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Track keyframe gap to prevent flush cascades

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Add LastKeyframeGapMs to MP4 state and update fragment-flush logic to consider the previous keyframe gap before forcing a fragment boundary. Previously any unexpectedly short keyframe gap (< MinNormalGOPMs) would force a flush, which could cascade on streams that legitimately emit short GOPs. Now we only force a flush when the current gap is short and the prior gap was healthy (or unset), and we record the current gap for future checks. Also refactor the check to use a local gap variable and preserve the existing log message.
This commit is contained in:
Cédric Verstraeten
2026-05-12 15:54:48 +02:00
parent 860acd3a6e
commit 8ea84d87db
1 changed files with 18 additions and 7 deletions
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25
machinery/src/video/mp4.go
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@@ -66,6 +66,7 @@ type MP4 struct {
FragmentStartRawPTS uint64 // Raw PTS for timing when to flush fragments
FragmentStartDTS uint64 // Accumulated VideoTotalDuration at fragment start (matches tfdt)
LastKeyframeRawPTS uint64 // Raw PTS of the most recently seen keyframe (in any fragment)
LastKeyframeGapMs uint64 // Gap (ms) between the previous two consecutive keyframes
MoofBoxes int64 // Number of moof boxes in the file
MoofBoxSizes []int64 // Sizes of each moof box
SegmentDurations []uint64 // Duration of each segment in timescale units
@@ -326,13 +327,23 @@ func (mp4 *MP4) AddSampleToTrack(trackID uint32, isKeyframe bool, data []byte, p
// fragment with a "media corruption" error because the inner IDR resets
// frame_num/POC inside what they expect to be a single GOP. Force a
// fragment boundary whenever two consecutive keyframes arrive much
// closer than a normal GOP (here: < 500 ms apart). This isolates the
// seam IDR into its own fragment so each fragment stays a clean GOP.
if !shouldFlush && trackID == uint32(mp4.VideoTrack) && mp4.Start &&
mp4.LastKeyframeRawPTS > 0 && pts > mp4.LastKeyframeRawPTS &&
pts-mp4.LastKeyframeRawPTS < MinNormalGOPMs {
log.Log.Warning(fmt.Sprintf("mp4.AddSampleToTrack(): forcing fragment flush at unexpectedly close keyframe (gap=%d ms, fragment elapsed=%d ms) - likely upstream loop/restart discontinuity", pts-mp4.LastKeyframeRawPTS, elapsed))
shouldFlush = true
// closer than a normal GOP.
//
// We only flag this as a seam when it is a *sudden* anomaly: the
// previous keyframe gap must have been healthy (>= MinNormalGOPMs).
// This avoids false positives on cameras that legitimately emit
// short-interval IDRs (short GOP, motion-triggered recovery IDRs,
// all-intra streams) where every keyframe would otherwise be flagged
// in a cascade, producing many tiny fragments and log spam.
if trackID == uint32(mp4.VideoTrack) && mp4.Start &&
mp4.LastKeyframeRawPTS > 0 && pts > mp4.LastKeyframeRawPTS {
gap := pts - mp4.LastKeyframeRawPTS
if !shouldFlush && gap < MinNormalGOPMs &&
(mp4.LastKeyframeGapMs == 0 || mp4.LastKeyframeGapMs >= MinNormalGOPMs) {
log.Log.Warning(fmt.Sprintf("mp4.AddSampleToTrack(): forcing fragment flush at unexpectedly close keyframe (gap=%d ms, fragment elapsed=%d ms) - likely upstream loop/restart discontinuity", gap, elapsed))
shouldFlush = true
}
mp4.LastKeyframeGapMs = gap
}
if trackID == uint32(mp4.VideoTrack) {
mp4.LastKeyframeRawPTS = pts