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Make ADTS demuxer spit out ADTS packets instead of AAC, make ADTS muxer accept both AAC and ADTS input

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Vanilagy
2026-01-14 13:52:46 +01:00
parent 06ab9c8433
commit 045df3b9a5
6 changed files with 242 additions and 61 deletions
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src/adts/adts-muxer.ts
+52 -33
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@@ -7,7 +7,7 @@
*/
import { AacAudioSpecificConfig, parseAacAudioSpecificConfig, validateAudioChunkMetadata } from '../codec';
import { assert, Bitstream, toUint8Array } from '../misc';
import { Bitstream, toUint8Array } from '../misc';
import { Muxer } from '../muxer';
import { Output, OutputAudioTrack } from '../output';
import { AdtsOutputFormat } from '../output-format';
@@ -20,6 +20,7 @@ export class AdtsMuxer extends Muxer {
private header = new Uint8Array(7);
private headerBitstream = new Bitstream(this.header);
private audioSpecificConfig: AacAudioSpecificConfig | null = null;
private inputIsAdts: boolean | null = null;
constructor(output: Output, format: AdtsOutputFormat) {
super(output);
@@ -52,49 +53,67 @@ export class AdtsMuxer extends Muxer {
try {
this.validateAndNormalizeTimestamp(track, packet.timestamp, packet.type === 'key');
if (!this.audioSpecificConfig) {
if (this.inputIsAdts === null) {
validateAudioChunkMetadata(meta);
const description = meta?.decoderConfig?.description;
assert(description);
this.audioSpecificConfig = parseAacAudioSpecificConfig(toUint8Array(description));
// From the WebCodecs Codec Registry:
// "If description is present, it is assumed to a AudioSpecificConfig as defined in [iso14496-3] section
// 1.6.2.1, Table 1.15, and the bitstream is assumed to be in aac.
// If the description is not present, the bitstream is assumed to be in adts format."
this.inputIsAdts = !description;
const { objectType, frequencyIndex, channelConfiguration } = this.audioSpecificConfig;
const profile = objectType - 1;
if (!this.inputIsAdts) {
this.audioSpecificConfig = parseAacAudioSpecificConfig(toUint8Array(description!));
this.headerBitstream.writeBits(12, 0b1111_11111111); // Syncword
this.headerBitstream.writeBits(1, 0); // MPEG Version
this.headerBitstream.writeBits(2, 0); // Layer
this.headerBitstream.writeBits(1, 1); // Protection absence
this.headerBitstream.writeBits(2, profile); // Profile
this.headerBitstream.writeBits(4, frequencyIndex); // MPEG-4 Sampling Frequency Index
this.headerBitstream.writeBits(1, 0); // Private bit
this.headerBitstream.writeBits(3, channelConfiguration); // MPEG-4 Channel Configuration
this.headerBitstream.writeBits(1, 0); // Originality
this.headerBitstream.writeBits(1, 0); // Home
this.headerBitstream.writeBits(1, 0); // Copyright ID bit
this.headerBitstream.writeBits(1, 0); // Copyright ID start
this.headerBitstream.skipBits(13); // Frame length
this.headerBitstream.writeBits(11, 0x7ff); // Buffer fullness
this.headerBitstream.writeBits(2, 0); // Number of AAC frames minus 1
// Omit CRC check
const { objectType, frequencyIndex, channelConfiguration } = this.audioSpecificConfig;
const profile = objectType - 1;
this.headerBitstream.writeBits(12, 0b1111_11111111); // Syncword
this.headerBitstream.writeBits(1, 0); // MPEG Version
this.headerBitstream.writeBits(2, 0); // Layer
this.headerBitstream.writeBits(1, 1); // Protection absence
this.headerBitstream.writeBits(2, profile); // Profile
this.headerBitstream.writeBits(4, frequencyIndex); // MPEG-4 Sampling Frequency Index
this.headerBitstream.writeBits(1, 0); // Private bit
this.headerBitstream.writeBits(3, channelConfiguration); // MPEG-4 Channel Configuration
this.headerBitstream.writeBits(1, 0); // Originality
this.headerBitstream.writeBits(1, 0); // Home
this.headerBitstream.writeBits(1, 0); // Copyright ID bit
this.headerBitstream.writeBits(1, 0); // Copyright ID start
this.headerBitstream.skipBits(13); // Frame length
this.headerBitstream.writeBits(11, 0x7ff); // Buffer fullness
this.headerBitstream.writeBits(2, 0); // Number of AAC frames minus 1
// Omit CRC check
}
}
const frameLength = packet.data.byteLength + this.header.byteLength;
this.headerBitstream.pos = 30;
this.headerBitstream.writeBits(13, frameLength);
if (this.inputIsAdts) {
// Packets are already ADTS frames, write them directly
const startPos = this.writer.getPos();
this.writer.write(packet.data);
const startPos = this.writer.getPos();
this.writer.write(this.header);
this.writer.write(packet.data);
if (this.format._options.onFrame) {
this.format._options.onFrame(packet.data, startPos);
}
} else {
// Packets are raw AAC, prepend ADTS header
const frameLength = packet.data.byteLength + this.header.byteLength;
this.headerBitstream.pos = 30;
this.headerBitstream.writeBits(13, frameLength);
if (this.format._options.onFrame) {
const frameBytes = new Uint8Array(frameLength);
frameBytes.set(this.header, 0);
frameBytes.set(packet.data, this.header.byteLength);
const startPos = this.writer.getPos();
this.writer.write(this.header);
this.writer.write(packet.data);
this.format._options.onFrame(frameBytes, startPos);
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();