[Bug 763336] New: [mpegtsmux] subtitle stream is always selected for PCR

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=763336

            Bug ID: 763336
           Summary: [mpegtsmux] subtitle stream is always selected for PCR
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: vincent.genieux at startigen.fr
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Created attachment 323423
  --> https://bugzilla.gnome.org/attachment.cgi?id=323423&action=edit
avoid using a sparse stream in PCR selection

When using mpegtsmux, it appears that the subtitle pad is almost always chosen
by the element as a PCR reference which is not really a good idea (audio or
video stream would be a better idea to avoid latencies when muxing live
streams).

This bug is reproducible with gst-launch-1.0 on git/master (+ patch from
#759807) with a pipeline such as :

filesrc ! tsdemux name=d mpegtsmux name=m ! filesink d.video_0078 ! queue !
mpegvideoparse ! avdec_mpeg2video ! deinterlace ! videoscale !
video/x-raw,width=320,height=240 ! x264enc bitrate=1024 ! h264parse ! m.
d.audio_0082 ! queue ! mpegaudioparse ! avdec_mp2float ! audioconvert !
voaacenc ! aacparse ! m. d.subpicture_008d ! queue ! subpicture/x-dvb ! m.
d.subpicture_008e ! queue ! subpicture/x-dvb ! m

When using GST_DEBUG=mpegtsmux:5, we can see in the logs :
mpegtsmux.c:1188:mpegtsmux_collected_buffer:<m> Pads collected
mpegtsmux.c:598:mpegtsmux_create_stream:<m:sink_65> Creating stream with PID
0x0041 for caps video/x-h264, [...]
mpegtsmux.c:598:mpegtsmux_create_stream:<m:sink_66> Creating stream with PID
0x0042 for caps audio/mpeg, [...]
mpegtsmux.c:598:mpegtsmux_create_stream:<m:sink_67> Creating stream with PID
0x0043 for caps audio/mpeg, [...]
mpegtsmux.c:598:mpegtsmux_create_stream:<m:sink_68> Creating stream with PID
0x0044 for caps audio/mpeg, [...]
mpegtsmux.c:598:mpegtsmux_create_stream:<m:sink_69> Creating stream with PID
0x0045 for caps subpicture/x-dvb
mpegtsmux.c:598:mpegtsmux_create_stream:<m:sink_70> Creating stream with PID
0x0046 for caps subpicture/x-dvb
mpegtsmux.c:1271:mpegtsmux_collected_buffer:<m:sink_69> Use stream (pid=69)
from pad as PCR for program (prog_id = 0)


-> see latest log line choosing sink_69 with caps subpicture/x-dvb

The proposed patch delay the PCR selection until the stream is not sparse.

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