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Add segment start to adjusted buffer PTS #398

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Merged
milos-lk merged 3 commits into from
Nov 17, 2025
Merged

Add segment start to adjusted buffer PTS #398

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2c24cdd
Add segment start to adjusted buffer PTS
milos-lk Nov 17, 2025
266504f
Simplifying event probe
milos-lk Nov 17, 2025
76059ab
A small comment on the flow
milos-lk Nov 17, 2025
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2 changes: 1 addition & 1 deletion pkg/media/input.go
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Original file line number Diff line number Diff line change
Expand Up @@ -241,7 +241,7 @@ func (i *Input) onPadAdded(_ *gst.Element, pad *gst.Pad) {
state := timingState
i.registerGatePad(padName, state)
i.addGateProbe(pad, padName, state)
i.addSegmentEventProbe(pad, padName)
i.addSegmentEventProbe(pad, padName, state)
}

// Gather bitrate stats & attach latency meta from the pipeline
Expand Down
60 changes: 23 additions & 37 deletions pkg/media/input_gate.go
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,8 @@ type padTimingState struct {
windowStreamAccum time.Duration
windowElapsedAccum time.Duration
steadyWindowCount int

segmentStart atomic.Duration
}

func (i *Input) addGateProbe(pad *gst.Pad, padName string, state *padTimingState) {
Expand Down Expand Up @@ -96,50 +98,29 @@ func (i *Input) addGateProbe(pad *gst.Pad, padName string, state *padTimingState
})
}

func (i *Input) addSegmentEventProbe(pad *gst.Pad, padName string) {
logSegmentEvent := func(direction string, seg *gst.Segment) {
if seg == nil {
logger.Debugw("nil segment event received", "pad", padName, "direction", direction)
return
}

fields := []interface{}{
"pad", padName,
"direction", direction,
"format", seg.GetFormat(),
"rate", seg.GetRate(),
"appliedRate", seg.GetAppliedRate(),
"base", seg.GetBase(),
"start", seg.GetStart(),
"stop", seg.GetStop(),
"time", seg.GetTime(),
"position", seg.GetPosition(),
}

if seg.GetFormat() == gst.FormatTime {
fields = append(fields,
"baseDur", time.Duration(seg.GetBase()),
"startDur", time.Duration(seg.GetStart()),
"stopDur", time.Duration(seg.GetStop()),
"timeDur", time.Duration(seg.GetTime()),
"positionDur", time.Duration(seg.GetPosition()),
)
}

logger.Debugw("segment event received", fields...)
}

func (i *Input) addSegmentEventProbe(pad *gst.Pad, padName string, state *padTimingState) {
pad.AddProbe(gst.PadProbeTypeEventDownstream, func(_ *gst.Pad, info *gst.PadProbeInfo) gst.PadProbeReturn {
event := info.GetEvent()
if event == nil {
if event == nil || event.Type() != gst.EventTypeSegment {
return gst.PadProbeOK
}

switch event.Type() {
case gst.EventTypeSegment:
logSegmentEvent("downstream", event.ParseSegment())
seg := event.ParseSegment()
if seg == nil {
logger.Debugw("segment event missing data", "pad", padName)
return gst.PadProbeOK
}

state.segmentStart.Store(time.Duration(seg.GetStart()))
logger.Debugw("segment event received",
"pad", padName,
"format", seg.GetFormat(),
"start", seg.GetStart(),
"startDur", time.Duration(seg.GetStart()),
"time", seg.GetTime(),
"timeDur", time.Duration(seg.GetTime()),
"rate", seg.GetRate(),
)
return gst.PadProbeOK
})
}
Expand Down Expand Up @@ -292,6 +273,11 @@ func applyPadOffset(buffer *gst.Buffer, state *padTimingState, pts time.Duration
return false
}

// by design, every buffer must be preceded by SEGMENT (and SEGMENT is sticky),
// so downstream elements will push STREAM_START → CAPS → SEGMENT before any buffers.
// By the time buffers are processed, the segment start time will be set.
adj += state.segmentStart.Load()
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@biglittlebigben biglittlebigben Nov 17, 2025

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Can you comment on the flow here? Are we certain applyPadOffset always gets called after addSegmentEventProbe?

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@milos-lk milos-lk Nov 17, 2025

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yes - by design every buffer must be preceded by SEGMENT (and SEGMENT is sticky), so downstream elements will push STREAM_START → CAPS → SEGMENT before any buffers. Adding a short comment

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@milos-lk milos-lk Nov 17, 2025

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added the comment


buffer.SetPresentationTimestamp(gst.ClockTime(adj))
return true
}
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