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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/mpeg-ts/mpeg-ts-muxer.ts
+56 -7
View File
@@ -9,11 +9,13 @@
import { parseAacAudioSpecificConfig, validateAudioChunkMetadata, validateVideoChunkMetadata } from '../codec';
import { buildAdtsHeaderTemplate, writeAdtsFrameLength } from '../adts/adts-misc';
import {
AC3_REGISTRATION_DESCRIPTOR,
AvcDecoderConfigurationRecord,
AvcNalUnitType,
concatNalUnitsInAnnexB,
deserializeAvcDecoderConfigurationRecord,
deserializeHevcDecoderConfigurationRecord,
EAC3_REGISTRATION_DESCRIPTOR,
extractNalUnitTypeForAvc,
extractNalUnitTypeForHevc,
HevcDecoderConfigurationRecord,
@@ -151,11 +153,34 @@ export class MpegTsMuxer extends Muxer {
assert(meta?.decoderConfig);
const codec = track.source._codec;
assert(codec === 'aac' || codec === 'mp3');
assert(codec === 'aac' || codec === 'mp3' || codec === 'ac3' || codec === 'eac3');
let streamType: MpegTsStreamType;
let streamId: number;
switch (codec) {
case 'aac': {
streamType = MpegTsStreamType.AAC;
streamId = AUDIO_STREAM_ID_BASE + this.audioTrackIndex++;
}; break;
case 'mp3': {
streamType = MpegTsStreamType.MP3_MPEG1;
streamId = AUDIO_STREAM_ID_BASE + this.audioTrackIndex++;
}; break;
case 'ac3': {
streamType = MpegTsStreamType.AC3_SYSTEM_A;
streamId = 0xbd;
}; break;
case 'eac3': {
streamType = MpegTsStreamType.EAC3_SYSTEM_A;
streamId = 0xbd;
}; break;
}
const streamType = codec === 'aac' ? MpegTsStreamType.AAC : MpegTsStreamType.MP3_MPEG1;
const pid = FIRST_TRACK_PID + this.trackDatas.length;
const streamId = AUDIO_STREAM_ID_BASE + this.audioTrackIndex++;
const newTrackData: MpegTsTrackData = {
track,
@@ -373,7 +398,7 @@ export class MpegTsMuxer extends Muxer {
): Uint8Array {
const codec = (trackData.track as OutputAudioTrack).source._codec;
if (codec === 'mp3') {
if (codec === 'mp3' || codec === 'ac3' || codec === 'eac3') {
// We're good
return packet.data;
}
@@ -695,7 +720,18 @@ const PAT_SECTION = new Uint8Array(16);
}
const buildPmt = (trackDatas: MpegTsTrackData[]) => {
const sectionLength = 9 + trackDatas.length * 5 + 4;
let totalEsBytes = 0;
for (const trackData of trackDatas) {
totalEsBytes += 5;
if (trackData.streamType === MpegTsStreamType.AC3_SYSTEM_A) {
totalEsBytes += AC3_REGISTRATION_DESCRIPTOR.length;
} else if (trackData.streamType === MpegTsStreamType.EAC3_SYSTEM_A) {
totalEsBytes += EAC3_REGISTRATION_DESCRIPTOR.length;
}
}
const sectionLength = 9 + totalEsBytes + 4;
const section = new Uint8Array(3 + sectionLength - 4);
const view = toDataView(section);
@@ -714,8 +750,21 @@ const buildPmt = (trackDatas: MpegTsTrackData[]) => {
section[offset++] = trackData.streamType; // stream_type
view.setUint16(offset, 0xE000 | (trackData.pid & 0x1FFF), false); // reserved=111, elementary_PID
offset += 2;
view.setUint16(offset, 0xF000, false); // reserved=1111, ES_info_length=0
offset += 2;
if (trackData.streamType === MpegTsStreamType.AC3_SYSTEM_A) {
view.setUint16(offset, 0xF000 | AC3_REGISTRATION_DESCRIPTOR.length, false);
offset += 2;
section.set(AC3_REGISTRATION_DESCRIPTOR, offset);
offset += AC3_REGISTRATION_DESCRIPTOR.length;
} else if (trackData.streamType === MpegTsStreamType.EAC3_SYSTEM_A) {
view.setUint16(offset, 0xF000 | EAC3_REGISTRATION_DESCRIPTOR.length, false);
offset += 2;
section.set(EAC3_REGISTRATION_DESCRIPTOR, offset);
offset += EAC3_REGISTRATION_DESCRIPTOR.length;
} else {
view.setUint16(offset, 0xF000, false); // reserved=1111, ES_info_length=0
offset += 2;
}
}
const crc = computeMpegTsCrc32(section);