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feat(library): estimate flac and mp4 duration

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This commit is contained in:
Timur Cravtov 2026-03-06 22:06:12 +02:00
parent 8c7a7547c9
commit 6545b31388
1 changed files with 52 additions and 0 deletions
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52
js/metadata.js
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@ -134,6 +134,7 @@ async function readFlacMetadata(file, metadata) {
const blocks = parseFlacBlocks(dataView);
const vorbisBlock = blocks.find((b) => b.type === 4);
const pictureBlock = blocks.find((b) => b.type === 6);
const streamInfo = blocks.find((b) => b.type === 0);
const artists = [];
if (vorbisBlock) {
@ -166,6 +167,30 @@ async function readFlacMetadata(file, metadata) {
}
}
if (streamInfo) {
const offset = streamInfo.offset;
// Sample Rate is 20 bits spanning bytes 10, 11, and the first 4 bits of 12
const byte10 = dataView.getUint8(offset + 10);
const byte11 = dataView.getUint8(offset + 11);
const byte12 = dataView.getUint8(offset + 12);
// since data for some reason spans across multiple bytes, we need to combine them into one int
const sampleRate = (byte10 << 12) | (byte11 << 4) | (byte12 >> 4);
const byte13 = dataView.getUint8(offset + 13);
const tsHigh = byte13 & 0x0f;
const tsLow = dataView.getUint32(offset + 14, false);
// same thing for total samples
const totalSamples = (tsHigh * 0x100000000) + tsLow;
if (sampleRate > 0) {
// beatiful
metadata.duration = totalSamples / sampleRate;
}
}
if (artists.length > 0) {
metadata.artists = artists.flatMap((a) => a.split(/; |\/|\\/)).map((name) => ({ name: name.trim() }));
}
@ -212,6 +237,33 @@ async function readM4aMetadata(file, metadata) {
const udta = moovAtoms.find((a) => a.type === 'udta');
if (!udta) return;
// mvhd metadata tag
const mvhd = moovAtoms.find((a) => a.type === 'mvhd');
if (mvhd) {
const mvhdStart = moovStart + mvhd.offset + 8;
const version = view.getUint8(mvhdStart);
// resolution and length, basically
let timeScale, duration;
if (version === 0) {
// 32-bit format
timeScale = view.getUint32(mvhdStart + 12, false);
duration = view.getUint32(mvhdStart + 16, false);
} else if (version === 1) {
// 64-bit format
timeScale = view.getUint32(mvhdStart + 20, false);
const durHigh = view.getUint32(mvhdStart + 24, false);
const durLow = view.getUint32(mvhdStart + 28, false);
duration = (durHigh * 0x100000000) + durLow;
}
if (timeScale > 0) {
metadata.duration = duration / timeScale;
}
}
const udtaStart = moovStart + udta.offset + 8;
const udtaLen = udta.size - 8;
const udtaData = new DataView(view.buffer, udtaStart, udtaLen);