Implement ADTS muxer :3

dev/convert.html

@@ -24,7 +24,9 @@
 			chunked: true,
 			chunkSize: 2**20
 		});
-		const outputFormat = new Mediabunny.Mp3OutputFormat({});
+		const outputFormat = new Mediabunny.AdtsOutputFormat({
+			onFrame: console.log
+		});
 
 		const button = document.createElement('button');
 		button.textContent = 'Cancel';

docs/guide/introduction.md

@@ -12,7 +12,7 @@ Here's a long list of stuff this library does:
 - Converting media files
 - Hardware-accelerated decoding & encoding (via the WebCodecs API)
 - Support for multiple video, audio and subtitle tracks
-- Read & write support for many container formats (.mp4, .mov, .webm, .mkv, .mp3, .wav, .ogg), including variations such as MP4 with Fast Start, fragmented MP4, or streamable Matroska
+- Read & write support for many container formats (.mp4, .mov, .webm, .mkv, .mp3, .wav, .ogg, .aac), including variations such as MP4 with Fast Start, fragmented MP4, or streamable Matroska
 - Support for 25 different codecs
 - Lazy, optimized, on-demand file reading
 - Input and output streaming, arbitrary file size support

docs/guide/output-formats.md

@@ -245,3 +245,24 @@ type WavOutputFormatOptions = {
 	When enabled, an RF64 file be written, allowing for file sizes to exceed 4 GiB, which is otherwise not possible for regular WAVE files.
 - `onHeader`\
 	Will be called once the file header is written. The header consists of the RIFF header, the format chunk, and the start of the data chunk (with a placeholder size of 0).
+
+## ADTS
+
+This output format creates ADTS (.aac) files.
+```ts
+import { Output, AdtsOutputFormat } from 'mediabunny';	
+
+const output = new Output({
+	format: new AdtsOutputFormat(options),
+	// ...
+});
+```
+
+The following options are available:
+```ts
+type AdtsOutputFormatOptions = {
+	onFrame?: (data: Uint8Array, position: number) => unknown;
+};
+```
+- `onFrame`\
+	Will be called for each ADTS frame that is written.

docs/guide/supported-formats-and-codecs.md

@@ -11,6 +11,7 @@ Mediabunny supports many commonly used media container formats, all of which are
 - Ogg (.ogg)
 - MP3 (.mp3)
 - WAVE (.wav)
+- ADTS (.aac)
 
 ## Codecs
 
@@ -60,33 +61,33 @@ Mediabunny ships with built-in decoders and encoders for all audio PCM codecs, m
 
 Not all codecs can be used with all containers. The following table specifies the supported codec-container combinations:
 
-|                | .mp4 | .mov  | .mkv  | .webm[^1] | .ogg  | .mp3  | .wav  |
-|:--------------:|:--------:|:-----:|:-----:|:---------:|:-----:|:-----:|:-----:|
-| `'avc'`        |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'hevc'`       |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'vp8'`        |    ✓     |   ✓   |   ✓   |     ✓     |       |       |       |
-| `'vp9'`        |    ✓     |   ✓   |   ✓   |     ✓     |       |       |       |
-| `'av1'`        |    ✓     |   ✓   |   ✓   |     ✓     |       |       |       |
-| `'aac'`        |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'opus'`       |    ✓     |   ✓   |   ✓   |     ✓     |   ✓   |       |       |
-| `'mp3'`        |    ✓     |   ✓   |   ✓   |           |       |   ✓   |       |
-| `'vorbis'`     |    ✓     |   ✓   |   ✓   |     ✓     |   ✓   |       |       |
-| `'flac'`       |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'pcm-u8'`     |          |   ✓   |   ✓   |           |       |       |   ✓   |
-| `'pcm-s8'`     |          |   ✓   |       |           |       |       |       |
-| `'pcm-s16'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |
-| `'pcm-s16be'`  |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'pcm-s24'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |
-| `'pcm-s24be'`  |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'pcm-s32'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |
-| `'pcm-s32be'`  |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'pcm-f32'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |
-| `'pcm-f32be'`  |    ✓     |   ✓   |       |           |       |       |       |
-| `'pcm-f64'`    |    ✓     |   ✓   |   ✓   |           |       |       |       |
-| `'pcm-f64be'`  |    ✓     |   ✓   |       |           |       |       |       |
-| `'ulaw'`       |          |   ✓   |       |           |       |       |   ✓   |
-| `'alaw'`       |          |   ✓   |       |           |       |       |   ✓   |
-| `'webvtt'`[^2] |   (✓)    |       |  (✓)  |    (✓)    |       |       |       |
+|                |   .mp4   | .mov  | .mkv  | .webm[^1] | .ogg  | .mp3  | .wav  | .aac  |
+|:--------------:|:--------:|:-----:|:-----:|:---------:|:-----:|:-----:|:-----:|:-----:|
+| `'avc'`        |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'hevc'`       |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'vp8'`        |    ✓     |   ✓   |   ✓   |     ✓     |       |       |       |       |
+| `'vp9'`        |    ✓     |   ✓   |   ✓   |     ✓     |       |       |       |       |
+| `'av1'`        |    ✓     |   ✓   |   ✓   |     ✓     |       |       |       |       |
+| `'aac'`        |    ✓     |   ✓   |   ✓   |           |       |       |       |   ✓   |
+| `'opus'`       |    ✓     |   ✓   |   ✓   |     ✓     |   ✓   |       |       |       |
+| `'mp3'`        |    ✓     |   ✓   |   ✓   |           |       |   ✓   |       |       |
+| `'vorbis'`     |    ✓     |   ✓   |   ✓   |     ✓     |   ✓   |       |       |       |
+| `'flac'`       |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'pcm-u8'`     |          |   ✓   |   ✓   |           |       |       |   ✓   |       |
+| `'pcm-s8'`     |          |   ✓   |       |           |       |       |       |       |
+| `'pcm-s16'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |       |
+| `'pcm-s16be'`  |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'pcm-s24'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |       |
+| `'pcm-s24be'`  |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'pcm-s32'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |       |
+| `'pcm-s32be'`  |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'pcm-f32'`    |    ✓     |   ✓   |   ✓   |           |       |       |   ✓   |       |
+| `'pcm-f32be'`  |    ✓     |   ✓   |       |           |       |       |       |       | 
+| `'pcm-f64'`    |    ✓     |   ✓   |   ✓   |           |       |       |       |       |
+| `'pcm-f64be'`  |    ✓     |   ✓   |       |           |       |       |       |       |
+| `'ulaw'`       |          |   ✓   |       |           |       |       |   ✓   |       |
+| `'alaw'`       |          |   ✓   |       |           |       |       |   ✓   |       |
+| `'webvtt'`[^2] |   (✓)    |       |  (✓)  |    (✓)    |       |       |       |       |
 
 
 [^1]: WebM only supports a small subset of the codecs supported by Matroska. However, this library can technically read all codecs from a WebM that are supported by Matroska.

src/adts/adts-muxer.ts

@@ -0,0 +1,125 @@
+/*!
+ * Copyright (c) 2025-present, Vanilagy and contributors
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+import { AacAudioSpecificConfig, parseAacAudioSpecificConfig, validateAudioChunkMetadata } from '../codec';
+import { assert, toUint8Array } from '../misc';
+import { Muxer } from '../muxer';
+import { Output, OutputAudioTrack } from '../output';
+import { AdtsOutputFormat } from '../output-format';
+import { EncodedPacket } from '../packet';
+import { Writer } from '../writer';
+
+export class AdtsMuxer extends Muxer {
+	private format: AdtsOutputFormat;
+	private writer: Writer;
+	private header = new Uint8Array(7);
+	private audioSpecificConfig: AacAudioSpecificConfig | null = null;
+
+	constructor(output: Output, format: AdtsOutputFormat) {
+		super(output);
+
+		this.format = format;
+		this.writer = output._writer;
+	}
+
+	async start() {
+		// Nothing needed here
+	}
+
+	async getMimeType() {
+		return 'audio/aac';
+	}
+
+	async addEncodedVideoPacket() {
+		throw new Error('ADTS does not support video.');
+	}
+
+	async addEncodedAudioPacket(
+		track: OutputAudioTrack,
+		packet: EncodedPacket,
+		meta?: EncodedAudioChunkMetadata,
+	) {
+		// https://wiki.multimedia.cx/index.php/ADTS (last visited: 2025/08/17)
+
+		const release = await this.mutex.acquire();
+
+		try {
+			if (!this.audioSpecificConfig) {
+				validateAudioChunkMetadata(meta);
+
+				const description = meta?.decoderConfig?.description;
+				assert(description);
+
+				this.audioSpecificConfig = parseAacAudioSpecificConfig(toUint8Array(description));
+			}
+
+			const syncword = 0b1111_11111111;
+			this.header[0] = (syncword >> 4);
+
+			const mpegVersion = 0;
+			const layer = 0;
+			const protectionAbsence = 1;
+			this.header[1] = (syncword << 4)
+				| (mpegVersion << 3)
+				| (layer << 1)
+				| protectionAbsence;
+
+			const privateBit = 0;
+			this.header[2] = (((this.audioSpecificConfig.objectType - 1) & 0b11) << 6)
+				| ((this.audioSpecificConfig.frequencyIndex & 0b1111) << 2)
+				| (privateBit << 1)
+				| ((this.audioSpecificConfig.channelConfiguration & 0b111) >> 2);
+
+			const originality = 0;
+			const homeUsage = 0;
+			const copyrightIdBit = 0;
+			const copyrightIdStart = 0;
+			const frameLength = (packet.data.byteLength + this.header.byteLength) & 0b11111_11111111;
+			this.header[3] = ((this.audioSpecificConfig.channelConfiguration & 0b111) << 6)
+				| (originality << 5)
+				| (homeUsage << 4)
+				| (copyrightIdBit << 3)
+				| (copyrightIdStart << 2)
+				| (frameLength >> 11);
+
+			this.header[4] = (frameLength >> 3);
+
+			const bufferFullness = 0x7ff; // Variable bitrate
+			this.header[5] = (frameLength << 5)
+				| (bufferFullness >> 6);
+
+			const numberOfAacFrames = 1;
+			this.header[6] = (bufferFullness << 2)
+				| (numberOfAacFrames - 1);
+
+			// Omit CRC check
+
+			const startPos = this.writer.getPos();
+			this.writer.write(this.header);
+			this.writer.write(packet.data);
+
+			if (this.format._options.onFrame) {
+				const frameBytes = new Uint8Array(frameLength);
+				frameBytes.set(this.header, 0);
+				frameBytes.set(packet.data, this.header.byteLength);
+
+				this.format._options.onFrame(frameBytes, startPos);
+			}
+
+			await this.writer.flush();
+		} finally {
+			release();
+		}
+	}
+
+	async addSubtitleCue() {
+		throw new Error('ADTS does not support subtitles.');
+	}
+
+	async finalize() {}
+}

src/codec.ts

@@ -561,7 +561,15 @@ export const extractAudioCodecString = (trackInfo: {
 	throw new TypeError(`Unhandled codec '${codec}'.`);
 };
 
-export const parseAacAudioSpecificConfig = (bytes: Uint8Array | null) => {
+export type AacAudioSpecificConfig = {
+	objectType: number;
+	frequencyIndex: number;
+	sampleRate: number | null;
+	channelConfiguration: number;
+	numberOfChannels: number | null;
+};
+
+export const parseAacAudioSpecificConfig = (bytes: Uint8Array | null): AacAudioSpecificConfig => {
 	if (!bytes || bytes.byteLength < 2) {
 		throw new TypeError('AAC description must be at least 2 bytes long.');
 	}

src/index.ts

@@ -35,6 +35,8 @@ export {
 	WavOutputFormatOptions,
 	OggOutputFormat,
 	OggOutputFormatOptions,
+	AdtsOutputFormat,
+	AdtsOutputFormatOptions,
 	TrackCountLimits,
 	InclusiveIntegerRange,
 } from './output-format';

src/output-format.ts

@@ -6,6 +6,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
+import { AdtsMuxer } from './adts/adts-muxer';
 import {
 	AUDIO_CODECS,
 	AudioCodec,
@@ -705,3 +706,74 @@ export class OggOutputFormat extends OutputFormat {
 		return false;
 	}
 }
+
+/**
+ * ADTS-specific output options.
+ * @public
+ */
+export type AdtsOutputFormatOptions = {
+	/**
+	 * Will be called for each ADTS frame that is written.
+	 *
+	 * @param data - The raw bytes.
+	 * @param position - The byte offset of the data in the file.
+	 */
+	onFrame?: (data: Uint8Array, position: number) => unknown;
+};
+
+/**
+ * ADTS file format.
+ * @public
+ */
+export class AdtsOutputFormat extends OutputFormat {
+	/** @internal */
+	_options: AdtsOutputFormatOptions;
+
+	constructor(options: AdtsOutputFormatOptions = {}) {
+		if (!options || typeof options !== 'object') {
+			throw new TypeError('options must be an object.');
+		}
+		if (options.onFrame !== undefined && typeof options.onFrame !== 'function') {
+			throw new TypeError('options.onFrame, when provided, must be a function.');
+		}
+
+		super();
+
+		this._options = options;
+	}
+
+	/** @internal */
+	_createMuxer(output: Output) {
+		return new AdtsMuxer(output, this);
+	}
+
+	/** @internal */
+	get _name() {
+		return 'ADTS';
+	}
+
+	getSupportedTrackCounts(): TrackCountLimits {
+		return {
+			video: { min: 0, max: 0 },
+			audio: { min: 1, max: 1 },
+			subtitle: { min: 0, max: 0 },
+			total: { min: 1, max: 1 },
+		};
+	}
+
+	get fileExtension() {
+		return '.aac';
+	}
+
+	get mimeType() {
+		return 'audio/aac';
+	}
+
+	getSupportedCodecs(): MediaCodec[] {
+		return ['aac'];
+	}
+
+	get supportsVideoRotationMetadata() {
+		return false;
+	}
+}