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feat(codec): add detection support for AC-3, E-AC-3 audio codecs (#275)

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* ac3/eac3 detection

* fix tests

* review pass + follow codebase comments style

* Add ac3/eac3 to docs

* WIP mpeg-2

* Set registration_descriptor

* add support for ac3 system b in mpeg-ts

* Update docs with ac3 in .ts support

* fix formatting

* Remove default to fix linter

* Add eac3 to mpeg-ts

* fix formatting

* Fix failing test

* Refactor AC3/EAC3 code a little

---------

Co-authored-by: Vanilagy <[email protected]>
This commit is contained in:
jepcd
2026-02-11 15:23:12 +01:00
committed by GitHub
co-authored by Vanilagy
parent 612642c5ad
commit 417c85d8ed
24 changed files with 1061 additions and 16 deletions
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src/isobmff/isobmff-demuxer.ts
+54
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@@ -27,6 +27,11 @@ import {
FlacBlockType,
HevcDecoderConfigurationRecord,
Vp9CodecInfo,
parseEac3Config,
getEac3SampleRate,
getEac3ChannelCount,
AC3_SAMPLE_RATES,
AC3_ACMOD_CHANNEL_COUNTS,
} from '../codec-data';
import { Demuxer } from '../demuxer';
import { Input } from '../input';
@@ -952,6 +957,10 @@ export class IsobmffDemuxer extends Demuxer {
track.info.codec = 'ulaw';
} else if (lowercaseBoxName === 'alaw') {
track.info.codec = 'alaw';
} else if (lowercaseBoxName === 'ac-3') {
track.info.codec = 'ac3';
} else if (lowercaseBoxName === 'ec-3') {
track.info.codec = 'eac3';
} else {
console.warn(`Unsupported audio codec (sample entry type '${sampleBoxInfo.name}').`);
}
@@ -1463,6 +1472,51 @@ export class IsobmffDemuxer extends Demuxer {
track.info.codecDescription = description;
}; break;
case 'dac3': { // AC3SpecificBox
const track = this.currentTrack;
if (!track) {
break;
}
assert(track.info?.type === 'audio');
const bytes = readBytes(slice, 3);
const bitstream = new Bitstream(bytes);
const fscod = bitstream.readBits(2);
bitstream.skipBits(5 + 3); // Skip bsid and bsmod
const acmod = bitstream.readBits(3);
const lfeon = bitstream.readBits(1);
if (fscod < 3) {
track.info.sampleRate = AC3_SAMPLE_RATES[fscod]!;
}
track.info.numberOfChannels = AC3_ACMOD_CHANNEL_COUNTS[acmod]! + lfeon;
}; break;
case 'dec3': { // EC3SpecificBox
const track = this.currentTrack;
if (!track) {
break;
}
assert(track.info?.type === 'audio');
const bytes = readBytes(slice, boxInfo.contentSize);
const config = parseEac3Config(bytes);
if (!config) {
console.warn('Invalid dec3 box contents, ignoring.');
break;
}
const sampleRate = getEac3SampleRate(config);
if (sampleRate !== null) {
track.info.sampleRate = sampleRate;
}
track.info.numberOfChannels = getEac3ChannelCount(config);
}; break;
case 'stts': {
const track = this.currentTrack;
if (!track) {