Add @mediabunny/aac-encoder extension package

packages/aac-encoder/src/bridge.c

@@ -0,0 +1,190 @@
+/*!
+ * Copyright (c) 2026-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/.
+ */
+
+#include <emscripten.h>
+#include <stdlib.h>
+#include <string.h>
+#include "libavcodec/avcodec.h"
+#include "libavutil/opt.h"
+#include "libavutil/channel_layout.h"
+#include "libavutil/log.h"
+
+typedef struct {
+	AVCodecContext *codec_ctx;
+	AVPacket *packet;
+	AVFrame *frame;
+	float *input_buffer;
+	int input_buffer_size;
+	int encoded_pts;
+	int encoded_duration;
+} EncoderContext;
+
+EMSCRIPTEN_KEEPALIVE
+EncoderContext *init_encoder(int channels, int sample_rate, int bitrate) {
+	av_log_set_level(AV_LOG_ERROR);
+
+	const AVCodec *codec = avcodec_find_encoder(AV_CODEC_ID_AAC);
+	if (!codec) return NULL;
+
+	AVCodecContext *codec_ctx = avcodec_alloc_context3(codec);
+	if (!codec_ctx) return NULL;
+
+	codec_ctx->sample_fmt = AV_SAMPLE_FMT_FLTP;
+	codec_ctx->sample_rate = sample_rate;
+	codec_ctx->bit_rate = bitrate;
+	codec_ctx->time_base = (AVRational){1, sample_rate};
+
+	AVChannelLayout layout;
+	av_channel_layout_default(&layout, channels);
+	av_channel_layout_copy(&codec_ctx->ch_layout, &layout);
+	av_channel_layout_uninit(&layout);
+
+	if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
+		avcodec_free_context(&codec_ctx);
+		return NULL;
+	}
+
+	AVPacket *packet = av_packet_alloc();
+	if (!packet) {
+		avcodec_free_context(&codec_ctx);
+		return NULL;
+	}
+
+	AVFrame *frame = av_frame_alloc();
+	if (!frame) {
+		av_packet_free(&packet);
+		avcodec_free_context(&codec_ctx);
+		return NULL;
+	}
+
+	frame->format = AV_SAMPLE_FMT_FLTP;
+	frame->sample_rate = sample_rate;
+	frame->nb_samples = codec_ctx->frame_size;
+	av_channel_layout_copy(&frame->ch_layout, &codec_ctx->ch_layout);
+
+	if (av_frame_get_buffer(frame, 0) < 0) {
+		av_frame_free(&frame);
+		av_packet_free(&packet);
+		avcodec_free_context(&codec_ctx);
+		return NULL;
+	}
+
+	EncoderContext *ctx = malloc(sizeof(EncoderContext));
+	if (!ctx) {
+		av_frame_free(&frame);
+		av_packet_free(&packet);
+		avcodec_free_context(&codec_ctx);
+		return NULL;
+	}
+
+	ctx->codec_ctx = codec_ctx;
+	ctx->packet = packet;
+	ctx->frame = frame;
+	ctx->input_buffer = NULL;
+	ctx->input_buffer_size = 0;
+	ctx->encoded_pts = 0;
+	ctx->encoded_duration = 0;
+
+	return ctx;
+}
+
+EMSCRIPTEN_KEEPALIVE
+int get_encoder_frame_size(EncoderContext *ctx) {
+	return ctx->codec_ctx->frame_size;
+}
+
+EMSCRIPTEN_KEEPALIVE
+uint8_t *get_encoder_extradata(EncoderContext *ctx) {
+	return ctx->codec_ctx->extradata;
+}
+
+EMSCRIPTEN_KEEPALIVE
+int get_encoder_extradata_size(EncoderContext *ctx) {
+	return ctx->codec_ctx->extradata_size;
+}
+
+EMSCRIPTEN_KEEPALIVE
+float *get_encode_input_ptr(EncoderContext *ctx, int size) {
+	if (ctx->input_buffer_size < size) {
+		free(ctx->input_buffer);
+		ctx->input_buffer = malloc(size);
+		if (!ctx->input_buffer) {
+			ctx->input_buffer_size = 0;
+			return NULL;
+		}
+		ctx->input_buffer_size = size;
+	}
+	return ctx->input_buffer;
+}
+
+EMSCRIPTEN_KEEPALIVE
+int send_frame(EncoderContext *ctx, int pts) {
+	int channels = ctx->codec_ctx->ch_layout.nb_channels;
+	int frame_size = ctx->frame->nb_samples;
+
+	ctx->frame->pts = pts;
+
+	// Deinterleave f32 input into the frame's f32-planar planes
+	float *input = ctx->input_buffer;
+	for (int ch = 0; ch < channels; ch++) {
+		float *plane = (float *)ctx->frame->data[ch];
+		for (int i = 0; i < frame_size; i++) {
+			plane[i] = input[i * channels + ch];
+		}
+	}
+
+	return avcodec_send_frame(ctx->codec_ctx, ctx->frame);
+}
+
+EMSCRIPTEN_KEEPALIVE
+int receive_packet(EncoderContext *ctx) {
+	int ret = avcodec_receive_packet(ctx->codec_ctx, ctx->packet);
+	if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
+		return 0;
+	}
+	if (ret < 0) return ret;
+
+	ctx->encoded_pts = ctx->packet->pts;
+	ctx->encoded_duration = ctx->packet->duration;
+
+	return ctx->packet->size;
+}
+
+EMSCRIPTEN_KEEPALIVE
+void flush_encoder_start(EncoderContext *ctx) {
+	avcodec_send_frame(ctx->codec_ctx, NULL);
+}
+
+EMSCRIPTEN_KEEPALIVE
+void reset_encoder(EncoderContext *ctx) {
+	avcodec_flush_buffers(ctx->codec_ctx);
+}
+
+EMSCRIPTEN_KEEPALIVE
+uint8_t *get_encoded_data(EncoderContext *ctx) {
+	return ctx->packet->data;
+}
+
+EMSCRIPTEN_KEEPALIVE
+int get_encoded_pts(EncoderContext *ctx) {
+	return ctx->encoded_pts;
+}
+
+EMSCRIPTEN_KEEPALIVE
+int get_encoded_duration(EncoderContext *ctx) {
+	return ctx->encoded_duration;
+}
+
+EMSCRIPTEN_KEEPALIVE
+void close_encoder(EncoderContext *ctx) {
+	free(ctx->input_buffer);
+	av_frame_free(&ctx->frame);
+	av_packet_free(&ctx->packet);
+	avcodec_free_context(&ctx->codec_ctx);
+	free(ctx);
+}

packages/aac-encoder/src/encode.worker.ts

@@ -0,0 +1,204 @@
+/*!
+ * Copyright (c) 2026-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 createModule from '../build/aac';
+import type { WorkerCommand, WorkerResponse, WorkerResponseData } from './shared';
+
+type ExtendedEmscriptenModule = EmscriptenModule & {
+	cwrap: typeof cwrap;
+};
+
+let module: ExtendedEmscriptenModule;
+let modulePromise: Promise<ExtendedEmscriptenModule> | null = null;
+
+let initEncoderFn: (channels: number, sampleRate: number, bitrate: number) => number;
+let getEncoderFrameSize: (ctx: number) => number;
+let getEncoderExtradata: (ctx: number) => number;
+let getEncoderExtradataSize: (ctx: number) => number;
+let getEncodeInputPtr: (ctx: number, size: number) => number;
+let sendFrameFn: (ctx: number, pts: number) => number;
+let receivePacketFn: (ctx: number) => number;
+let flushEncoderStartFn: (ctx: number) => void;
+let resetEncoderFn: (ctx: number) => void;
+let getEncodedData: (ctx: number) => number;
+let getEncodedPts: (ctx: number) => number;
+let getEncodedDuration: (ctx: number) => number;
+let closeEncoderFn: (ctx: number) => void;
+
+const ensureModule = async () => {
+	if (!module) {
+		if (modulePromise) {
+			return modulePromise;
+		}
+
+		modulePromise = createModule() as Promise<ExtendedEmscriptenModule>;
+		module = await modulePromise;
+		modulePromise = null;
+
+		initEncoderFn = module.cwrap('init_encoder', 'number', ['number', 'number', 'number']);
+		getEncoderFrameSize = module.cwrap('get_encoder_frame_size', 'number', ['number']);
+		getEncoderExtradata = module.cwrap('get_encoder_extradata', 'number', ['number']);
+		getEncoderExtradataSize = module.cwrap('get_encoder_extradata_size', 'number', ['number']);
+		getEncodeInputPtr = module.cwrap('get_encode_input_ptr', 'number', ['number', 'number']);
+		sendFrameFn = module.cwrap('send_frame', 'number', ['number', 'number']);
+		receivePacketFn = module.cwrap('receive_packet', 'number', ['number']);
+		flushEncoderStartFn = module.cwrap('flush_encoder_start', null, ['number']);
+		resetEncoderFn = module.cwrap('reset_encoder', null, ['number']);
+		getEncodedData = module.cwrap('get_encoded_data', 'number', ['number']);
+		getEncodedPts = module.cwrap('get_encoded_pts', 'number', ['number']);
+		getEncodedDuration = module.cwrap('get_encoded_duration', 'number', ['number']);
+		closeEncoderFn = module.cwrap('close_encoder', null, ['number']);
+	}
+};
+
+const initEncoder = async (
+	numberOfChannels: number,
+	sampleRate: number,
+	bitrate: number,
+) => {
+	await ensureModule();
+
+	const ctx = initEncoderFn(numberOfChannels, sampleRate, bitrate);
+	if (ctx === 0) {
+		throw new Error('Failed to initialize AAC encoder.');
+	}
+
+	const frameSize = getEncoderFrameSize(ctx);
+
+	const extradataPtr = getEncoderExtradata(ctx);
+	const extradataSize = getEncoderExtradataSize(ctx);
+	const extradata = module.HEAPU8.slice(extradataPtr, extradataPtr + extradataSize).buffer;
+
+	return { ctx, frameSize, extradata };
+};
+
+type PacketInfo = { encodedData: ArrayBuffer; pts: number; duration: number };
+
+const drainPackets = (ctx: number) => {
+	const packets: PacketInfo[] = [];
+
+	let size: number;
+	while ((size = receivePacketFn(ctx)) > 0) {
+		const ptr = getEncodedData(ctx);
+		const encodedData = module.HEAPU8.slice(ptr, ptr + size).buffer;
+		const pts = getEncodedPts(ctx);
+		const duration = getEncodedDuration(ctx);
+		packets.push({ encodedData, pts, duration });
+	}
+
+	return packets;
+};
+
+const encode = (ctx: number, audioData: ArrayBuffer, timestamp: number) => {
+	const audioBytes = new Uint8Array(audioData);
+
+	const inputPtr = getEncodeInputPtr(ctx, audioBytes.length);
+	if (inputPtr === 0) {
+		throw new Error('Failed to allocate encoder input buffer.');
+	}
+	module.HEAPU8.set(audioBytes, inputPtr);
+
+	const ret = sendFrameFn(ctx, timestamp);
+	if (ret < 0) {
+		throw new Error(`Encode failed with error code ${ret}.`);
+	}
+
+	return drainPackets(ctx);
+};
+
+const onMessage = (data: { id: number; command: WorkerCommand }) => {
+	const { id, command } = data;
+
+	const handleCommand = async (): Promise<void> => {
+		try {
+			let result: WorkerResponseData;
+			const transferables: Transferable[] = [];
+
+			switch (command.type) {
+				case 'init': {
+					const { ctx, frameSize, extradata } = await initEncoder(
+						command.data.numberOfChannels,
+						command.data.sampleRate,
+						command.data.bitrate,
+					);
+					result = { type: command.type, ctx, frameSize, extradata };
+					transferables.push(extradata);
+				}; break;
+
+				case 'encode': {
+					const packets = encode(
+						command.data.ctx,
+						command.data.audioData,
+						command.data.timestamp,
+					);
+					for (const p of packets) {
+						transferables.push(p.encodedData);
+					}
+					result = { type: command.type, packets };
+				}; break;
+
+				case 'flush': {
+					flushEncoderStartFn(command.data.ctx);
+					const packets = drainPackets(command.data.ctx);
+					for (const p of packets) {
+						transferables.push(p.encodedData);
+					}
+					resetEncoderFn(command.data.ctx);
+					result = { type: command.type, packets };
+				}; break;
+
+				case 'close': {
+					closeEncoderFn(command.data.ctx);
+					result = { type: command.type };
+				}; break;
+			}
+
+			const response: WorkerResponse = {
+				id,
+				success: true,
+				data: result,
+			};
+			sendMessage(response, transferables);
+		} catch (error: unknown) {
+			const response: WorkerResponse = {
+				id,
+				success: false,
+				error,
+			};
+			sendMessage(response);
+		}
+	};
+
+	void handleCommand();
+};
+
+const sendMessage = (data: unknown, transferables?: Transferable[]) => {
+	if (parentPort) {
+		parentPort.postMessage(data, transferables ?? []);
+	} else {
+		self.postMessage(data, { transfer: transferables ?? [] });
+	}
+};
+
+let parentPort: {
+	postMessage: (data: unknown, transferables?: Transferable[]) => void;
+	on: (event: string, listener: (data: never) => void) => void;
+} | null = null;
+
+if (typeof self === 'undefined') {
+	const workerModule = 'worker_threads';
+	// eslint-disable-next-line @stylistic/max-len
+	// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment, @typescript-eslint/no-require-imports, @typescript-eslint/no-unsafe-member-access
+	parentPort = require(workerModule).parentPort;
+}
+
+if (parentPort) {
+	parentPort.on('message', onMessage);
+} else {
+	self.addEventListener('message', event => onMessage(event.data as { id: number; command: WorkerCommand }));
+}

packages/aac-encoder/src/encoder.ts

@@ -0,0 +1,306 @@
+/*!
+ * Copyright (c) 2026-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 {
+	type AdtsHeaderTemplate,
+	buildAdtsHeaderTemplate,
+	parseAacAudioSpecificConfig,
+	writeAdtsFrameLength,
+} from '../../../shared/aac-misc';
+import {
+	CustomAudioEncoder,
+	AudioCodec,
+	AudioSample,
+	EncodedPacket,
+	registerEncoder,
+} from 'mediabunny';
+import type { WorkerCommand, WorkerResponse, WorkerResponseData } from './shared';
+// @ts-expect-error An esbuild plugin handles this, TypeScript doesn't need to understand
+import createWorker from './encode.worker';
+
+const AAC_SAMPLE_RATES = [
+	96000, 88200, 64000, 48000, 44100, 32000,
+	24000, 22050, 16000, 12000, 11025, 8000, 7350,
+];
+
+class AacEncoder extends CustomAudioEncoder {
+	private worker: Worker | null = null;
+	private nextMessageId = 0;
+	private pendingMessages = new Map<number, {
+		resolve: (value: WorkerResponseData) => void;
+		reject: (reason?: unknown) => void;
+	}>();
+
+	private ctx = 0;
+	private encoderFrameSize = 0;
+	private sampleRate = 0;
+	private numberOfChannels = 0;
+	private chunkMetadata: EncodedAudioChunkMetadata = {};
+	private useAdts = false;
+	private adtsHeaderTemplate: AdtsHeaderTemplate | null = null;
+	private description: Uint8Array | null = null;
+
+	// Accumulate interleaved f32 samples until we have a full frame
+	private pendingBuffer = new Float32Array(2 ** 16);
+	private pendingFrames = 0;
+	private nextSampleTimestampInSamples: number | null = null;
+	private nextPacketTimestampInSamples: number | null = null;
+
+	static override supports(codec: AudioCodec, config: AudioEncoderConfig): boolean {
+		return codec === 'aac'
+			&& config.numberOfChannels >= 1
+			&& config.numberOfChannels <= 8
+			&& AAC_SAMPLE_RATES.includes(config.sampleRate)
+			&& config.bitrate !== undefined;
+	}
+
+	async init() {
+		// eslint-disable-next-line @typescript-eslint/no-unsafe-call
+		this.worker = (await createWorker()) as Worker;
+
+		const onMessage = (data: WorkerResponse) => {
+			const pending = this.pendingMessages.get(data.id);
+			assert(pending !== undefined);
+
+			this.pendingMessages.delete(data.id);
+			if (data.success) {
+				pending.resolve(data.data);
+			} else {
+				pending.reject(data.error);
+			}
+		};
+
+		if (this.worker.addEventListener) {
+			this.worker.addEventListener('message', event => onMessage(event.data as WorkerResponse));
+		} else {
+			const nodeWorker = this.worker as unknown as {
+				on: (event: string, listener: (data: never) => void) => void;
+			};
+			nodeWorker.on('message', onMessage);
+		}
+
+		assert(this.config.bitrate !== undefined);
+		this.sampleRate = this.config.sampleRate;
+		this.numberOfChannels = this.config.numberOfChannels;
+
+		const result = await this.sendCommand({
+			type: 'init',
+			data: {
+				numberOfChannels: this.config.numberOfChannels,
+				sampleRate: this.config.sampleRate,
+				bitrate: this.config.bitrate,
+			},
+		});
+
+		this.ctx = result.ctx;
+		this.encoderFrameSize = result.frameSize;
+
+		// The ffmpeg encoder provides an AudioSpecificConfig as extradata after init
+		const description = new Uint8Array(result.extradata);
+
+		const aacConfig = (this.config as { aac?: { format?: 'aac' | 'adts' } }).aac;
+		this.useAdts = aacConfig?.format === 'adts';
+
+		if (this.useAdts) {
+			const audioSpecificConfig = parseAacAudioSpecificConfig(description);
+			this.adtsHeaderTemplate = buildAdtsHeaderTemplate(audioSpecificConfig);
+		}
+
+		this.description = this.useAdts ? null : description;
+		this.resetInternalState();
+	}
+
+	private resetInternalState() {
+		this.pendingFrames = 0;
+		this.nextSampleTimestampInSamples = null;
+		this.nextPacketTimestampInSamples = null;
+
+		this.chunkMetadata = {
+			decoderConfig: {
+				codec: 'mp4a.40.2',
+				numberOfChannels: this.config.numberOfChannels,
+				sampleRate: this.config.sampleRate,
+				...(this.description ? { description: this.description } : {}),
+			},
+		};
+	}
+
+	async encode(audioSample: AudioSample) {
+		if (this.nextSampleTimestampInSamples === null) {
+			this.nextSampleTimestampInSamples = Math.round(audioSample.timestamp * this.sampleRate);
+			this.nextPacketTimestampInSamples = this.nextSampleTimestampInSamples;
+		}
+
+		const channels = this.numberOfChannels;
+		const incomingFrames = audioSample.numberOfFrames;
+
+		// Extract interleaved f32 data
+		const totalBytes = audioSample.allocationSize({ format: 'f32', planeIndex: 0 });
+		const audioBytes = new Uint8Array(totalBytes);
+		audioSample.copyTo(audioBytes, { format: 'f32', planeIndex: 0 });
+		const incomingData = new Float32Array(audioBytes.buffer);
+
+		const requiredSamples = (this.pendingFrames + incomingFrames) * channels;
+		if (requiredSamples > this.pendingBuffer.length) {
+			let newSize = this.pendingBuffer.length;
+			while (newSize < requiredSamples) {
+				newSize *= 2;
+			}
+			const newBuffer = new Float32Array(newSize);
+			newBuffer.set(this.pendingBuffer.subarray(0, this.pendingFrames * channels));
+			this.pendingBuffer = newBuffer;
+		}
+		this.pendingBuffer.set(incomingData, this.pendingFrames * channels);
+		this.pendingFrames += incomingFrames;
+
+		while (this.pendingFrames >= this.encoderFrameSize) {
+			await this.encodeOneFrame();
+		}
+	}
+
+	async flush() {
+		// Pad remaining samples with silence to fill a full frame
+		if (this.pendingFrames > 0) {
+			const channels = this.numberOfChannels;
+			const frameSize = this.encoderFrameSize;
+			const usedSamples = this.pendingFrames * channels;
+			const frameSamples = frameSize * channels;
+
+			this.pendingBuffer.fill(0, usedSamples, frameSamples);
+			this.pendingFrames = frameSize;
+
+			await this.encodeOneFrame();
+		}
+
+		const result = await this.sendCommand({ type: 'flush', data: { ctx: this.ctx } });
+		this.emitPackets(result.packets);
+
+		this.resetInternalState();
+	}
+
+	close() {
+		void this.sendCommand({ type: 'close', data: { ctx: this.ctx } });
+		this.worker?.terminate();
+	}
+
+	private async encodeOneFrame() {
+		assert(this.nextSampleTimestampInSamples !== null);
+		assert(this.nextPacketTimestampInSamples !== null);
+
+		const channels = this.numberOfChannels;
+		const frameSize = this.encoderFrameSize;
+		const frameSamples = frameSize * channels;
+
+		const frameData = this.pendingBuffer.slice(0, frameSamples);
+
+		// Shift remaining using copyWithin
+		this.pendingFrames -= frameSize;
+		if (this.pendingFrames > 0) {
+			this.pendingBuffer.copyWithin(0, frameSamples, frameSamples + this.pendingFrames * channels);
+		}
+
+		const audioData = frameData.buffer;
+		const result = await this.sendCommand({
+			type: 'encode',
+			data: {
+				ctx: this.ctx,
+				audioData,
+				timestamp: this.nextSampleTimestampInSamples,
+			},
+		}, [audioData]);
+
+		this.nextSampleTimestampInSamples += frameSize;
+
+		this.emitPackets(result.packets);
+	}
+
+	private emitPackets(packets: Array<{ encodedData: ArrayBuffer; pts: number; duration: number }>) {
+		assert(this.nextPacketTimestampInSamples !== null);
+
+		for (const p of packets) {
+			let data = new Uint8Array(p.encodedData);
+
+			if (this.useAdts) {
+				assert(this.adtsHeaderTemplate !== null);
+				const { header, bitstream } = this.adtsHeaderTemplate;
+				const frameLength = header.byteLength + data.byteLength;
+				writeAdtsFrameLength(bitstream, frameLength);
+
+				const adtsFrame = new Uint8Array(frameLength);
+				adtsFrame.set(header, 0);
+				adtsFrame.set(data, header.byteLength);
+				data = adtsFrame;
+			}
+
+			const packet = new EncodedPacket(
+				data,
+				'key',
+				this.nextPacketTimestampInSamples / this.sampleRate,
+				p.duration / this.sampleRate,
+			);
+
+			this.nextPacketTimestampInSamples += p.duration;
+
+			this.onPacket(
+				packet,
+				this.chunkMetadata,
+			);
+
+			this.chunkMetadata = {};
+		}
+	}
+
+	private sendCommand<T extends string>(
+		command: WorkerCommand & { type: T },
+		transferables?: Transferable[],
+	) {
+		return new Promise<WorkerResponseData & { type: T }>((resolve, reject) => {
+			const id = this.nextMessageId++;
+			this.pendingMessages.set(id, {
+				resolve: resolve as (value: WorkerResponseData) => void,
+				reject,
+			});
+
+			assert(this.worker);
+
+			if (transferables) {
+				this.worker.postMessage({ id, command }, transferables);
+			} else {
+				this.worker.postMessage({ id, command });
+			}
+		});
+	}
+}
+
+/**
+ * Registers the AAC encoder, which Mediabunny will then use automatically when applicable. Make sure to call this
+ * function before starting any encoding task.
+ *
+ * Preferably, wrap the call in a condition to avoid overriding any native AAC encoder:
+ *
+ * ```ts
+ * import { canEncodeAudio } from 'mediabunny';
+ * import { registerAacEncoder } from '@mediabunny/aac-encoder';
+ *
+ * if (!(await canEncodeAudio('aac'))) {
+ *     registerAacEncoder();
+ * }
+ * ```
+ *
+ * @group \@mediabunny/aac-encoder
+ * @public
+ */
+export const registerAacEncoder = () => {
+	registerEncoder(AacEncoder);
+};
+
+function assert(x: unknown): asserts x {
+	if (!x) {
+		throw new Error('Assertion failed.');
+	}
+}

packages/aac-encoder/src/index.ts

@@ -0,0 +1,20 @@
+/*!
+ * Copyright (c) 2026-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/.
+ */
+
+const AAC_ENCODER_LOADED_SYMBOL = Symbol.for('@mediabunny/aac-encoder loaded');
+if ((globalThis as Record<symbol, unknown>)[AAC_ENCODER_LOADED_SYMBOL]) {
+	console.error(
+		'[WARNING]\n@mediabunny/aac-encoder was loaded twice.'
+		+ ' This will likely cause the encoder not to work correctly.'
+		+ ' Check if multiple dependencies are importing different versions of @mediabunny/aac-encoder,'
+		+ ' or if something is being bundled incorrectly.',
+	);
+}
+(globalThis as Record<symbol, unknown>)[AAC_ENCODER_LOADED_SYMBOL] = true;
+
+export { registerAacEncoder } from './encoder';

packages/aac-encoder/src/shared.ts

@@ -0,0 +1,66 @@
+/*!
+ * Copyright (c) 2026-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/.
+ */
+
+export type WorkerCommand = {
+	type: 'init';
+	data: {
+		numberOfChannels: number;
+		sampleRate: number;
+		bitrate: number;
+	};
+} | {
+	type: 'encode';
+	data: {
+		ctx: number;
+		audioData: ArrayBuffer;
+		timestamp: number;
+	};
+} | {
+	type: 'flush';
+	data: {
+		ctx: number;
+	};
+} | {
+	type: 'close';
+	data: {
+		ctx: number;
+	};
+};
+
+export type WorkerResponseData = {
+	type: 'init';
+	ctx: number;
+	frameSize: number;
+	extradata: ArrayBuffer;
+} | {
+	type: 'encode';
+	packets: Array<{
+		encodedData: ArrayBuffer;
+		pts: number;
+		duration: number;
+	}>;
+} | {
+	type: 'flush';
+	packets: Array<{
+		encodedData: ArrayBuffer;
+		pts: number;
+		duration: number;
+	}>;
+} | {
+	type: 'close';
+};
+
+export type WorkerResponse = {
+	id: number;
+} & ({
+	success: true;
+	data: WorkerResponseData;
+} | {
+	success: false;
+	error: unknown;
+});