[mythtv] bttv recordings run fast

Daniel Thor Kristjansson danielk at cat.nyu.edu
Sat Mar 6 13:35:35 EST 2004

On Sat, 6 Mar 2004, Andrew Mahone wrote:
]On Sat, 06 Mar 2004 01:28:34 -0800, "Bruce Markey" <bjm at lvcm.com> said:
]Hm, I thought that MythTV was timestamping frames so that it would know
]"when" to play them back.  Even with that, dropping a random 10 of every
]30 frames will result in video that looks quite poor.

I believe the timestamp is only honored with some of the experimental
settings. Normally it just assumes the framerate it got when starting
to play the video is correct. For my frame dropping patch I created
separate "recording" and "playback" framerates, so that when I started
dropping frames I could lower the playback framerate, but still be able
to jump around the video correctly using the recording framerate.
Also, it seems avdecoder always drops every B frame if it's going to
drop frames, this can be a lot of frames. It would be better if you
could drop only whatever portion of the B frames you need to drop to
keep up, but then syncing would be even harder.

When I tried to use the video timebase I got a lot of stuttering in the
audio, as if the recorder audio samplerate was a little bit slower
than the audio playback samplerate. Perhaps this was due to the time it
takes to show the frame vs an assumption in the code that it is instant.
Or perhaps there is something wrong with the sample rate on my audio
card, I get similar problems if I play another sample at a different
sample rate using another program while myth is playing.

-- Daniel

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