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Fix incorrectly processed timestamps for fragmented MP4

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This commit is contained in:
Vanilagy
2025-06-07 18:54:19 +02:00
parent 0359a7f2b1
commit f5a56e1f62
3 changed files with 53 additions and 13 deletions
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src/isobmff/isobmff-muxer.ts
+34 -6
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@@ -37,6 +37,7 @@ export type Sample = {
};
type Chunk = {
/** The lowest presentation timestamp in this chunk */
startTimestamp: number;
samples: Sample[];
offset: number | null;
@@ -592,7 +593,7 @@ export class IsobmffMuxer extends Muxer {
return sample;
}
private processTimestamps(trackData: IsobmffTrackData) {
private processTimestamps(trackData: IsobmffTrackData, nextSample?: Sample) {
if (trackData.timestampProcessingQueue.length === 0) {
return;
}
@@ -725,9 +726,29 @@ export class IsobmffMuxer extends Muxer {
}
trackData.timestampProcessingQueue.length = 0;
assert(trackData.lastSample);
assert(trackData.lastTimescaleUnits !== null);
if (nextSample !== undefined && trackData.lastSample.timescaleUnitsToNextSample === 0) {
assert(nextSample.type === 'key');
// Given the next sample, we can make a guess about the duration of the last sample. This avoids having
// the last sample's duration in each fragment be "0" for fragmented files. The guess we make here is
// actually correct most of the time, since typically, no delta frame with a lower timestamp follows the key
// frame (although it can happen).
const timescaleUnits = intoTimescale(nextSample.timestamp, trackData.timescale, false);
const delta = Math.round(timescaleUnits - trackData.lastTimescaleUnits);
trackData.lastSample.timescaleUnitsToNextSample = delta;
}
}
private async registerSample(trackData: IsobmffTrackData, sample: Sample) {
if (sample.type === 'key') {
this.processTimestamps(trackData, sample);
}
trackData.timestampProcessingQueue.push(sample);
if (this.isFragmented) {
trackData.sampleQueue.push(sample);
await this.interleaveSamples();
@@ -737,10 +758,6 @@ export class IsobmffMuxer extends Muxer {
}
private async addSampleToTrack(trackData: IsobmffTrackData, sample: Sample) {
if (sample.type === 'key') {
this.processTimestamps(trackData);
}
if (!this.isFragmented) {
trackData.samples.push(sample);
}
@@ -749,6 +766,13 @@ export class IsobmffMuxer extends Muxer {
if (!trackData.currentChunk) {
beginNewChunk = true;
} else {
// Timestamp don't need to be monotonic (think B-frames), so we may need to update the start timestamp of
// the chunk
trackData.currentChunk.startTimestamp = Math.min(
trackData.currentChunk.startTimestamp,
sample.timestamp,
);
const currentChunkDuration = sample.timestamp - trackData.currentChunk.startTimestamp;
if (this.isFragmented) {
@@ -795,7 +819,6 @@ export class IsobmffMuxer extends Muxer {
assert(trackData.currentChunk);
trackData.currentChunk.samples.push(sample);
trackData.timestampProcessingQueue.push(sample);
if (this.isFragmented) {
this.maxWrittenTimestamp = Math.max(this.maxWrittenTimestamp, sample.timestamp);
@@ -1003,6 +1026,11 @@ export class IsobmffMuxer extends Muxer {
if (this.isFragmented) {
await this.interleaveSamples(true);
for (const trackData of this.trackDatas) {
this.processTimestamps(trackData);
}
await this.finalizeFragment(false); // Don't flush the last fragment as we will flush it with the mfra box
} else {
for (const trackData of this.trackDatas) {