[gstreamer-bugs] [Bug 540215] New: decodebin does not insert a queue for raw data type

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-base | Ver: 0.10.19
           Summary: decodebin does not insert a queue for raw data type
           Product: GStreamer
           Version: 0.10.19
          Platform: Other
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: eugeni.stepanov at gmail.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


Please describe the problem:
Sometimes pipeline stalls. It always happens at the beginning of playback (in
prerolling stage) of a Matroska file with plaintext (S_TEXT/UTF8) subtitles
without a subtitle in the first few seconds. To reproduce, simply run playbin
with such file.

Decodebin inserts queue elements between a demuxer and a decoder. It keeps a
list of these queues. If one of them overflows, it is enlarged, BUT only if one
of the other queues is empty. The idea is (as I understand it), that if all the
queues are not empty the pipeline can proceed.

For this reason, it is very important that every path from the demuxer to the
outside of the bin contains at least one queue. If it is not the case, the
above condition (all queues but one are not empty) can not be checked
correctly.

For example, textoverlay processes video frames only if it has seen all the
earlier text frames. What happens?
1. The default video queue in decodebin is very short (8192 bytes) and it gets
overflown very quickly. 
2. Textoverlay has not seen enough text frames yet and cannot render. It has
read all the available text frames and is blocked in video_chain function.
3. Demuxer can not provide more text frames because it is blocked pushing video
frame into the overflown queue.
4. Decodebin knows that video queue is overflown but it does not enlarge it
because, surprise, all the other queues are not empty.

This happened because there is no queue in the text path. Demuxer provides a
text/plain pin and decodebin simply created a ghost pad for it.

The proposed solution is to insert a queue after pins that are currenly
directly mapped to ghost pads. They are the pins for with mimetype_is_raw() is
TRUE.

Steps to reproduce:
1. Get a file described earlier
2. Run it with playbin
3. Enjoy the silence


Actual results:
Pipeline blocks.

Expected results:
The file plays as intended.

Does this happen every time?
Yes. It might be not trivial to cook such file, because it has to have some
heavy video frames to overfill the queue in the first 0.5 seconds. After that,
matroskademux will send a NEWSEGMENT event, allowing textoverlay to progress.

Other information:


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