[FFmpeg-user] Image extraction broken with ffmpeg, but not with mencoder. How can I fix this?
jpboard2 at yahoo.com
Tue Sep 3 16:41:53 CEST 2013
>In the future, maybe you will remember you should never work with frame
>numbers but always with timestamps.
1: I'm using ffmpeg to separate a video file into a sequence of frames. In
doing so, ffmpeg generates extra frames. This is the problem. Whether or
not I used frame numbers, or timestamps, this would still be the case.
2: Ultimately I must use frame numbers because I need to know which
frames (which are stored as distinct files) to include and which not to include.
3: Timestamps are floating-point numbers, and floating-point numbers are not exact.
Frame numbers are integers and integers are exact. I asked previously for a
formula to map timestamps to frame numbers and didn't get an answer. Here's
the issue: If I try to use a time stamp that falls midway between two frames, which frame will ffmpeg
select? What if I try to use a timestamp that is .000001 less than the timestamp of
the frame I want? Will ffmpeg round to the nearest frame, or round down to the previous
frame, or round up to the next frame, or does ffmpeg even do anything consistent?
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