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Created by Marianna Smidth Buschle@msb.qtec

mpegtsmux: backwards DTS when segment changes

See https://github.com/RidgeRun/gst-interpipe/issues/96#issuecomment-893431600

Basically I'm playing with some pipelines using x264enc and mpegtsmux.

This works fine:

GST_DEBUG="*:3" gst-launch-1.0 v4l2src ! videoconvert ! x264enc key-int-max=30 speed-preset=1 tune=zerolatency ! video/x-h264,profile=high ! h264parse ! mpegtsmux name=mux ! rtpmp2tpay ! udpsink port=7000 host=127.0.0.1 sync=0

But then when I add the interpipe elements from RidgeRun I start getting:0:00:00.729042661 192147 0x56175b8f50c0 WARN basetsmux gstbasetsmux.c:1608:gst_base_ts_mux_clip:<mux:sink_0> ignoring DTS going backward

GST_DEBUG="*:3" gst-launch-1.0 v4l2src ! videoconvert ! x264enc key-int-max=30 speed-preset=1 tune=zerolatency ! video/x-h264,profile=high ! h264parse ! interpipesink name=video_out sync=false async=false interpipesrc name=mux_V listen-to=video_out is-live=true stream-sync=passthrough-ts format=time ! h264parse ! mpegtsmux name=mux ! rtpmp2tpay ! udpsink port=7000 host=127.0.0.1 sync=0

From what I was able to debug the problem seems to be that without the interpipe the mpegtsmux only receives 1 segment event, which comes from the encoder (and contains the x264 1000 hours offset):

Inspect Event: <enum GST_EVENT_SEGMENT of type Gst.EventType> pad: enc_out::src
Segment: 
Base:0.0 Duration: 18446744073.709553 Format: <enum GST_FORMAT_TIME of type Gst.Format> Offset: 0.0 Position: 3599999.699365496
Start: 3599999.699365496 Stop: 18446744073.709553 Time: 0.0
to_running_time: 0

Inspect Event: <enum GST_EVENT_SEGMENT of type Gst.EventType> pad: mux_out::sink_0
Segment: 
Base:0.0 Duration: 18446744073.709553 Format: <enum GST_FORMAT_TIME of type Gst.Format> Offset: 0.0 Position: 3599999.699365496
Start: 3599999.699365496 Stop: 18446744073.709553 Time: 0.0
to_running_time: 0

But when I add the interpipe it gets 2 segment events, the 1st without the x264 offset and the 2nd with:

Inspect Event: <enum GST_EVENT_SEGMENT of type Gst.EventType> pad: enc_out::src
Segment: 
Base:0.0 Duration: 18446744073.709553 Format: <enum GST_FORMAT_TIME of type Gst.Format> Offset: 0.0 Position: 3599999.699365496
Start: 3599999.699365496 Stop: 18446744073.709553 Time: 0.0
to_running_time: 0

Inspect Event: <enum GST_EVENT_SEGMENT of type Gst.EventType> pad: mux_out::sink_0
Segment: 
Base:0.0 Duration: 18446744073.709553 Format: <enum GST_FORMAT_TIME of type Gst.Format> Offset: 0.0 Position: 0.0
Start: 0.0 Stop: 18446744073.709553 Time: 0.0
to_running_time: 0

Inspect Event: <enum GST_EVENT_SEGMENT of type Gst.EventType> pad: mux_out::sink_0
Segment: 
Base:0.0 Duration: 18446744073.709553 Format: <enum GST_FORMAT_TIME of type Gst.Format> Offset: 0.0 Position: 3599999.699365496
Start: 3599999.699365496 Stop: 18446744073.709553 Time: 0.0
to_running_time: 0

And then the mpegtsmux starts its execution using the 1st segment, which gives a DTS of +1000:00:00, and later when it starts calculating the DTS with the new segment (which removes the offset) it gets smaller than the initial one and therefore keeps getting ignored...

https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/blob/master/gst/mpegtsmux/gstbasetsmux.c#L1696

Maybe this check should be ignored or updated if there was a segment change?