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Rewrite ADTS muxer to use Bitstream

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Ally
2025-08-18 22:47:43 +02:00
parent 8da619a624
commit 9054b8e381
1 changed files with 26 additions and 41 deletions
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src/adts/adts-muxer.ts
+26 -41
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@@ -7,7 +7,7 @@
*/
import { AacAudioSpecificConfig, parseAacAudioSpecificConfig, validateAudioChunkMetadata } from '../codec';
import { assert, toUint8Array } from '../misc';
import { assert, Bitstream, toUint8Array } from '../misc';
import { Muxer } from '../muxer';
import { Output, OutputAudioTrack } from '../output';
import { AdtsOutputFormat } from '../output-format';
@@ -18,6 +18,8 @@ export class AdtsMuxer extends Muxer {
private format: AdtsOutputFormat;
private writer: Writer;
private header = new Uint8Array(7);
private headerBitstream = new Bitstream(this.header);
private audioSpecificConfig: AacAudioSpecificConfig | null = null;
constructor(output: Output, format: AdtsOutputFormat) {
@@ -56,48 +58,31 @@ export class AdtsMuxer extends Muxer {
assert(description);
this.audioSpecificConfig = parseAacAudioSpecificConfig(toUint8Array(description));
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 syncword = 0b1111_11111111;
this.header[0] = (syncword >> 4);
const mpegVersion = 0;
const layer = 0;
const protectionAbsence = 1;
this.header[1] = (syncword << 4)
| (mpegVersion << 3)
| (layer << 1)
| protectionAbsence;
const privateBit = 0;
this.header[2] = (((this.audioSpecificConfig.objectType - 1) & 0b11) << 6)
| ((this.audioSpecificConfig.frequencyIndex & 0b1111) << 2)
| (privateBit << 1)
| ((this.audioSpecificConfig.channelConfiguration & 0b111) >> 2);
const originality = 0;
const homeUsage = 0;
const copyrightIdBit = 0;
const copyrightIdStart = 0;
const frameLength = (packet.data.byteLength + this.header.byteLength) & 0b11111_11111111;
this.header[3] = ((this.audioSpecificConfig.channelConfiguration & 0b111) << 6)
| (originality << 5)
| (homeUsage << 4)
| (copyrightIdBit << 3)
| (copyrightIdStart << 2)
| (frameLength >> 11);
this.header[4] = (frameLength >> 3);
const bufferFullness = 0x7ff; // Variable bitrate
this.header[5] = (frameLength << 5)
| (bufferFullness >> 6);
const numberOfAacFrames = 1;
this.header[6] = (bufferFullness << 2)
| (numberOfAacFrames - 1);
// Omit CRC check
const frameLength = packet.data.byteLength + this.header.byteLength;
this.headerBitstream.pos = 30;
this.headerBitstream.writeBits(13, frameLength);
const startPos = this.writer.getPos();
this.writer.write(this.header);