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Fix gaps introduced in video buffer by remuxer work-around #2894

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merged 1 commit into from Jul 16, 2020
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Fix gaps introduced in video buffer by remuxer work-around #2894

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27 changes: 14 additions & 13 deletions src/remux/mp4-remuxer.js
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Expand Up @@ -52,9 +52,12 @@ class MP4Remuxer {
// if first audio DTS is not aligned with first video DTS then we need to take that into account
// when providing timeOffset to remuxAudio / remuxVideo. if we don't do that, there might be a permanent / small
// drift between audio and video streams
let audiovideoDeltaDts = (audioTrack.samples[0].pts - videoTrack.samples[0].pts) / videoTrack.inputTimeScale;
audioTimeOffset += Math.max(0, audiovideoDeltaDts);
videoTimeOffset += Math.max(0, -audiovideoDeltaDts);
// Use pts at timeOffset 0 so that VOD streams begin at 0
const tsDelta = timeOffset > 0 ? audioTrack.samples[0].dts - videoTrack.samples[0].dts
: audioTrack.samples[0].pts - videoTrack.samples[0].pts;
const audiovideoTimestampDelta = tsDelta / videoTrack.inputTimeScale;
audioTimeOffset += Math.max(0, audiovideoTimestampDelta);
videoTimeOffset += Math.max(0, -audiovideoTimestampDelta);
}
// Purposefully remuxing audio before video, so that remuxVideo can use nextAudioPts, which is
// calculated in remuxAudio.
Expand Down Expand Up @@ -258,11 +261,16 @@ class MP4Remuxer {
firstDTS = inputSamples[0].dts;
lastDTS = inputSamples[nbSamples - 1].dts;

// on Safari let's signal the same sample duration for all samples
// sample duration (as expected by trun MP4 boxes), should be the delta between sample DTS
// set this constant duration as being the avg delta between consecutive DTS.
const averageSampleDuration = Math.round((lastDTS - firstDTS) / (nbSamples - 1));

// check timestamp continuity across consecutive fragments (this is to remove inter-fragment gap/hole)
const delta = firstDTS - nextAvcDts;
// if fragment are contiguous, detect hole/overlapping between fragments
if (contiguous) {
const foundHole = delta > 2;
const foundHole = delta > averageSampleDuration;
const foundOverlap = delta < -1;
if (foundHole || foundOverlap) {
if (foundHole) {
Expand All @@ -274,17 +282,10 @@ class MP4Remuxer {
minPTS -= delta;
inputSamples[0].dts = firstDTS;
inputSamples[0].pts = minPTS;
logger.log(`Video: PTS/DTS adjusted: ${toMsFromMpegTsClock(minPTS, true)}/${toMsFromMpegTsClock(firstDTS, true)}, delta: ${toMsFromMpegTsClock(delta, true)} ms`);
logger.log(`Video: First PTS/DTS adjusted: ${toMsFromMpegTsClock(minPTS, true)}/${toMsFromMpegTsClock(firstDTS, true)}, delta: ${toMsFromMpegTsClock(delta, true)} ms`);
}
}

// on Safari let's signal the same sample duration for all samples
// sample duration (as expected by trun MP4 boxes), should be the delta between sample DTS
// set this constant duration as being the avg delta between consecutive DTS.
if (isSafari) {
mp4SampleDuration = Math.round((lastDTS - firstDTS) / (nbSamples - 1));
}

// Clamp first DTS to 0 so that we're still aligning on initPTS,
// and not passing negative values to MP4.traf. This will change initial frame compositionTimeOffset!
firstDTS = Math.max(firstDTS, 0);
Expand All @@ -304,7 +305,7 @@ class MP4Remuxer {
// normalize PTS/DTS
if (isSafari) {
// sample DTS is computed using a constant decoding offset (mp4SampleDuration) between samples
sample.dts = firstDTS + i * mp4SampleDuration;
sample.dts = firstDTS + i * averageSampleDuration;
} else {
// ensure sample monotonic DTS
sample.dts = Math.max(sample.dts, firstDTS);
Expand Down