Strange frame rates in camera-phone video

[ipanema]

I have a smart phone which seems to record video at 29.692 fps. It seems to be quite a common rate according to a Google search. But surely it should be 29.94. Is there a reason why 29.692 is used?

Also, how do we make the frame rate 29.94 which is required for DVD compliance? If the frame rate is forced to 29.94 the a/v sync is eventually going to drift.

[Asmodian]

I have no idea why it might happen but you can force it for the audio too, you shouldn't notice the 0.8% speedup.

ResampleAudio (http://avisynth.org/mediawiki/ResampleAudio)(47602.4048096)
AssumeSampleRate(48000)

[Ghitulescu]

Since a smartphone is not a videocamcorder, the frame rate and other parameters are generally "relaxed" - it might be the case where several frames have been dropped and the fps is changed (as a median). Since there's a ~0.9% deviance, I exclude a priori that the internal quartz clock is that off, but no one knows ;)

And it's 29.97 not 29.94, which still is not DVD conform as smartphones are progressive while the DVDs are interlaced (59.94i).

[ipanema]

Thanks for the replies. As you say smartphones (and other phones) do seem to have more relaxed frame rates.

I also found a thread where iphone users were complaining that the frame rate varied between 24 and 30 depending on the ambient light conditions, and that this made it difficult to make DVDs etc. They didn't mention whether the frame rate stayed fixed for a whole clip, or if the frame rate actually changed while a clip was being recorded which would have been even worse.

[bigotti5]

And it's 29.97 not 29.94, which still is not DVD conform as smartphones are progressive while the DVDs are interlaced (59.94i).

DVD Video is neither interlaced nor progressive - just framerate matters (25 or 29.97)