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Adjust MinNormalGOPMs threshold to prevent false positives on loop seams

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Cédric Verstraeten
2026-05-12 13:56:07 +00:00
parent 8ea84d87db
commit d3f53e4b6b
2 changed files with 22 additions and 10 deletions
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25
machinery/src/video/mp4.go
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@@ -32,14 +32,23 @@ const MacEpochOffset uint64 = 2082844800
// resulting in ~3 second fragments (assuming a typical GOP interval).
const FragmentDurationMs = 3000
// MinNormalGOPMs is the minimum spacing we expect between two consecutive
// IDRs of a healthy source (typical encoders produce IDRs every 1000ms or
// more). When two keyframes arrive closer than this, we treat the second one
// as an upstream restart/loop-seam and force a fresh fragment so the seam
// IDR cannot end up as a mid-fragment sync sample. The check only runs when
// the current fragment has not yet reached FragmentDurationMs, so it never
// fires during normal multi-GOP fragments at intended GOP boundaries.
const MinNormalGOPMs = 950
// MinNormalGOPMs is the maximum spacing between two consecutive IDRs that
// we still consider an anomalous "loop/restart seam". When two keyframes
// arrive closer than this, we treat the second one as an upstream
// restart/loop-seam and force a fresh fragment so the seam IDR cannot end
// up as a mid-fragment sync sample. The check only runs when the current
// fragment has not yet reached FragmentDurationMs.
//
// This must be set well below the smallest plausible *legitimate* GOP
// length. Typical IP cameras use GOP intervals of 1000-2000 ms, and the
// arrival timing of consecutive IDRs can jitter by a few hundred ms due to
// network/RTSP buffering. A threshold close to 1 s (e.g. 950) caused
// false positives on cameras with ~1 s GOPs (warnings like
// "gap=800 ms / 300 ms / 200 ms" while the stream itself was healthy).
// 400 ms is comfortably below any realistic GOP yet still catches the
// virtual-rtsp / ffmpeg loop-seam pattern (seam IDRs typically arrive
// 100-200 ms after the prior IDR).
const MinNormalGOPMs = 400
type MP4 struct {
// FileName is the name of the file

7
machinery/src/video/mp4_loopseam_test.go
View File

@@ -51,8 +51,11 @@ func TestMP4LoopSeamIsolation(t *testing.T) {
// 17 seconds of normal content (last "good" IDR at sec 17).
emit(17*30, 30)
// Seam: IDR arrives ~867ms after previous (vs normal 1000ms).
pts -= 100
// Seam: IDR arrives ~150ms after previous (vs normal ~1000ms).
// This matches the realistic virtual-rtsp / ffmpeg `-stream_loop`
// loop boundary, where the new clip's first IDR is emitted shortly
// after the previous clip's final IDR.
pts -= 820
emit(13*30, 30)
mp4Video.Close(&models.Config{Signing: &models.Signing{PrivateKey: ""}})