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Implement MP3 muxer

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Vanilagy
2025-01-26 11:45:56 +01:00
parent 7205d9445b
commit d3566305df
11 changed files with 482 additions and 148 deletions
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src/mp3/mp3-reader.ts
+5 -96
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@@ -1,44 +1,6 @@
import { assert } from '../misc';
import { Reader } from '../reader';
const FRAME_HEADER_SIZE = 4;
// These are in kbps:
const MPEG_V1_BITRATES: Record<number, number[]> = {
// Layer 3
1: [-1, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, -1],
// Layer 2
2: [-1, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, -1],
// Layer 1
3: [-1, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, -1],
};
const MPEG_V2_BITRATES: Record<number, number[]> = {
// Layer 3
1: [-1, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, -1],
// Layer 2
2: [-1, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, -1],
// Layer 1
3: [-1, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, -1],
};
const SAMPLING_RATES: Record<number, number[]> = {
// MPEG Version 2.5
0: [11025, 12000, 8000, -1],
// MPEG Version 2 (ISO/IEC 13818-3)
2: [22050, 24000, 16000, -1],
// MPEG Version 1 (ISO/IEC 11172-3)
3: [44100, 48000, 32000, -1],
};
export type FrameHeader = {
startPos: number;
mpegVersionId: number;
bitrate: number;
sampleRate: number;
channelCount: number;
totalSize: number;
dataStart: number;
dataSize: number;
};
import { FRAME_HEADER_SIZE, FrameHeader, readFrameHeader } from './mp3-misc';
export class Mp3Reader {
pos = 0;
@@ -96,66 +58,13 @@ export class Mp3Reader {
until ??= this.fileSize;
while (this.pos < until - FRAME_HEADER_SIZE) {
const startPos = this.pos;
const word = this.readU32();
this.pos -= 4;
const firstByte = word >>> 24;
const secondByte = (word >>> 16) & 0xff;
const thirdByte = (word >>> 8) & 0xff;
const fourthByte = word & 0xff;
if (firstByte !== 0xff && secondByte !== 0xff && thirdByte !== 0xff && fourthByte !== 0xff) {
continue;
const header = readFrameHeader(word, this);
if (header) {
return header;
}
this.pos -= 3; // For when we continue
if ((secondByte & 0xe0) !== 0xe0) {
continue;
}
const mpegVersionId = (secondByte >> 3) & 0x3;
const layer = (secondByte >> 1) & 0x3;
const bitrateIndex = (thirdByte >> 4) & 0xf;
const frequencyIndex = (thirdByte >> 2) & 0x3;
const padding = (thirdByte >> 1) & 0x1;
const channel = (fourthByte >> 6) & 0x3;
const kilobitRate = mpegVersionId === 3
? MPEG_V1_BITRATES[layer]?.[bitrateIndex]
: MPEG_V2_BITRATES[layer]?.[bitrateIndex];
if (!kilobitRate || kilobitRate === -1) {
continue;
}
const bitrate = kilobitRate * 1000;
const sampleRate = SAMPLING_RATES[mpegVersionId]?.[frequencyIndex];
if (!sampleRate || sampleRate === -1) {
continue;
}
const channelCount = channel === 3 ? 1 : 2;
const frameLength = Math.floor((144 * bitrate / sampleRate) + padding);
if (this.fileSize - startPos < frameLength) {
// The frame doesn't fit into the rest of the file
return null;
}
return {
startPos,
mpegVersionId,
bitrate,
sampleRate,
channelCount,
totalSize: frameLength,
dataStart: startPos + 4,
dataSize: frameLength - 4,
};
}
return null;