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Allow non-zero initial timestamps for ISOBMFF muxer

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Vanilagy
2025-01-04 14:02:45 +01:00
parent 2e8d49f900
commit 5bb9f8609c
7 changed files with 109 additions and 22 deletions
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src/isobmff/isobmff-muxer.ts
+13 -9
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@@ -85,8 +85,6 @@ export const intoTimescale = (timeInSeconds: number, timescale: number, round =
};
export class IsobmffMuxer extends Muxer {
override timestampsMustStartAtZero = true;
private writer: Writer;
private boxWriter: IsobmffBoxWriter;
private fastStart: NonNullable<Mp4OutputFormatOptions['fastStart']>;
@@ -263,10 +261,6 @@ export class IsobmffMuxer extends Muxer {
this.trackDatas.push(newTrackData);
this.trackDatas.sort((a, b) => a.track.id - b.track.id);
// Subtitle cues don't need to start at 0, so let's register a timestamp at 0 to satisfy the
// "timestamps must start a zero" constraint
this.validateAndNormalizeTimestamp(track, 0, true);
return newTrackData;
}
@@ -446,8 +440,7 @@ export class IsobmffMuxer extends Muxer {
data,
size: data.byteLength,
type,
// Will be refined once the next sample comes in
timescaleUnitsToNextSample: intoTimescale(duration, trackData.timescale),
timescaleUnitsToNextSample: intoTimescale(duration, trackData.timescale), // Will be refined
};
return sample;
@@ -469,6 +462,12 @@ export class IsobmffMuxer extends Muxer {
// model it.
sample.decodeTimestamp = sortedTimestamps[i]!;
if (this.fastStart !== 'fragmented' && trackData.lastTimescaleUnits === null) {
// In non-fragmented files, the first decode timestamp is always zero. If the first presentation
// timestamp isn't zero, we'll simply use the composition time offset to achieve it.
sample.decodeTimestamp = 0;
}
const sampleCompositionTimeOffset
= intoTimescale(sample.timestamp - sample.decodeTimestamp, trackData.timescale);
const durationInTimescale = intoTimescale(sample.duration, trackData.timescale);
@@ -533,7 +532,8 @@ export class IsobmffMuxer extends Muxer {
}
}
} else {
trackData.lastTimescaleUnits = 0;
// Decode timestamp of the first sample
trackData.lastTimescaleUnits = intoTimescale(sample.decodeTimestamp, trackData.timescale, false);
if (this.fastStart !== 'fragmented') {
trackData.timeToSampleTable.push({
@@ -581,6 +581,10 @@ export class IsobmffMuxer extends Muxer {
// We can only finalize this fragment (and begin a new one) if we know that each track will be able to
// start the new one with a key frame.
const keyFrameQueuedEverywhere = this.trackDatas.every((otherTrackData) => {
if (otherTrackData.track.source._closed) {
return true;
}
if (trackData === otherTrackData) {
return sample.type === 'key';
}