[mythtv-commits] Ticket #12196: Invalid bitrate from AVFormat can stall reads from the RingBuffer

[MythTV]

#12196: Invalid bitrate from AVFormat can stall reads from the RingBuffer
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     Reporter:  david.madsen@…        |      Owner:
         Type:  Bug Report - General  |     Status:  new
     Priority:  minor                 |  Milestone:  unknown
    Component:  MythTV - General      |    Version:  Unspecified
     Severity:  medium                |   Keywords:
Ticket locked:  0                     |
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 I've had trouble recently with some recordings that can't be played back
 in the frontend or commflagged.

 The bitrate returned from AVFormat is incorrect because of a glitch near
 the end of the recording which reset the PTS near the end.  This cause
 AVFormat to have an entirely invalid bitrate, which was then propagated to
 the RingBuffer via the following code:

 AVFormatDecoder::ScanStreams() in libmythtv/avformatdecoder.cpp

 {{{
     if (ic && ((uint)ic->bit_rate > bitrate))
         bitrate = (uint)ic->bit_rate;

     if (bitrate > 0)
     {
         bitrate = (bitrate + 999) / 1000;
         if (ringBuffer)
             ringBuffer->UpdateRawBitrate(bitrate);
     }
 }}}

 This ended up setting the fill_min in the RingBuffer larger than the full
 size of the buffer, and consequently blocking reads from the RingBuffer
 since this condition never becomes true:

 {{{
         if ((0 == read_return) || (numfailures > 5) ||
             (readsallowed != (used >= fill_min || ateof ||
                               setswitchtonext || commserror)))
         {
 }}}

 I've attached a patch where I just capped the bitrate returned from
 AVFormat to exclude the erroneous values, though I'm not sure that's the
 best way to fix the problem.  Maybe a safeguard in the RingBuffer itself
 on the value of fill_min would be a better method.

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Ticket URL: <https://code.mythtv.org/trac/ticket/12196>
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