[FFmpeg-user] Image extraction broken with ffmpeg, but not with mencoder. How can I fix this?

[James Board]

>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?