[mythtv] bttv recordings run fast

Joseph A. Caputo jcaputo1 at comcast.net
Fri Mar 5 10:27:39 EST 2004

On Friday 05 March 2004 09:58, bobnvic at everestkc.net wrote:
> I upgraded to cvs on 3/2/04 from cvs from early March and every
> recording on bttv card since then plays very fast.  The recording
> starts out playing normally for the first few seconds and then
> everything speeds up by a significant amount making it impossible to
> follow. Recordings from my PVR-250 card was unaffected.  The PVR-250
> mpeg2 files are automatically transcoded to mpeg4, while the bttv are
> recorded in mpeg4 and not transcoded.  I can view the files in
> windows using the ds filters and the files play fine.  I'm using the
> 0.7.x series of bttv drivers.
> Is there anything that I can provide that can help track down this
> issue?  The WAF dropped considerably after it happened the second
> time to a show she wanted to see.  I got lucky by finding it would
> work on the windows box.
> Thanks,
> Bob

Are you using btaudio?  You might need to make sure your audio sample 
rate for capture is 32000Hz.  Most bttv cards only support this sample 
rate.  If you're recording your audio at a sample rate that's higher 
than the actual, your entire playback will be sped up.  So if you're 
recording with a 48000Hz sample rate, your playback (in Myth) will 
likely be 48/32 = 1.5 times faster than it should.  Remember that's 
"sample rate", not "bit rate".

You might also play around with the "use video as timebase" option in 
Setup->TV->Playback, but if you're recording at the wrong sample rate 
then that will also probably give you weird results (perhaps slow or 
stuttering audio?).


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