[mythtv] Ticket #9410: Positioning problems with BBC HD and BBC ONE HD recordings

[Taylor Ralph]

On Sun, Jan 2, 2011 at 9:36 AM, Paul Gardiner <lists at glidos.net> wrote:
> On 01/01/2011 18:35, MythTV wrote:
>>
>> #9410: Positioning problems with BBC HD and BBC ONE HD recordings
>> -------------------------------------+-----------------------------
>>  Reporter:  mythtv@…                 |          Owner:  janne
>>      Type:  Bug Report               |         Status:  assigned
>>  Priority:  minor                    |      Milestone:  unknown
>> Component:  MythTV - Video Playback  |        Version:  Unspecified
>>  Severity:  medium                   |     Resolution:
>>  Keywords:                           |  Ticket locked:  0
>> -------------------------------------+-----------------------------
>>
>> Comment (by jpoet):
>>
>>  When trying to detect a "new" access unit (AU), one of the things to look
>>  for is a change in the nal_ref_idc value.
>>
>>  nal_ref_idc is part of '''every''' NAL UNIT, and we are currently testing
>>  to see if it changed for '''every''' NAL UNIT.  Re-reading
>>  T-REC-H.264-200711-I!!PDF-E.pdf, I don't think that is correct.  When
>>  looking for a "new" AU, the nal_ref_idc should only be tested when the
>>  current NAL UNIT is a "slice".
>>
>>  I have attached a patch which makes this change.  I have tested it with
>>  HD-PVR recordings, and it does not seem to cause anything bad to happen.
>>
>>  It would be nice if someone else would read the spec to see if they
>>  interpret it the same way.
>
> I've partially tried the patch, in that I've rebuilt mythtv on my
> backend with the patch included, and then regenerated positions maps
> for some of my recordings using mythcommflag --rebuild. I haven't
> rebuilt myth on my frontend yet because I use minimyth, and building
> it from scratch can take 10 hours, plus I'll need to remind myself
> how to add patches to minimyth. The patch doesn't seem to have fixed
> the problem completely, but then again I don't know if you would expect
> it to have, or whether it need to be applied to both frontend and
> backend.
>
> I'm just rebuilding position maps for all my old BBC HD rercordings
> to see if the problem looks fixed for any of them.
>
> Cheers,
>        Paul.

The patch you are trying will not fix the issue. It's a problem John
Poet found with the h264 parser when debugging the problem. He has
since discovered what is most likely the root cause of the bad pos
map. It appears that BBC is sending FU-A and FU-B type RTP packets
that our parser currently ignores. Parsing for these type of packets
will most likely need to be added to properly support these new
broadcasts streams.

Regards.
--
Taylor