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packages/media/audio/audio-codec-ffmpeg-wasm/src/encode/encode-pipeline.md

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+# `encode-pipeline.ts`
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+
+## Purpose
+
+This module owns the pure logic of the encode pipeline: validating the
+requested format against the supported set *before* the worker is touched,
+interleaving per-channel PCM into a single `Float32Array`, projecting
+that into ffmpeg's `f32le` wire format, building the format-specific
+ffmpeg command for each of `wav` / `mp3` / `ogg` / `opus` / `flac` /
+`aac` / `webm`, and dispatching the call through the supplied
+`WorkerHost`. All MEMFS lifecycle is owned by the host.
+
+## Features
+
+- `interleave` and `float32ToBytes` produce the exact wire layout ffmpeg
+  expects for `-f f32le`.
+- `buildCommand` returns the ffmpeg argument list per supported format,
+  honouring caller-supplied `bitrate` (`mp3`, `opus`, `aac`, `webm`) and
+  `quality` (`ogg`).
+- `assertSupported` throws `UNSUPPORTED_CODEC` synchronously, before any
+  worker message is posted — required by the spec.
+- `runEncode` drives the full pipeline through `WorkerHost.submitFfmpeg`.
+
+## Usage: Basic
+
+```ts
+import { runEncode } from "@suaveplan/audio-codec-ffmpeg-wasm/encode/encode-pipeline";
+
+const bytes = await runEncode({
+    host,
+    channelData: [leftFloats, rightFloats],
+    format: "mp3",
+    sampleRate: 44_100,
+    bitrate: 256_000,
+});
+```
+
+## Usage: Advanced
+
+```ts
+import {
+    runEncode,
+    interleave,
+    buildCommand,
+} from "@suaveplan/audio-codec-ffmpeg-wasm/encode/encode-pipeline";
+
+// Inspect the command ffmpeg will be asked to run
+const cmd = buildCommand("opus", 48_000, 1, 96_000);
+console.log(cmd.args);
+
+const interleaved = interleave([mono]);
+const result = await runEncode({
+    host,
+    channelData: [mono],
+    format: "opus",
+    sampleRate: 48_000,
+    bitrate: 96_000,
+    signal: controller.signal,
+    timeoutMs: 60_000,
+});
+```
+
+## API Reference
+
+- `interleave(channelData): Float32Array`.
+- `float32ToBytes(samples): Uint8Array`.
+- `buildCommand(format, sampleRate, channels, bitrate?, quality?): FormatCommand`.
+- `runEncode(opts: EncodePipelineOptions): Promise<Uint8Array>`.
+
+## Implementation Notes
+
+`assertSupported` is intentionally written as a TypeScript `asserts`
+function so its throw branch narrows the format type for the rest of the
+function — no extra runtime branch is needed. Format-specific defaults
+(192 kbps for MP3/AAC, 96 kbps for Opus/WebM, q=5 for Vorbis) are
+chosen to match the ffmpeg.wasm reference build's documented sweet
+spots; callers always override via `bitrate`/`quality` for production
+use. The interleaved `Float32Array` is wrapped in a `Uint8Array` view
+without an extra copy so the worker `postMessage` boundary takes one
+transferable buffer instead of two.