[mythtv] 8902 HD transcode => MPEG4 --> a/v out of sync

[Jesse Crews]

I'm renewing this thread because I've found the cause of this issue. 
The A/V sync mismatch always happens when the original video has 6 
channels. I originally thought it was the station, but that was only a 
coincidence, as it happens to be the only one that I record 6 channel 
audio from. The offset that I have to put into the adjust a/v sync 
option is -300ms to get it back to where it looks correct. I use 6 
channel pass through, so the original plays with the correct sync.

Ok, please bear with me. :)

Where's the AC3 -> 2ch -> WAV happening? There seems to be a fault 
there, causing timing (aPTS?) values to be 300ms off. I have tested 
several recordings, and the same setting brings the a/v back in sync.

I don't know anything about AC3, but mplayer always says that it's a 2 
channel 48KHz  stream as far as the hardware is concerned. Could this 
be somehow confusing the transcoder?

I've looked at avformatdecoder.cpp, and NuppelVideoRecorder.cpp. I 
could not find any direct references to AC3/ac3 in NVR.

Would a direct stream copy option be difficult to implement, so 
transcoded files have ac3 audio?

Regards,
Jesse


Quoting Geoffrey Hausheer <mythtv0368 at phracturedblue.com>:

> On 2/9/06, Jesse Crews wrote:
>> Oops, something got mixed up in my mind after reading transcode.cpp. :)
>> It's mpeg2->mpeg4. mpeg2fix is not actually being created here.
> Well, at ths point, I can't really help you much.  While I did a lot
> of work on the original MPEG4 transcoder, that was several years ago,
> and I really haven't looked at it since.  I no longer can use MPEG4,
> and only have the bandwidth to help with MPEG2->MPEG2 transcoding
> (i.e. mpeg2fix).  The logs you sent me aren't very useful (I guess we
> never had the need for the kind of issues we run into in mpeg2fix, so
> the logging isn't as robust).  I guess your best bet would be to just
> file a ticket and keep the problematic mpeg stream around for testing.
> You could try running it trough 'mythtranscode --mpeg' first, which
> might clean up any problems in the stream, and then transcode to
> MPEG4, but that is more of a possible work-around than a solution.
>
> .Geoff
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