[FFmpeg-user] Frame rate discrepancy

[Dave Blanchard]

Hi all, I'm pulling video off a capture card for a surveillance application. I use the -t option to ffmpeg to record a 6 hour segment of video, then stop and start another segment. The problem is the timestamp of the next video file is advanced about 21 seconds from where it's supposed to be. For example if the first video were timestamped 6:00:00 UTC, the next one will start at 12:00:24 instead of 12:00:03 where it should be, taking into account time needed to start and stop the recording. It's like there is really 6:00:21 of video being pulled off the card, but it's being output at a (very) slightly higher framerate, resulting in a 6:00:00 file. This seems to be due to NTSC 30000/1001 framerate vs. straight 30 fps discrepancy. I haven't been able to figure out exactly why this is happening. Can anyone give me a tip on what's going on here and how to solve it? Thanks in advance.

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Dave Blanchard <dave at killthe.net>