@mediabunny/ac3

Browsers have no support for AC-3 (Dolby Digital) or E-AC-3 (Dolby Digital Plus) in their WebCodecs implementations. This extension package provides both a decoder and encoder for use with Mediabunny, allowing you to decode and encode these codecs directly in the browser. It is implemented using Mediabunny's custom coder API and uses a fast, size-optimized WASM build of FFmpeg's AC-3 and E-AC-3 coders under the hood.

This package, like the rest of Mediabunny, is enabled by its sponsors and their donations. If you've derived value from this package, please consider leaving a donation! 💘

Installation

This library peer-depends on Mediabunny. Install both using npm:

npm install mediabunny @mediabunny/ac3

Alternatively, directly include them using a script tag:

<script src="mediabunny.js"></script>
<script src="mediabunny-ac3.js"></script>

This will expose the global objects Mediabunny and MediabunnyAc3. Use mediabunny-ac3.d.ts to provide types for these globals. You can download the built distribution files from the releases page.

Usage

import { registerAc3Decoder, registerAc3Encoder } from '@mediabunny/ac3';

registerAc3Decoder();
registerAc3Encoder();

That's it - Mediabunny now uses the registered AC-3/E-AC-3 decoder and encoder automatically.

Building and development

For simplicity, all built WASM artifacts are included in the repo, since these rarely change. However, here are the instructions for building them from scratch:

Install Emscripten and clone FFmpeg. Then, from the Mediabunny root and with Emscripten sourced in:

export FFMPEG_PATH=/path/to/ffmpeg
export MEDIABUNNY_ROOT=$PWD

# Build FFmpeg
cd $FFMPEG_PATH
emmake make distclean
emconfigure ./configure \
    --target-os=none \
    --arch=x86_32 \
    --enable-cross-compile \
    --disable-asm \
    --disable-x86asm \
    --disable-inline-asm \
    --disable-programs \
    --disable-doc \
    --disable-debug \
    --disable-all \
    --disable-everything \
    --disable-autodetect \
    --disable-pthreads \
    --disable-runtime-cpudetect \
    --enable-avcodec \
    --enable-decoder=ac3 \
    --enable-decoder=eac3 \
    --enable-encoder=ac3 \
    --enable-encoder=eac3 \
    --cc="emcc" \
    --cxx=em++ \
    --ar=emar \
    --ranlib=emranlib \
    --extra-cflags="-DNDEBUG -Oz -flto -msimd128" \
    --extra-ldflags="-Oz -flto"
emmake make

# Compile the bridge between JavaScript and FFmpeg's API
cd $MEDIABUNNY_ROOT/packages/ac3
emcc src/bridge.c \
    $FFMPEG_PATH/libavcodec/libavcodec.a \
    $FFMPEG_PATH/libavutil/libavutil.a \
    -I$FFMPEG_PATH \
    -s MODULARIZE=1 \
    -s EXPORT_ES6=1 \
    -s SINGLE_FILE=1 \
    -s ALLOW_MEMORY_GROWTH=1 \
    -s ENVIRONMENT=web,worker \
    -s FILESYSTEM=0 \
    -s MALLOC=emmalloc \
    -s SUPPORT_LONGJMP=0 \
    -s EXPORTED_RUNTIME_METHODS=cwrap,HEAPU8 \
    -s EXPORTED_FUNCTIONS=_malloc,_free \
    -msimd128 \
    -flto \
    -Oz \
    -o build/ac3.js

This generates build/ac3.js, which contains both the JavaScript "glue code" as well as the compiled WASM inlined.

Building the package

Then, the complete JavaScript package can be built alongside the rest of Mediabunny by running npm run build in Mediabunny's root.