[mythtv] XVideo XvMC VLD broken

[Terry Barnaby]

Hi,

My investigations into this are leading to the fact that there is a bug
in the MPEG TS handling in libavformat or libavcodecs. At least when
XvMC VLD is involved but possibly in all cases although other decoding
methods my cope with the bug better.

What "appears" to happen is that when the PMT changes is that the
AVCODEC for the old stream starts calling XVMC_VLD_field_end() multiple
times intertwined with the new stream starting to send valid MPEG streams
and hence calling XVMC_VLD_field_start(), XVMC_VLD_decode_slice() ...
XVMC_VLD_field_end(). This messes up the hardware decoding when
XVMC_VLD_field_end() appears out of order.

I also notice that when a stream is removed in av_remove_stream():2099
it manages its list of streams by moving up a complex data structure
with a memmove() routine. This is a potentialy very dangerous thing
to do with complex data structures containing pointers etc etc ...

Can anyone give me a run down on what actually is suposed to happen
when a channel is changed in MythTv when using DVB and TS streams ?

I would have expected someting like:

DVB -> MPEGTS -> VideoCodec -> Sync -> Video Out
               -> AudioCodec -> Sync -> Audio Out

I would have though that all that would need changing would be
the DVB system selecting different PID's and possibly re-tuning, then
MPEGTS selecting the different streams. The Video out should not need
any changes (aprat from size changes which would be being handled already).
Is this the case ??
Ant pointers to the higher levels of code where the channel change is
implemented ??

Terry