src/media/media.module.ts
@@ -0,0 +1,17 @@
+import { Module } from "@nestjs/common";
+import { MediaController } from "./media.controller.js";
+import { MediaService } from "./media.service.js";
+
+/**
+ * Media attachments for publishing: POST /media (draft.create) uploads a
+ * sniffed, capped attachment into the shared encrypted object storage and
+ * records a media_assets row; GET /media/:id (draft.view) proxies the bytes
+ * same-origin. Everything mutates through MediaService, which keeps the row
+ * write and the `media.uploaded` tenant audit event together.
+ */
+@Module({
+  controllers: [MediaController],
+  providers: [MediaService],
+  exports: [MediaService],
+})
+export class MediaModule {}
diff --git a/apps/api/src/media/media.service.ts b/apps/api/src/media/media.service.ts
new file mode 100644
index 0000000..871d00d
--- /dev/null
+++ b/apps/api/src/media/media.service.ts
@@ -0,0 +1,203 @@
+/**
+ * Media assets for publishing: upload (magic-byte sniffed, capped), row
+ * insertion with a tenant audit event, and the auth-scoped read the
+ * `/media/:id` route proxies.
+ *
+ * Deliberately mirrors the submissions/branding seams:
+ *   * the declared content type is never trusted — sniffMedia decides;
+ *   * the size cap is re-checked AFTER sniffing, because the cap depends on
+ *     the sniffed kind (image 10 MiB, video 64 MiB);
+ *   * storage is the shared envelope-encrypted, content-addressed S3 path;
+ *   * the row keeps the plaintext sha256 storage computed, so a later read
+ *     can serve a strong ETag and the draft can cross-check the asset.
+ */
+
+import { BadRequestException, Inject, Injectable, NotFoundException, Optional, ServiceUnavailableException } from "@nestjs/common";
+import { appendTenantAudit } from "../audit/audit.service.js";
+import { withTenant } from "../db/client.js";
+import { S3Storage, s3ConfigFromEnv, sha256, type StorageService } from "../storage/storage.js";
+
+/** Images are small; video costs real bytes. Both are hard caps. */
+export const MEDIA_MAX_IMAGE_BYTES = 10 * 1024 * 1024;
+export const MEDIA_MAX_VIDEO_BYTES = 64 * 1024 * 1024;
+
+/** Provider-compatible ceiling: a post carries at most 4 attachments. */
+export const MAX_MEDIA_PER_POST = 4;
+
+export type MediaKind = "image" | "video";
+
+export interface SniffedMedia {
+  kind: MediaKind;
+  mime: string;
+}
+
+/** URL path of the auth-scoped read route for a media asset. */
+export function mediaAssetPath(id: string): string {
+  return `/media/${id}`;
+}
+
+/**
+ * Magic-byte sniffing for the five posting attachment types. Order matters
+ * only for readability — every signature is disjoint.
+ */
+export function sniffMediaAsset(bytes: Buffer): SniffedMedia | null {
+  if (bytes.length < 16) return null;
+  // png: 89 50 4E 47 0D 0A 1A 0A
+  if (bytes.subarray(0, 8).toString("hex") === "89504e470d0a1a0a") return { kind: "image", mime: "image/png" };
+  // jpeg: FF D8 FF
+  if (bytes[0] === 0xff && bytes[1] === 0xd8 && bytes[2] === 0xff) return { kind: "image", mime: "image/jpeg" };
+  // webp: "RIFF"...."WEBP"
+  if (bytes.subarray(0, 4).toString("latin1") === "RIFF" && bytes.subarray(8, 12).toString("latin1") === "WEBP") {
+    return { kind: "image", mime: "image/webp" };
+  }
+  // mp4: "ftyp" at offset 4
+  if (bytes.subarray(4, 8).toString("latin1") === "ftyp") return { kind: "video", mime: "video/mp4" };
+  // webm/mkv: EBML magic 1A 45 DF A3
+  if (bytes.subarray(0, 4).toString("hex") === "1a45dfa3") return { kind: "video", mime: "video/webm" };
+  return null;
+}
+
+export function mediaCapFor(kind: MediaKind): number {
+  return kind === "video" ? MEDIA_MAX_VIDEO_BYTES : MEDIA_MAX_IMAGE_BYTES;
+}
+
+export interface MediaAssetRecord {
+  id: string;
+  workspaceId: string;
+  storageKey: string;
+  mime: string;
+  kind: MediaKind;
+  sizeBytes: number;
+  sha256: string;
+  altText: string | null;
+  createdAt: Date;
+}
+
+export interface MediaActor {
+  userId: string;
+  role: string;
+}
+
+export interface MediaDependencies {
+  storage: StorageService;
+}
+
+export const MEDIA_DEPENDENCIES = Symbol("MEDIA_DEPENDENCIES");
+
+interface MediaRow {
+  id: string;
+  workspace_id: string;
+  storage_key: string;
+  mime: string;
+  size_bytes: string | number;
+  sha256: string;
+  alt_text: string | null;
+  created_by: string | null;
+  created_at: Date;
+}
+
+function kindForMime(mime: string): MediaKind {
+  return mime.startsWith("video/") ? "video" : "image";
+}
+
+function fromRow(row: MediaRow): MediaAssetRecord {
+  return {
+    id: row.id,
+    workspaceId: row.workspace_id,
+    storageKey: row.storage_key,
+    mime: row.mime,
+    kind: kindForMime(row.mime),
+    sizeBytes: Number(row.size_bytes),
+    sha256: row.sha256,
+    altText: row.alt_text,
+    createdAt: new Date(row.created_at),
+  };
+}
+
+@Injectable()
+export class MediaService {
+  private readonly storage: StorageService;
+
+  constructor(@Optional() @Inject(MEDIA_DEPENDENCIES) deps?: Partial<MediaDependencies>) {
+    // Same lazy-construction decision as SubmissionsService.requireStorage:
+    // tests inject a stub, production constructs from env once.
+    this.storage = deps?.storage ?? new S3Storage(s3ConfigFromEnv());
+  }
+
+  /** Upload one attachment: sniff → cap → store → row + audit. */
+  async upload(workspaceId: string, input: {
+    bytes: Buffer;
+    declaredMime: string;
+    altText?: string;
+    actor: MediaActor;
+  }): Promise<MediaAssetRecord> {
+    const sniffed = sniffMediaAsset(input.bytes);
+    if (sniffed === null) {
+      throw new BadRequestException("unrecognised file type — expected jpeg/png/webp image or mp4/webm video");
+    }
+    const max = mediaCapFor(sniffed.kind);
+    if (input.bytes.length === 0 || input.bytes.length > max) {
+      throw new BadRequestException(`file must be 1 byte to ${max} bytes for a ${sniffed.kind}`);
+    }
+    if (input.declaredMime !== "" && input.declaredMime !== sniffed.mime) {
+      throw new BadRequestException("file content does not match the declared type");
+    }
+    const stored = await this.storage.putContent(input.bytes, sniffed.mime).catch(() => {
+      throw new ServiceUnavailableException("media storage unavailable — try again later");
+    });
+    const digest = sha256(input.bytes);
+    const record = await withTenant(workspaceId, async (client) => {
+      const inserted = await client.query<MediaRow>(
+        `INSERT INTO media_assets (workspace_id, storage_key, mime, size_bytes, sha256, alt_text, created_by)
+         VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING *`,
+        [workspaceId, stored.key, sniffed.mime, stored.sizeBytes, digest, input.altText ?? null, input.actor.userId],
+      );
+      const row = inserted.rows[0];
+      if (row === undefined) throw new Error("media asset insert returned no row");
+      return fromRow(row);
+    });
+    await appendTenantAudit(workspaceId, {
+      actorUserId: input.actor.userId,
+      actorRole: input.actor.role,
+      action: "media.uploaded",
+      targetType: "media_asset",
+      targetId: record.id,
+      diff: { kind: sniffed.kind, mime: sniffed.mime, sizeBytes: input.bytes.length, ...(input.altText !== undefined ? { altText: input.altText } : {}) },
+    });
+    return record;
+  }
+
+  /** Auth-scoped read: RLS already fences this to the caller's workspace. */
+  async readAsset(workspaceId: string, id: string): Promise<MediaAssetRecord & { bytes: Buffer }> {
+    const asset = await withTenant(workspaceId, async (client) => {
+      const result = await client.query<MediaRow>("SELECT * FROM media_assets WHERE id = $1", [id]);
+      const row = result.rows[0];
+      if (row === undefined) throw new NotFoundException(`media asset ${id} not found`);
+      return fromRow(row);
+    });
+    const bytes = await this.storage.getObject(asset.storageKey).catch(() => {
+      throw new ServiceUnavailableException("media asset unavailable");
+    });
+    return { ...asset, bytes };
+  }
+
+  /**
+   * Draft-side existence check: every mediaAssetId the caller sent must be a
+   * row in THIS workspace. Runs inside the draft's tenant transaction, so the
+   * RLS policy is the fence — a foreign tenant's id simply counts as absent.
+   */
+  static async assertAssetsExist(
+    client: { query: (sql: string, values: unknown[]) => Promise<{ rows: Array<{ count: string | number }> }> },
+    mediaAssetIds: string[],
+  ): Promise<void> {
+    if (mediaAssetIds.length === 0) return;
+    const result = await client.query(
+      "SELECT count(*)::integer AS count FROM media_assets WHERE id = ANY($1::uuid[])",
+      [mediaAssetIds],
+    );
+    const count = Number(result.rows[0]?.count ?? 0);
+    if (count !== mediaAssetIds.length) {
+      throw new BadRequestException("one or more mediaAssetIds do not exist in this workspace");
+    }
+  }
+}
diff --git a/apps/api/src/media/media.test.ts b/apps/api/src/media/media.test.ts
new file mode 100644
index 0000000..98226c3
--- /dev/null
+++ b/apps/api/src/media/media.test.ts
@@ -0,0 +1,312 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { BadRequestException, ServiceUnavailableException } from "@nestjs/common";
+import type { PoolClient } from "pg";
+import {
+  MEDIA_MAX_IMAGE_BYTES,
+  MEDIA_MAX_VIDEO_BYTES,
+  MAX_MEDIA_PER_POST,
+  MediaService,
+  mediaAssetPath,
+  sniffMediaAsset,
+} from "./media.service.js";
+import { appendTenantAudit } from "../audit/audit.service.js";
+import { sha256, type StorageService } from "../storage/storage.js";
+import { MediaController } from "./media.controller.js";
+import type { AuthenticatedRequest } from "../rbac/rbac.guard.js";
+import type { Request, Response } from "express";
+
+/**
+ * Unit level: sniffing, per-kind caps, declared-mime cross-check, the
+ * storage->row->audit contract — with the DB and S3 faked. Live-DB coverage
+ * (RLS tenant isolation, migration shape) is the integration suite's job.
+ */
+
+const dbMock = vi.hoisted(() => ({ withTenant: vi.fn() }));
+vi.mock("../db/client.js", () => ({ withTenant: dbMock.withTenant }));
+vi.mock("../audit/audit.service.js", () => ({ appendTenantAudit: vi.fn(async () => "audit-id") }));
+
+const WS = "0d9a1b40-6f0f-4b1e-8f0e-3f3c9e6b4a10";
+const USER = "8f7f6e50-7b0f-4a2e-9d3e-2f2d1a0c5b21";
+const ACTOR = { userId: USER, role: "Owner" };
+
+const PNG = Buffer.concat([
+  Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]),
+  Buffer.alloc(24, 0x11),
+]);
+const JPEG = Buffer.concat([Buffer.from([0xff, 0xd8, 0xff]), Buffer.alloc(24, 0x22)]);
+const WEBP = Buffer.concat([
+  Buffer.from("RIFF", "latin1"),
+  Buffer.from([0x24, 0x00, 0x00, 0x00]),
+  Buffer.from("WEBP", "latin1"),
+  Buffer.alloc(16, 0x33),
+]);
+const MP4 = Buffer.concat([
+  Buffer.alloc(4, 0x00),
+  Buffer.from("ftyp", "latin1"),
+  Buffer.from("isom", "latin1"),
+  Buffer.alloc(24, 0x44),
+]);
+const WEBM = Buffer.concat([Buffer.from([0x1a, 0x45, 0xdf, 0xa3]), Buffer.alloc(24, 0x55)]);
+
+function fakeStorage(): StorageService & {
+  putContent: ReturnType<typeof vi.fn>;
+  getObject: ReturnType<typeof vi.fn>;
+} {
+  return {
+    putContent: vi.fn(async (bytes: Buffer, contentType: string) => {
+      const hash = sha256(bytes);
+      return {
+        key: `sha256/${hash}.${contentType === "image/jpeg" ? "jpg" : contentType.split("/")[1]}`,
+        hash,
+        sizeBytes: bytes.length,
+        contentType,
+        deduplicated: false,
+      };
+    }),
+    getObject: vi.fn(async () => {
+      throw new Error("missing");
+    }),
+    hasContent: vi.fn(async () => false),
+    presign: vi.fn(async () => ""),
+  };
+}
+
+/** withTenant fake: records the insert and hands back the row it would store. */
+function tenantInsertReturningRow() {
+  const inserts: unknown[][] = [];
+  dbMock.withTenant.mockImplementation(async (_ws: string, fn: (client: PoolClient) => Promise<unknown>) =>
+    fn({
+      query: async (sql: string, values?: unknown[]) => {
+        if (sql.startsWith("INSERT INTO media_assets")) {
+          inserts.push(values ?? []);
+          const [workspaceId, storageKey, mime, sizeBytes, digest, altText, createdBy] = values as unknown[];
+          return {
+            rows: [{
+              id: "11111111-2222-4333-8444-555555555555",
+              workspace_id: workspaceId,
+              storage_key: storageKey,
+              mime,
+              size_bytes: sizeBytes,
+              sha256: digest,
+              alt_text: altText,
+              created_by: createdBy,
+              created_at: new Date("2026-01-02T03:04:05Z"),
+            }],
+          };
+        }
+        throw new Error(`unexpected query: ${sql}`);
+      },
+    } as unknown as PoolClient),
+  );
+  return inserts;
+}
+
+beforeEach(() => {
+  dbMock.withTenant.mockReset();
+  vi.mocked(appendTenantAudit).mockClear();
+});
+
+describe("sniffMediaAsset", () => {
+  it("recognises the two video and three image types by magic bytes", () => {
+    expect(sniffMediaAsset(PNG)).toEqual({ kind: "image", mime: "image/png" });
+    expect(sniffMediaAsset(JPEG)).toEqual({ kind: "image", mime: "image/jpeg" });
+    expect(sniffMediaAsset(WEBP)).toEqual({ kind: "image", mime: "image/webp" });
+    expect(sniffMediaAsset(MP4)).toEqual({ kind: "video", mime: "video/mp4" });
+    expect(sniffMediaAsset(WEBM)).toEqual({ kind: "video", mime: "video/webm" });
+  });
+
+  it("rejects anything else — including a lying content type", () => {
+    expect(sniffMediaAsset(Buffer.from("definitely not media at all, sorry", "utf8"))).toBeNull();
+    expect(sniffMediaAsset(Buffer.alloc(8, 0x00))).toBeNull();
+    // too short to sniff
+    expect(sniffMediaAsset(Buffer.from([0x89, 0x50]))).toBeNull();
+  });
+});
+
+describe("caps", () => {
+  it("image cap is 10 MiB and video cap is 64 MiB", () => {
+    expect(MEDIA_MAX_IMAGE_BYTES).toBe(10 * 1024 * 1024);
+    expect(MEDIA_MAX_VIDEO_BYTES).toBe(64 * 1024 * 1024);
+    expect(MAX_MEDIA_PER_POST).toBe(4);
+  });
+
+  it("refuses an image over the image cap even though it fits the video cap", async () => {
+    const storage = fakeStorage();
+    const media = new MediaService({ storage });
+    const oversized = Buffer.concat([PNG.subarray(0, 8), Buffer.alloc(MEDIA_MAX_IMAGE_BYTES + 1, 0x00)]);
+    await expect(media.upload(WS, { bytes: oversized, declaredMime: "", actor: ACTOR }))
+      .rejects.toThrow(BadRequestException);
+    expect(storage.putContent).not.toHaveBeenCalled();
+  });
+
+  it("refuses a video over the video cap", async () => {
+    const storage = fakeStorage();
+    const media = new MediaService({ storage });
+    const oversized = Buffer.concat([MP4, Buffer.alloc(MEDIA_MAX_VIDEO_BYTES + 1, 0x00)]);
+    await expect(media.upload(WS, { bytes: oversized, declaredMime: "", actor: ACTOR }))
+      .rejects.toThrow(BadRequestException);
+    expect(storage.putContent).not.toHaveBeenCalled();
+  });
+
+  it("accepts a video larger than the image cap (kind-dependent limit)", async () => {
+    const storage = fakeStorage();
+    const media = new MediaService({ storage });
+    tenantInsertReturningRow();
+    const bytes = Buffer.concat([MP4, Buffer.alloc(MEDIA_MAX_IMAGE_BYTES + 1024, 0x00)]);
+    const asset = await media.upload(WS, { bytes, declaredMime: "", actor: ACTOR });
+    expect(asset.kind).toBe("video");
+    expect(asset.sizeBytes).toBe(bytes.length);
+    expect(storage.putContent).toHaveBeenCalledWith(bytes, "video/mp4");
+  });
+});
+
+describe("MediaService.upload", () => {
+  it("sniffs, stores through putContent, inserts the row and audits media.uploaded", async () => {
+    const storage = fakeStorage();
+    const media = new MediaService({ storage });
+    const inserts = tenantInsertReturningRow();
+    const asset = await media.upload(WS, { bytes: PNG, declaredMime: "image/png", altText: "a crowd", actor: ACTOR });
+
+    expect(asset.mime).toBe("image/png");
+    expect(asset.kind).toBe("image");
+    expect(asset.sha256).toBe(sha256(PNG));
+    expect(asset.altText).toBe("a crowd");
+    expect(mediaAssetPath(asset.id)).toBe(`/media/${asset.id}`);
+    expect(storage.putContent).toHaveBeenCalledTimes(1);
+    expect(storage.putContent).toHaveBeenCalledWith(PNG, "image/png");
+    expect(inserts).toHaveLength(1);
+    expect(inserts[0]).toEqual([WS, `sha256/${sha256(PNG)}.png`, "image/png", PNG.length, sha256(PNG), "a crowd", USER]);
+    expect(appendTenantAudit).toHaveBeenCalledWith(WS, expect.objectContaining({
+      actorUserId: USER,
+      action: "media.uploaded",
+      targetType: "media_asset",
+      targetId: asset.id,
+    }));
+  });
+
+  it("rejects a declared type that contradicts the sniffed bytes", async () => {
+    const storage = fakeStorage();
+    const media = new MediaService({ storage });
+    await expect(media.upload(WS, { bytes: PNG, declaredMime: "video/mp4", actor: ACTOR }))
+      .rejects.toThrow("file content does not match the declared type");
+    expect(storage.putContent).not.toHaveBeenCalled();
+    expect(appendTenantAudit).not.toHaveBeenCalled();
+  });
+
+  it("rejects an unrecognised file before touching storage", async () => {
+    const storage = fakeStorage();
+    const media = new MediaService({ storage });
+    await expect(media.upload(WS, { bytes: Buffer.alloc(64, 0x41), declaredMime: "image/png", actor: ACTOR }))
+      .rejects.toThrow(BadRequestException);
+    expect(storage.putContent).not.toHaveBeenCalled();
+  });
+
+  it("surfaces a storage failure as 503 without leaving a row", async () => {
+    const storage = fakeStorage();
+    storage.putContent.mockRejectedValueOnce(new Error("ECONNREFUSED"));
+    const media = new MediaService({ storage });
+    await expect(media.upload(WS, { bytes: JPEG, declaredMime: "", actor: ACTOR }))
+      .rejects.toThrow(ServiceUnavailableException);
+    expect(dbMock.withTenant).not.toHaveBeenCalled();
+  });
+});
+
+describe("MediaController", () => {
+  const session = { workspaceId: WS, userId: USER, role: "Owner" };
+
+  function requestWith(overrides: Partial<Request> = {}): Request & AuthenticatedRequest {
+    return {
+      headers: {} as Record<string, string | string[] | undefined>,
+      protocol: "http",
+      get: (name: string) => (name === "host" ? "api.test" : undefined),
+      session,
+      ...overrides,
+    } as unknown as Request & AuthenticatedRequest;
+  }
+
+  function responseRecording(): { response: Response; headers: Record<string, unknown>; body: unknown[]; status: number[] } {
+    const headers: Record<string, unknown> = {};
+    const body: unknown[] = [];
+    const status: number[] = [];
+    const response = {
+      setHeader: (k: string, v: unknown) => { headers[k.toLowerCase()] = v; },
+      status: (code: number) => { status.push(code); return response; },
+      type: () => response,
+      send: (payload: unknown) => { body.push(payload); return response; },
+      end: () => { body.push(undefined); return response; },
+    } as unknown as Response;
+    return { response, headers, body, status };
+  }
+
+  it("rejects a missing upload file", async () => {
+    const controller = new MediaController(new MediaService({ storage: fakeStorage() }));
+    await expect(controller.upload(requestWith(), undefined, {})).rejects.toThrow("a file is required");
+  });
+
+  it("returns the asset id and its /media/<id> url", async () => {
+    const storage = fakeStorage();
+    tenantInsertReturningRow();
+    const controller = new MediaController(new MediaService({ storage }));
+    const result = await controller.upload(requestWith(), { buffer: WEBP, mimetype: "image/webp" }, {});
+    expect(result.url).toBe(`/media/${result.id}`);
+    expect(result.id).toBe("11111111-2222-4333-8444-555555555555");
+  });
+
+  it("serves bytes with an ETag, cache and nosniff headers", async () => {
+    const storage = fakeStorage();
+    storage.getObject.mockResolvedValue(PNG);
+    dbMock.withTenant.mockImplementation(async (_ws: string, fn: (client: PoolClient) => Promise<unknown>) =>
+      fn({
+        query: async () => ({
+          rows: [{
+            id: "11111111-2222-4333-8444-555555555555", workspace_id: WS,
+            storage_key: `sha256/${sha256(PNG)}.png`, mime: "image/png", size_bytes: PNG.length,
+            sha256: sha256(PNG), alt_text: null, created_by: USER, created_at: new Date(),
+          }],
+        }),
+      } as unknown as PoolClient));
+    const controller = new MediaController(new MediaService({ storage }));
+    const { response, headers, body } = responseRecording();
+    await controller.asset("11111111-2222-4333-8444-555555555555", requestWith(), response);
+    expect(headers.etag).toBe(`"${sha256(PNG)}"`);
+    expect(String(headers["cache-control"])).toContain("immutable");
+    expect(headers["x-content-type-options"]).toBe("nosniff");
+    expect(body[0]).toBe(PNG);
+  });
+
+  it("answers a matching If-None-Match with 304 and no body", async () => {
+    const storage = fakeStorage();
+    storage.getObject.mockResolvedValue(JPEG);
+    dbMock.withTenant.mockImplementation(async (_ws: string, fn: (client: PoolClient) => Promise<unknown>) =>
+      fn({ query: async () => ({ rows: [{ id: "x", workspace_id: WS, storage_key: "k", mime: "image/jpeg", size_bytes: 1, sha256: sha256(JPEG), alt_text: null, created_by: null, created_at: new Date() }] }) } as unknown as PoolClient));
+    const controller = new MediaController(new MediaService({ storage }));
+    const { response, status, body } = responseRecording();
+    await controller.asset("11111111-2222-4333-8444-555555555555",
+      requestWith({ headers: { "if-none-match": `"${sha256(JPEG)}"` } }), response);
+    expect(status).toContain(304);
+    // 304 carries no body (end() pushes a single undefined entry).
+    expect(body).toEqual([undefined]);
+    // A mismatching ETag still sends the bytes.
+    const second = responseRecording();
+    await controller.asset("11111111-2222-4333-8444-555555555555",
+      requestWith({ headers: { "if-none-match": '"stale"' } }), second.response);
+    expect(second.status).not.toContain(304);
+    expect(second.body[0]).toBe(JPEG);
+  });
+
+  it("refuses a cross-origin read", async () => {
+    const storage = fakeStorage();
+    const controller = new MediaController(new MediaService({ storage }));
+    const { response } = responseRecording();
+    await expect(controller.asset("11111111-2222-4333-8444-555555555555",
+      requestWith({ headers: { origin: "https://elsewhere.example" } }), response))
+      .rejects.toThrow("cross-origin media asset denied");
+    expect(storage.getObject).not.toHaveBeenCalled();
+  });
+
+  it("refuses a non-UUID asset id", async () => {
+    const controller = new MediaController(new MediaService({ storage: fakeStorage() }));
+    const { response } = responseRecording();
+    await expect(controller.asset("not-a-uuid", requestWith(), response)).rejects.toThrow("id must be a UUID");
+  });
+});
diff --git a/apps/api/src/publishing/publishing.controller.ts b/apps/api/src/publishing/publishing.controller.ts
index ca66e14..2d99603 100644
--- a/apps/api/src/publishing/publishing.controller.ts
+++ b/apps/api/src/publishing/publishing.controller.ts
@@ -17,6 +17,7 @@ import {
 import type { Request, Response } from "express";
 import { RbacGuard, RequireGroupAccess, RequirePermission, type AuthenticatedRequest } from "../rbac/rbac.guard.js";
 import { ApprovalGateService } from "./approval-gate.service.js";
+import { MAX_MEDIA_PER_POST } from "../media/media.service.js";
 import type { GateDecisionRecord } from "../chatgov/gate.service.js";
 import {
   PublishingService,
@@ -238,20 +239,19 @@ function parseCreateDraft(value: unknown): CreateDraftDto {
   const post = requireObject(body.post, "post");
   const text = requireString(post.text, "post.text");
   const visibility = requireVisibility(post.visibility);
-  if (!Array.isArray(post.mediaAssetIds) || !post.mediaAssetIds.every((id) => typeof id === "string")) {
-    throw new BadRequestException("post.mediaAssetIds must be an array of strings");
-  }
+  const mediaAssetIds = parseMediaAssetIds(post.mediaAssetIds);
+  const altTexts = parseAltTexts(post.altTexts, mediaAssetIds.length);
   const providerMetadata = requireObject(post.providerMetadata, "post.providerMetadata");
-  if (post.mediaAssetIds.length > 0) throw new BadRequestException("publishing currently supports text only");
   if (["idempotencyKey", "draftId", "mediaIds"].some((key) => key in providerMetadata)) throw new BadRequestException("post metadata contains reserved execution keys");
   if (Buffer.byteLength(JSON.stringify(providerMetadata)) > 16_384) throw new BadRequestException("post metadata is too large");
   if (post.scheduledAt !== undefined) requireTimestamp(post.scheduledAt, "post.scheduledAt");
   return {
     post: {
       text,
-      mediaAssetIds: post.mediaAssetIds,
+      mediaAssetIds,
       visibility,
       providerMetadata,
+      ...(altTexts === undefined ? {} : { altTexts }),
       ...(typeof post.scheduledAt === "string" ? { scheduledAt: post.scheduledAt } : {}),
     },
   };
@@ -322,6 +322,40 @@ function parseListLimit(value: string | undefined): number {
   return Math.min(n, 200);
 }
 
+/**
+ * 0..4 attachments, each a media_assets id. Existence in the caller's
+ * workspace is checked service-side (RLS-scoped) — here we only bound the
+ * shape, the count and the id syntax.
+ */
+function parseMediaAssetIds(value: unknown): string[] {
+  if (value === undefined) return [];
+  if (!Array.isArray(value) || !value.every((id) => typeof id === "string")) {
+    throw new BadRequestException("post.mediaAssetIds must be an array of strings");
+  }
+  if (value.length > MAX_MEDIA_PER_POST) {
+    throw new BadRequestException(`post.mediaAssetIds supports at most ${MAX_MEDIA_PER_POST} attachments`);
+  }
+  return value.map((id) => parseId(id));
+}
+
+/** Optional alt texts, positionally aligned with mediaAssetIds (null = none). */
+function parseAltTexts(value: unknown, mediaCount: number): (string | null)[] | undefined {
+  if (value === undefined) return undefined;
+  if (!Array.isArray(value) || !value.every((entry) => entry === null || typeof entry === "string")) {
+    throw new BadRequestException("post.altTexts must be an array of strings or nulls");
+  }
+  if (value.length !== mediaCount) {
+    throw new BadRequestException("post.altTexts must align with post.mediaAssetIds (same length)");
+  }
+  return value.map((entry) => {
+    if (entry === null || entry === undefined) return null;
+    const trimmed = entry.trim();
+    if (trimmed === "") return null;
+    if (trimmed.length > 1000) throw new BadRequestException("post.altTexts entries must be at most 1000 characters");
+    return trimmed;
+  });
+}
+
 function requireVisibility(value: unknown): DraftPost["visibility"] {
   if (
     value !== "public" &&
diff --git a/apps/api/src/publishing/publishing.service.ts b/apps/api/src/publishing/publishing.service.ts
index 1a2af6f..f32d8c1 100644
--- a/apps/api/src/publishing/publishing.service.ts
+++ b/apps/api/src/publishing/publishing.service.ts
@@ -22,7 +22,10 @@ export type DraftState = "editing" | "in_review" | "approved" | "rejected" | "sc
 
 export interface DraftPost {
   text: string;
+  /** media_assets ids (0..4); existence is checked against this workspace on write. */
   mediaAssetIds: string[];
+  /** Optional alt texts, positionally aligned with mediaAssetIds. */
+  altTexts?: (string | null)[];
   visibility: "public" | "unlisted" | "private" | "followers" | "provider_default";
   scheduledAt?: string;
   providerMetadata: Record<string, unknown>;
@@ -180,6 +183,9 @@ export class PublishingService {
     await this.dependencies.assertReady();
     const draft = await this.dependencies.tenantTransaction(workspaceId, async (client) => {
       await client.query("SELECT id FROM workspaces WHERE id = $1 FOR UPDATE", [workspaceId]);
+      // FK checks bypass RLS, so a foreign tenant's asset id would satisfy the
+      // constraint; this RLS-scoped count is the actual tenancy check.
+      await assertMediaAssetsExist(client, post.mediaAssetIds);
       const result = await client.query(
         `INSERT INTO drafts (workspace_id, author_user_id, post)
          VALUES ($1, $2, $3) RETURNING *`,
@@ -365,6 +371,7 @@ export class PublishingService {
     await this.dependencies.assertReady();
     const draft = await this.dependencies.tenantTransaction(workspaceId, async (client) => {
       await client.query("SELECT id FROM workspaces WHERE id = $1 FOR UPDATE", [workspaceId]);
+      await assertMediaAssetsExist(client, post.mediaAssetIds);
       const result = await client.query(
         `UPDATE drafts SET post = $2, updated_at = now()
          WHERE id = $1 AND (state = 'editing' OR (state = 'in_review' AND EXISTS (SELECT 1 FROM polls WHERE draft_id = $1 AND state = 'open'))) RETURNING *`,
@@ -639,6 +646,22 @@ export class PublishingService {
   }
 }
 
+/**
+ * Every mediaAssetId must be a media_assets row in THIS workspace. Runs inside
+ * the caller's tenant transaction so the RLS tenant_isolation policy is the
+ * fence -- a foreign tenant's id simply counts as absent.
+ */
+async function assertMediaAssetsExist(client: PoolClient, mediaAssetIds: string[]): Promise<void> {
+  if (mediaAssetIds.length === 0) return;
+  const result = await client.query<{ count: string | number }>(
+    "SELECT count(*)::integer AS count FROM media_assets WHERE id = ANY($1::uuid[])",
+    [mediaAssetIds],
+  );
+  if (Number(result.rows[0]?.count ?? 0) !== mediaAssetIds.length) {
+    throw new BadRequestException("one or more post.mediaAssetIds do not exist in this workspace");
+  }
+}
+
 function requiredRow(row: unknown, description: string): Record<string, unknown> {
   if (typeof row !== "object" || row === null) throw new Error(`database did not return ${description}`);
   return row as Record<string, unknown>;
diff --git a/apps/api/src/video/produce-request.test.ts b/apps/api/src/video/produce-request.test.ts
new file mode 100644
index 0000000..cea4ec1
--- /dev/null
+++ b/apps/api/src/video/produce-request.test.ts
@@ -0,0 +1,143 @@
+import { describe, expect, it } from "vitest";
+import {
+  MAX_PRODUCE_OVERLAY_TEXT,
+  MAX_PRODUCE_POSITION,
+  parseProduceRequest,
+} from "./produce-request.js";
+
+const voiceoverAssetId = "20000000-0000-4000-8000-000000000002";
+
+describe("produce request validation", () => {
+  it("accepts a full request and canonicalizes it (fixed key order, defaults dropped)", () => {
+    const parsed = parseProduceRequest({
+      overlays: [
+        { kind: "lower_third", text: "Live from the occupation", position: { x: 0, y: 100 } },
+        { kind: "logo", logoStorageKey: "sha256/9f2b1c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d.png", position: { x: 100, y: 0 } },
+        { kind: "clock" },
+      ],
+      voiceover: { assetId: voiceoverAssetId, gainDb: -6, duckOriginal: true },
+      outputLabel: "Riot recap v2",
+      lane: "remote",
+    });
+    expect(parsed).toEqual({
+      overlays: [
+        { kind: "lower_third", text: "Live from the occupation", position: { x: 0, y: 100 } },
+        { kind: "logo", logoStorageKey: "sha256/9f2b1c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d.png", position: { x: 100, y: 0 } },
+        { kind: "clock", position: undefined },
+      ],
+      voiceover: { assetId: voiceoverAssetId, gainDb: -6, duckOriginal: true },
+      outputLabel: "Riot recap v2",
+      lane: "remote",
+    });
+    // Same input always serializes to the same input_json bytes.
+    expect(JSON.stringify(parsed)).toBe(JSON.stringify(parseProduceRequest(JSON.parse(JSON.stringify({
+      lane: "remote",
+      outputLabel: "Riot recap v2",
+      voiceover: { duckOriginal: true, gainDb: -6, assetId: voiceoverAssetId },
+      overlays: [
+        { position: { y: 100, x: 0 }, text: "Live from the occupation", kind: "lower_third" },
+        { position: { y: 0, x: 100 }, logoStorageKey: "sha256/9f2b1c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d.png", kind: "logo" },
+        { kind: "clock" },
+      ],
+    })))));
+  });
+
+  it("accepts an empty body and treats every field as optional", () => {
+    expect(parseProduceRequest({})).toEqual({});
+    expect(parseProduceRequest({ overlays: null, voiceover: null, outputLabel: null, lane: null })).toEqual({});
+  });
+
+  it("rejects an unknown key on the body, an overlay and a voiceover (never ignores one)", () => {
+    expect(() => parseProduceRequest({ outputLabel: "x", filter: "drawtext" })).toThrow(/body\.filter is not allowed/);
+    expect(() => parseProduceRequest({ apiKey: "x" })).toThrow(/secrets are never accepted/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", layer: 0 }] })).toThrow(/overlays\[0\]\.layer is not allowed/);
+    expect(() => parseProduceRequest({ voiceover: { assetId: voiceoverAssetId, streamKey: "x" } })).toThrow(/secrets are never accepted/);
+  });
+
+  it("rejects filtergraph and shell metacharacters in overlay text", () => {
+    for (const hostile of [
+      "text';drawtext=1",
+      "text[0]",
+      "text,volume=9",
+      "text'quote",
+      'text"quote',
+      "text`cmd`",
+      "text$HOME",
+      "text\\n",
+      "text{a}",
+      "text=x",
+    ]) {
+      expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: hostile }] }), hostile).toThrow(/metacharacter|control characters|must be a string/);
+    }
+    // Newlines are control characters too.
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: "a\nb" }] })).toThrow(/control characters/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: "\u0000" }] })).toThrow(/control characters/);
+  });
+
+  it("bounds overlay text length and rejects empty text", () => {
+    expect(parseProduceRequest({ overlays: [{ kind: "lower_third", text: "x".repeat(MAX_PRODUCE_OVERLAY_TEXT) }] }).overlays?.[0]?.text).toHaveLength(200);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: "x".repeat(201) }] })).toThrow(/at most 200 characters/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: "" }] })).toThrow(/must not be empty/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: "   " }] })).toThrow(/must not be empty/);
+  });
+
+  it("restricts position to finite numbers 0-100 on both axes", () => {
+    expect(parseProduceRequest({ overlays: [{ kind: "clock", position: { x: 0, y: MAX_PRODUCE_POSITION } }] }).overlays?.[0]?.position).toEqual({ x: 0, y: 100 });
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: -1, y: 0 } }] })).toThrow(/position\.x must be between 0 and 100/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: 101, y: 0 } }] })).toThrow(/position\.y|position\.x must be between/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: Number.NaN, y: 0 } }] })).toThrow(/position\.x must be a number/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: "50", y: 0 } }] })).toThrow(/position\.x must be a number/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: 50 } }] })).toThrow(/position\.y/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: 50, y: 0, w: 10 } }] })).toThrow(/position\.w is not allowed/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", position: { x: Number.POSITIVE_INFINITY, y: 0 } }] })).toThrow(/position\.x must be a number|between 0 and 100/);
+  });
+
+  it("keeps overlay kinds closed and per-kind fields exclusive", () => {
+    expect(() => parseProduceRequest({ overlays: [{ kind: "chyron" }] })).toThrow(/overlays\[0\]\.kind must be one of lower_third, logo, clock/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third" }] })).toThrow(/overlays\[0\]\.text must be a string/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo" }] })).toThrow(/overlays\[0\]\.logoStorageKey must be a content-addressed storage key/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", text: "nope" }] })).toThrow(/overlays\[0\]\.text is not allowed/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo", text: "nope" }] })).toThrow(/overlays\[0\]\.text is not allowed/);
+    // A storage key riding on a clock is rejected; the "key"-shaped name trips the
+    // secrets branch first (same precedence as production.ts) — either way, refused.
+    expect(() => parseProduceRequest({ overlays: [{ kind: "clock", logoStorageKey: "sha256/9f2b1c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d.png" }] })).toThrow(/logoStorageKey/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "lower_third", text: "ok", logoStorageKey: "sha256/9f2b1c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d0e0f0a0b0c0d.png" }] })).toThrow(/logoStorageKey/);
+    expect(() => parseProduceRequest({ overlays: [{}] })).toThrow(/overlays\[0\]\.kind must be one of/);
+  });
+
+  it("accepts only content-addressed storage keys for logos (no traversal, no separators)", () => {
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo", logoStorageKey: "../../etc/passwd" }] })).toThrow(/content-addressed storage key/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo", logoStorageKey: "sha256/../x.png" }] })).toThrow(/content-addressed storage key/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo", logoStorageKey: "C:\\evil.png" }] })).toThrow(/content-addressed storage key/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo", logoStorageKey: "file:///tmp/x.png" }] })).toThrow(/content-addressed storage key/);
+    expect(() => parseProduceRequest({ overlays: [{ kind: "logo", logoStorageKey: "png" }] })).toThrow(/content-addressed storage key/);
+  });
+
+  it("validates the voiceover: UUID asset, bounded gain, boolean duck", () => {
+    expect(() => parseProduceRequest({ voiceover: { assetId: "not-a-uuid" } })).toThrow(/voiceover\.assetId must be a UUID/);
+    expect(() => parseProduceRequest({ voiceover: { assetId: voiceoverAssetId, gainDb: -49 } })).toThrow(/gainDb must be a number between -48 and 12 dB/);
+    expect(() => parseProduceRequest({ voiceover: { assetId: voiceoverAssetId, gainDb: 13 } })).toThrow(/gainDb must be a number between/);
+    expect(() => parseProduceRequest({ voiceover: { assetId: voiceoverAssetId, gainDb: "loud" } })).toThrow(/gainDb/);
+    expect(() => parseProduceRequest({ voiceover: { assetId: voiceoverAssetId, duckOriginal: "yes" } })).toThrow(/duckOriginal must be a boolean/);
+    expect(parseProduceRequest({ voiceover: { assetId: voiceoverAssetId } }).voiceover).toEqual({ assetId: voiceoverAssetId });
+  });
+
+  it("bounds outputLabel and the overlay list, and closes the lane enum", () => {
+    expect(() => parseProduceRequest({ outputLabel: "x".repeat(65) })).toThrow(/outputLabel must be 1-64/);
+    expect(() => parseProduceRequest({ outputLabel: "has;semicolon" })).toThrow(/outputLabel must be 1-64/);
+    expect(() => parseProduceRequest({ outputLabel: "=cmd" })).toThrow(/outputLabel must be 1-64/);
+    expect(() => parseProduceRequest({ lane: "cloud" })).toThrow(/lane must be one of local, remote/);
+    expect(() => parseProduceRequest({ overlays: new Array(65).fill({ kind: "clock" }) })).toThrow(/at most 64 entries/);
+    expect(() => parseProduceRequest({ overlays: "clock" })).toThrow(/overlays must be an array/);
+    expect(() => parseProduceRequest("nope")).toThrow(/body must be an object/);
+    expect(() => parseProduceRequest([{ kind: "clock" }])).toThrow(/body must be an object/);
+  });
+
+  it("returns a serializable, JSON-round-trippable request for input_json", () => {
+    const parsed = parseProduceRequest({ overlays: [{ kind: "lower_third", text: "ok", position: { x: 1, y: 2 } }], voiceover: { assetId: voiceoverAssetId, gainDb: 0 } });
+    expect(JSON.parse(JSON.stringify(parsed))).toEqual({
+      overlays: [{ kind: "lower_third", text: "ok", position: { x: 1, y: 2 } }],
+      voiceover: { assetId: voiceoverAssetId, gainDb: 0 },
+    });
+  });
+});
diff --git a/apps/api/src/video/produce-request.ts b/apps/api/src/video/produce-request.ts
new file mode 100644
index 0000000..9019065
--- /dev/null
+++ b/apps/api/src/video/produce-request.ts
@@ -0,0 +1,178 @@
+import { BadRequestException } from "@nestjs/common";
+import { MAX_OVERLAYS } from "../media-control/production.js";
+import { isUuid } from "../http/validation.js";
+
+/**
+ * Producer job intake: the request shape for POST /video/:id/produce.
+ *
+ * Everything accepted here is persisted verbatim into
+ * video_processing_jobs.input_json and later reaches an ffmpeg filtergraph in
+ * the media-worker compositor, so the rules follow
+ * media-control/production.ts: closed enums, exhaustive key allowlists (an
+ * unknown key is rejected, never ignored — that is what keeps a stray
+ * `movie=`/`enable=` field from riding into a filtergraph), bounded geometry,
+ * bounded text, and no filtergraph or shell metacharacter inside operator text.
+ *
+ * The parse is total: it either returns a canonicalized request (fixed key
+ * order, so the stored input_json bytes are deterministic) or throws
+ * BadRequestException with a field path.
+ */
+
+export type ProduceOverlayKind = "lower_third" | "logo" | "clock";
+export type ProduceLane = "local" | "remote";
+
+export const PRODUCE_OVERLAY_KINDS: readonly ProduceOverlayKind[] = ["lower_third", "logo", "clock"];
+export const PRODUCE_LANES: readonly ProduceLane[] = ["local", "remote"];
+
+export const MAX_PRODUCE_OVERLAY_TEXT = 200;
+export const MAX_PRODUCE_LABEL = 64;
+export const PRODUCE_POSITION_MIN = 0;
+export const MAX_PRODUCE_POSITION = 100;
+export const PRODUCE_GAIN_DB_MIN = -48;
+export const PRODUCE_GAIN_DB_MAX = 12;
+
+export interface ProduceOverlay {
+  kind: ProduceOverlayKind;
+  /** lower_third only: the burned-in caption. */
+  text?: string;
+  /** Percent of the output frame, 0-100 on each axis. */
+  position?: { x: number; y: number };
+  /** logo only: storage key of the rendered PNG. */
+  logoStorageKey?: string;
+}
+
+export interface ProduceVoiceover {
+  assetId: string;
+  gainDb?: number;
+  duckOriginal?: boolean;
+}
+
+export interface ProduceRequest {
+  overlays?: ProduceOverlay[];
+  voiceover?: ProduceVoiceover;
+  outputLabel?: string;
+  lane?: ProduceLane;
+}
+
+/** Keys nobody may post, mirroring production.ts: secrets are never accepted. */
+const SECRETISH = /key|secret|token|password|passwd|credential(?!HandleId)|auth/i;
+/**
+ * Characters that change an ffmpeg filtergraph (`;` splits, `[`/`]` label pads,
+ * `,` separates args, `'` quotes, `=` sets an option) or a shell string. A lower
+ * third is operator prose, so the check is a blocklist of these rather than
+ * production.ts's tight label allowlist — prose keeps its punctuation and no
+ * metacharacter survives.
+ */
+const TEXT_FORBIDDEN = new Set([';', "[", "]", "'", '"', "`", "$", "\\", "{", "}", "=", ","]);
+/** Storage keys are content-addressed, flat and extension-suffixed; no traversal, no separators. */
+const STORAGE_KEY = /^[a-z0-9][a-z0-9/._-]{7,255}$/;
+const LABEL = /^[\p{L}\p{N}][\p{L}\p{N} _.-]{0,63}$/u;
+
+function fail(message: string): never {
+  throw new BadRequestException(message);
+}
+
+function record(value: unknown, field: string, allowed: readonly string[]): Record<string, unknown> {
+  if (typeof value !== "object" || value === null || Array.isArray(value)) fail(`${field} must be an object`);
+  for (const key of Object.keys(value)) {
+    if (allowed.includes(key)) continue;
+    if (SECRETISH.test(key)) fail(`${field}.${key}: secrets are never accepted; reference a vault credentialHandleId`);
+    fail(`${field}.${key} is not allowed`);
+  }
+  return value as Record<string, unknown>;
+}
+
+function optional<T>(value: unknown, field: string, parse: (v: unknown, f: string) => T): T | undefined {
+  return value === undefined || value === null ? undefined : parse(value, field);
+}
+
+function text(value: unknown, field: string): string {
+  if (typeof value !== "string") fail(`${field} must be a string`);
+  if (value.trim() === "") fail(`${field} must not be empty`);
+  if (value.length > MAX_PRODUCE_OVERLAY_TEXT) fail(`${field} must be at most ${MAX_PRODUCE_OVERLAY_TEXT} characters`);
+  for (const character of value) {
+    const code = character.codePointAt(0) ?? 0;
+    if (code < 0x20 || code === 0x7f) fail(`${field} must not contain control characters`);
+    if (TEXT_FORBIDDEN.has(character)) fail(`${field} must not contain the filtergraph metacharacter ${JSON.stringify(character)}`);
+  }
+  return value;
+}
+
+function position(value: unknown, field: string): { x: number; y: number } {
+  const p = record(value, field, ["x", "y"]);
+  return { x: coordinate(p.x, `${field}.x`), y: coordinate(p.y, `${field}.y`) };
+}
+
+function coordinate(value: unknown, field: string): number {
+  if (typeof value !== "number" || !Number.isFinite(value)) fail(`${field} must be a number`);
+  if (value < PRODUCE_POSITION_MIN || value > MAX_PRODUCE_POSITION) {
+    fail(`${field} must be between ${PRODUCE_POSITION_MIN} and ${MAX_PRODUCE_POSITION} (percent of frame)`);
+  }
+  return value;
+}
+
+function storageKey(value: unknown, field: string): string {
+  if (typeof value !== "string" || !STORAGE_KEY.test(value) || value.includes("..")) {
+    fail(`${field} must be a content-addressed storage key`);
+  }
+  return value;
+}
+
+function overlay(value: unknown, field: string): ProduceOverlay {
+  if (typeof value !== "object" || value === null || Array.isArray(value)) fail(`${field} must be an object`);
+  const kind = (value as Record<string, unknown>).kind;
+  if (kind !== "lower_third" && kind !== "logo" && kind !== "clock") {
+    fail(`${field}.kind must be one of ${PRODUCE_OVERLAY_KINDS.join(", ")}`);
+  }
+  // Per-kind allowlist: a clock has no text and no asset, a logo has no caption.
+  const allowed = kind === "lower_third" ? ["kind", "text", "position"] : kind === "logo" ? ["kind", "logoStorageKey", "position"] : ["kind", "position"];
+  const o = record(value, field, allowed);
+  return {
+    kind,
+    ...(kind === "lower_third"
+      ? { text: text(o.text, `${field}.text`) }
+      : kind === "logo"
+        ? { logoStorageKey: storageKey(o.logoStorageKey, `${field}.logoStorageKey`) }
+        : {}),
+    ...(o.position === undefined ? {} : { position: position(o.position, `${field}.position`) }),
+  };
+}
+
+function voiceover(value: unknown, field: string): ProduceVoiceover {
+  const v = record(value, field, ["assetId", "gainDb", "duckOriginal"]);
+  if (typeof v.assetId !== "string" || !isUuid(v.assetId)) fail(`${field}.assetId must be a UUID`);
+  const gainDb = optional(v.gainDb, `${field}.gainDb`, (g, f) => {
+    if (typeof g !== "number" || !Number.isFinite(g) || g < PRODUCE_GAIN_DB_MIN || g > PRODUCE_GAIN_DB_MAX) {
+      fail(`${f} must be a number between ${PRODUCE_GAIN_DB_MIN} and ${PRODUCE_GAIN_DB_MAX} dB`);
+    }
+    return g;
+  });
+  const duckOriginal = optional(v.duckOriginal, `${field}.duckOriginal`, (d, f) => {
+    if (typeof d !== "boolean") fail(`${f} must be a boolean`);
+    return d;
+  });
+  return { assetId: v.assetId, ...(gainDb === undefined ? {} : { gainDb }), ...(duckOriginal === undefined ? {} : { duckOriginal }) };
+}
+
+/** Parse and canonicalize a produce request; throws BadRequestException on the first problem. */
+export function parseProduceRequest(value: unknown, field = "body"): ProduceRequest {
+  const b = record(value, field, ["overlays", "voiceover", "outputLabel", "lane"]);
+  if (b.overlays !== undefined && b.overlays !== null) {
+    if (!Array.isArray(b.overlays)) fail(`${field}.overlays must be an array`);
+    if (b.overlays.length > MAX_OVERLAYS) fail(`${field}.overlays allows at most ${MAX_OVERLAYS} entries`);
+  }
+  if (b.lane !== undefined && b.lane !== null && b.lane !== "local" && b.lane !== "remote") {
+    fail(`${field}.lane must be one of ${PRODUCE_LANES.join(", ")}`);
+  }
+  const outputLabel = optional(b.outputLabel, `${field}.outputLabel`, (l, f) => {
+    if (typeof l !== "string" || !LABEL.test(l)) fail(`${f} must be 1-${MAX_PRODUCE_LABEL} letters, digits, spaces, '_', '.', '-'`);
+    return l;
+  });
+  const overlays = (b.overlays ?? []).map((item, index) => overlay(item, `${field}.overlays[${index}]`));
+  return {
+    ...(overlays.length === 0 ? {} : { overlays }),
+    ...(b.voiceover === undefined || b.voiceover === null ? {} : { voiceover: voiceover(b.voiceover, `${field}.voiceover`) }),
+    ...(outputLabel === undefined ? {} : { outputLabel }),
+    ...(b.lane === undefined || b.lane === null ? {} : { lane: b.lane }),
+  };
+}
diff --git a/apps/api/src/video/test-fixtures.ts b/apps/api/src/video/test-fixtures.ts
index 63bdc2a..8e61d08 100644
--- a/apps/api/src/video/test-fixtures.ts
+++ b/apps/api/src/video/test-fixtures.ts
@@ -14,6 +14,8 @@ export interface FakeVideoDatabase {
   asset?: Record<string, unknown>;
   job?: Record<string, unknown>;
   transitions?: string[];
+  /** Raw INSERT statements seen, for asserting what intake wrote. */
+  statements?: Array<{ sql: string; values: readonly unknown[] }>;
 }
 
 function result(rows: Array<Record<string, unknown>>): QueryResult<Record<string, unknown>> {
@@ -24,7 +26,7 @@ export function serviceWithDatabase(
   database: FakeVideoDatabase,
   probe: VideoServiceDependencies["probe"],
   storageOverride?: StorageService,
-): { service: VideoService; appendAudit: VideoServiceDependencies["appendAudit"]; storage: StorageService; objects: Map<string, Buffer> } {
+): { service: VideoService; appendAudit: VideoServiceDependencies["appendAudit"] & { mockClear(): void }; storage: StorageService; objects: Map<string, Buffer> } {
   const objects = new Map<string, Buffer>();
   const storage: StorageService = storageOverride ?? {
     putContent: vi.fn(async (bytes: Buffer, contentType: string) => {
@@ -43,6 +45,7 @@ export function serviceWithDatabase(
     presign: async () => { throw new Error("Encrypted source must be decrypted before probing"); },
   };
   database.transitions = [];
+  database.statements = [];
   const client = {
     async query(sql: string, values: readonly unknown[] = []): Promise<QueryResult<Record<string, unknown>>> {
       if (sql.includes("INSERT INTO video_assets")) {
@@ -64,11 +67,17 @@ export function serviceWithDatabase(
         return result([database.asset]);
       }
       if (sql.includes("INSERT INTO video_processing_jobs")) {
+        database.statements?.push({ sql, values });
+        const produce = sql.includes("input_json");
         database.job = {
           id: jobId,
           workspace_id: values[0],
           video_asset_id: values[1],
           state: "queued",
+          // kind/input_json exist only since migration 039; produce rows carry them.
+          // pg returns jsonb already parsed, not as the JSON text we sent.
+          ...(produce ? { kind: values[2], input_json: JSON.parse(String(values[3])) } : {}),
+          produced_asset_id: null,
           progress_percent: 0,
           output_key: null,
           error: null,
diff --git a/apps/api/src/video/video.controller.ts b/apps/api/src/video/video.controller.ts
index f4612b6..5fd8233 100644
--- a/apps/api/src/video/video.controller.ts
+++ b/apps/api/src/video/video.controller.ts
@@ -19,10 +19,12 @@ import { parseId, parseLimit, requireObject, requireSession, requireString } fro
 import { RbacGuard, RequirePermission, type AuthenticatedRequest } from "../rbac/rbac.guard.js";
 import {
   VideoService,
+  type ProduceRequestResult,
   type VideoLibraryPage,
   type VideoStatus,
   type VideoUploadResult,
 } from "./video.service.js";
+import { parseProduceRequest } from "./produce-request.js";
 import { MAX_VIDEO_UPLOAD_BYTES } from "./upload-limits.js";
 import { loadDriveBytes, loadMatrixBytes, parseMxcUri } from "./import-sources.js";
 
@@ -91,6 +93,20 @@ export class VideoController {
     return this.video.listVideos(requireSession(request).workspaceId, cursor, parseLimit(limit, 50, 200));
   }
 
+  @Post(":id/produce")
+  @RequirePermission("media.manage")
+  async produce(
+    @Req() request: Request & AuthenticatedRequest,
+    @Param("id") id: string,
+    @Body() body: unknown,
+  ): Promise<ProduceRequestResult> {
+    const session = requireSession(request);
+    // Strict allowlist parse: unknown keys are rejected, never ignored, so no
+    // field can ride into input_json (and on into a worker filtergraph).
+    const produce = parseProduceRequest(body);
+    return this.video.produceVideo(parseId(id), session.workspaceId, produce, session.userId);
+  }
+
   @Get(":id/status")
   @RequirePermission("media.view")
   async status(
diff --git a/apps/api/src/video/video.service.test.ts b/apps/api/src/video/video.service.test.ts
index c76c637..e08c310 100644
--- a/apps/api/src/video/video.service.test.ts
+++ b/apps/api/src/video/video.service.test.ts
@@ -3,6 +3,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import { VideoService } from "./video.service.js";
 import { assetId, serviceWithDatabase, workspaceId, type FakeVideoDatabase } from "./test-fixtures.js";
 import { MAX_VIDEO_UPLOAD_BYTES } from "./upload-limits.js";
+import type { ProduceRequest } from "./produce-request.js";
 
 afterEach(() => vi.unstubAllEnvs());
 
@@ -26,6 +27,7 @@ describe("video byte ingest and processing-job state machine", () => {
     expect(uploaded.videoAsset).toMatchObject({ sizeBytes: bytes.length, width: 1280, height: 720, durationMs: 42_000, codec: "h264" });
     expect(uploaded.processingJob).toMatchObject({ state: "complete", progressPercent: 100, outputKey: uploaded.videoAsset.storageKey });
     expect(uploaded.processingJob.processingNote).toContain("Transcode skipped");
+    // ...and the produce INSERT is the only thing that followed it.
     expect(database.transitions).toEqual(["queued", "probing", "transcoding", "complete"]);
     await expect(stat(inputPath)).rejects.toMatchObject({ code: "ENOENT" });
     expect(appendAudit).toHaveBeenCalledWith(workspaceId, expect.objectContaining({ action: "video.uploaded", targetId: assetId }));
@@ -98,6 +100,59 @@ describe("video byte ingest and processing-job state machine", () => {
     expect(objects.get(uploaded.videoAsset.storageKey)).toEqual(bytes);
   });
 
+  it("queues a compose job with the canonicalized request in input_json and audits it", async () => {
+    const database: FakeVideoDatabase = {};
+    const { service, appendAudit } = serviceWithDatabase(database, async () => ({}));
+    await service.uploadVideoBytes(workspaceId, Buffer.from("source"), "video/mp4");
+    appendAudit.mockClear();
+    const request: ProduceRequest = {
+      overlays: [{ kind: "lower_third", text: "Live now", position: { x: 0, y: 100 } }],
+      outputLabel: "Recap",
+    };
+    const produced = await service.produceVideo(assetId, workspaceId, request, "10000000-0000-4000-8000-000000000009");
+    // kind is compose unless a voiceover is present, then mix.
+    expect(produced.job).toMatchObject({ state: "queued", kind: "compose", videoAssetId: assetId });
+    // Nothing produced yet: the job points at no output asset until the worker finishes.
+    expect("producedAssetId" in produced.job).toBe(false);
+    expect(produced.videoAsset.id).toBe(assetId);
+    expect(database.statements?.at(-1)).toMatchObject({
+      sql: expect.stringContaining("INSERT INTO video_processing_jobs (workspace_id, video_asset_id, state, kind, input_json)"),
+      values: [workspaceId, assetId, "compose", JSON.stringify({ ...request, requestedBy: "10000000-0000-4000-8000-000000000009" })],
+    });
+    // input_json is passed as jsonb text and never leaves the tenant transaction.
+    expect(JSON.parse(String(database.statements?.at(-1)?.values[3]))).toEqual({ overlays: [{ kind: "lower_third", text: "Live now", position: { x: 0, y: 100 } }], outputLabel: "Recap", requestedBy: "10000000-0000-4000-8000-000000000009" });
+    expect(appendAudit).toHaveBeenCalledWith(workspaceId, expect.objectContaining({
+      action: "video.produce_requested",
+      targetId: assetId,
+      diff: expect.objectContaining({ kind: "compose", overlayCount: 1, voiceover: null, outputLabel: "Recap" }),
+    }));
+    // The produce row never disturbs the probe state machine of the source:
+    // the fake holds one job slot, so the probe transitions are all still there.
+    // ...and the produce INSERT is the only thing that followed it.
+    expect(database.transitions).toEqual(["queued", "probing", "transcoding", "complete", "queued"]);
+  });
+
+  it("queues a mix job when a voiceover is present and does not touch the source asset", async () => {
+    const database: FakeVideoDatabase = {};
+    const { service } = serviceWithDatabase(database, async () => ({}));
+    await service.uploadVideoBytes(workspaceId, Buffer.from("source"), "video/mp4");
+    await service.produceVideo(assetId, workspaceId, {
+      voiceover: { assetId: "20000000-0000-4000-8000-000000000004", gainDb: -6, duckOriginal: true },
+      lane: "remote",
+    }, "10000000-0000-4000-8000-000000000009");
+    expect(database.statements?.at(-1)?.values[2]).toBe("mix");
+    expect(JSON.parse(String(database.statements?.at(-1)?.values[3]))).toEqual({
+      voiceover: { assetId: "20000000-0000-4000-8000-000000000004", gainDb: -6, duckOriginal: true },
+      lane: "remote",
+      requestedBy: "10000000-0000-4000-8000-000000000009",
+    });
+  });
+
+  it("refuses to produce from an unknown asset", async () => {
+    const { service } = serviceWithDatabase({}, async () => ({}));
+    await expect(service.produceVideo("30000000-0000-4000-8000-000000000005", workspaceId, {}, "u")).rejects.toMatchObject({ status: 404 });
+  });
+
   it("rejects empty or non-video uploads before storage", async () => {
     const { service, storage } = serviceWithDatabase({}, async () => ({}));
     await expect(service.uploadVideoBytes(workspaceId, Buffer.alloc(0), "video/mp4")).rejects.toMatchObject({ status: 400 });
diff --git a/apps/api/src/video/video.service.ts b/apps/api/src/video/video.service.ts
index 4147579..72cfd68 100644
--- a/apps/api/src/video/video.service.ts
+++ b/apps/api/src/video/video.service.ts
@@ -7,6 +7,7 @@ import { appendTenantAudit, type AuditEvent } from "../audit/audit.service.js";
 import { withTenant } from "../db/client.js";
 import { probeVideoFile, type VideoProbeResult } from "./ffprobe.js";
 import { S3Storage, s3ConfigFromEnv, type StorageService } from "../storage/storage.js";
+import { type ProduceRequest } from "./produce-request.js";
 import { MAX_VIDEO_UPLOAD_BYTES } from "./upload-limits.js";
 
 const NO_OP_TRANSCODE_NOTE = "Transcode skipped: original stored object retained; rendering belongs to the media-worker compositor.";
@@ -28,17 +29,35 @@ export interface VideoAssetRecord {
   thumbnailKey?: string;
 }
 
+export type VideoProcessingJobKind = "probe" | "compose" | "mix";
+
 export interface VideoProcessingJobRecord {
   id: string;
   workspaceId: string;
   videoAssetId: string;
   state: VideoProcessingJobState;
+  /** What the media-worker should do; 'probe' is the ingest default. */
+  kind: VideoProcessingJobKind;
+  /** Producer request (kind compose/mix): { ...request, requestedBy }. */
+  input?: ProduceJobInput;
+  /** The video_assets row this job writes when it finishes. */
+  producedAssetId?: string;
   progressPercent?: number;
   outputKey?: string;
   error?: string;
   processingNote?: string;
 }
 
+export interface ProduceJobInput extends ProduceRequest {
+  requestedBy: string;
+}
+
+export interface ProduceRequestResult {
+  /** The newly queued compose/mix job. */
+  job: VideoProcessingJobRecord;
+  videoAsset: VideoAssetRecord;
+}
+
 export interface VideoPublicationSummary {
   connectionId: string;
   remoteId: string;
@@ -176,7 +195,8 @@ export class VideoService {
         `SELECT va.*,
                 j.id AS job_id, j.video_asset_id AS job_video_asset_id,
                 j.state AS job_state, j.progress_percent AS job_progress_percent,
-                j.output_key AS job_output_key, j.error AS job_error
+                j.output_key AS job_output_key, j.error AS job_error,
+                j.kind AS job_kind, j.input_json AS job_input_json, j.produced_asset_id AS job_produced_asset_id
          FROM video_assets va
          LEFT JOIN LATERAL (
            SELECT * FROM video_processing_jobs
@@ -345,6 +365,43 @@ export class VideoService {
     });
   }
 
+  /**
+   * Queue a derived asset: burn overlays (and optionally mix a voiceover) over an
+   * existing asset. Validates nothing itself — the controller parses the request
+   * with parseProduceRequest before calling, and the media-worker re-validates.
+   */
+  async produceVideo(
+    assetId: string,
+    workspaceId: string,
+    request: ProduceRequest,
+    requestedBy: string,
+  ): Promise<ProduceRequestResult> {
+    const input: ProduceJobInput = { ...request, requestedBy };
+    const kind: VideoProcessingJobKind = request.voiceover === undefined ? "compose" : "mix";
+    const created = await this.dependencies.tenantTransaction(workspaceId, async (client) => {
+      const source = await client.query("SELECT * FROM video_assets WHERE id = $1", [assetId]);
+      if (source.rowCount !== 1) throw new NotFoundException(`video ${assetId} not found`);
+      const jobResult = await client.query(
+        `INSERT INTO video_processing_jobs (workspace_id, video_asset_id, state, kind, input_json)
+         VALUES ($1, $2, 'queued', $3, $4::jsonb) RETURNING *`,
+        [workspaceId, assetId, kind, JSON.stringify(input)],
+      );
+      return {
+        videoAsset: assetFromRow(requiredRow(source.rows[0], "source video asset")),
+        job: jobFromRow(requiredRow(jobResult.rows[0], "created produce job")),
+      };
+    });
+    await this.audit(workspaceId, "video.produce_requested", assetId, {
+      kind,
+      jobId: created.job.id,
+      overlayCount: request.overlays?.length ?? 0,
+      voiceover: request.voiceover === undefined ? null : { assetId: request.voiceover.assetId, duckOriginal: request.voiceover.duckOriginal ?? false },
+      outputLabel: request.outputLabel ?? null,
+      lane: request.lane ?? null,
+    });
+    return created;
+  }
+
   async deleteVideo(assetId: string, workspaceId: string): Promise<void> {
     // Objects are shared by content hash across assets/workspaces. Retain for future
     // reference-aware GC; deleting here could destroy another asset's source.
@@ -373,7 +430,7 @@ export class VideoService {
 
   private async audit(
     workspaceId: string,
-    action: "video.uploaded" | "video.probed" | "video.deleted" | "video.imported",
+    action: "video.uploaded" | "video.probed" | "video.deleted" | "video.imported" | "video.produce_requested",
     targetId: string,
     diff: Record<string, unknown>,
   ): Promise<void> {
@@ -420,6 +477,7 @@ function assetFromRow(row: Record<string, unknown>): VideoAssetRecord {
     ...optionalString("codec", row.codec),
     ...optionalString("audioCodec", row.audio_codec),
     ...optionalString("thumbnailKey", row.thumbnail_key),
+    ...optionalString("derivedFrom", row.derived_from),
   };
 }
 
@@ -429,6 +487,9 @@ function jobFromRow(row: Record<string, unknown>): VideoProcessingJobRecord {
     workspaceId: String(row.workspace_id),
     videoAssetId: String(row.video_asset_id),
     state: processingState(row.state),
+    kind: processingKind(row.kind),
+    ...(row.input_json === null || row.input_json === undefined ? {} : { input: requiredRow(row.input_json, "job input") as unknown as ProduceJobInput }),
+    ...optionalString("producedAssetId", row.produced_asset_id),
     ...optionalNumber("progressPercent", row.progress_percent),
     ...optionalString("outputKey", row.output_key),
     ...optionalString("error", row.error),
@@ -444,6 +505,9 @@ function joinedJobFromRow(row: Record<string, unknown>): VideoProcessingJobRecor
     progress_percent: row.job_progress_percent,
     output_key: row.job_output_key,
     error: row.job_error,
+    kind: row.job_kind,
+    input_json: row.job_input_json,
+    produced_asset_id: row.job_produced_asset_id,
   });
   return {
     ...job,
@@ -469,6 +533,13 @@ function publicationFromJson(row: Record<string, unknown>): VideoPublicationSumm
   };
 }
 
+function processingKind(value: unknown): VideoProcessingJobKind {
+  if (value === "probe" || value === "compose" || value === "mix") return value;
+  // Rows created before migration 039 have no kind and are probe jobs.
+  if (value === null || value === undefined) return "probe";
+  throw new Error(`invalid video processing job kind: ${String(value)}`);
+}
+
 function processingState(value: unknown): VideoProcessingJobState {
   if (
     value === "queued" ||