[mythtv] 8902 HD transcode => MPEG4 --> a/v out of sync
jcrews at gridlox.net
Thu Feb 9 02:52:16 UTC 2006
I've been having an issue with transcoding anything recorded from a
particular ATSC transponder (NBC affiiliate, OTA). The output always
shows the video somewhere around .5 seconds earlier than the audio.
Maybe even an entire second.
Anyway, I'd like to try to figure this one out, but I'm not too sure as
to how to go about isolating the area that has to be enhanced/fixed.
All other local transponders have good transcode output.
I did run mythtranscode with mpeg2fix process messages enabled, and
nothing came out. NVP did throw at me an "Guessing at a/v sync values"
message, which, according to the comment, is indicitive of something
terribly, terribly wrong in the source file. In this case, it looks
like the NBC station is transmitting a funky stream. The a/v sync is
wrong early in the output, so I'm sure something is breaking at a
When I play the file back via mythfrontend, it also throws the guess
message, but the A/V sync is correct. What could be different in the
way that NVP calls are being utiized by mythfrontend vs. mpeg2fix in
mythtranscode? There are some comments in there about how some
operations being done "might not be a good idea."
Should I add some messages to print aPTS, vPTS, PCR (really, whatever
the PCR is equivalent to in a TS), and try to see where drift is being
There does appear to be some logic to figure out if the above values
are wrong, and I recieved no such messages.
Thanks for any advice. Regards,
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