amindfv--- via ffmpeg-user (12021-08-20): > I then tested the output of running commands like this, only changing the > value for $STARTTIME : > > export STARTTIME=0.33 ; ffmpeg -r 24 -i color-frames.mp4 -r 24 -ss > $STARTTIME "test-$STARTTIME.mp4"
There are several flaws in problem report: - You did not post the full output. We need the full output to spot some usual missteps. - You do not need export since you are using the variable directly. - By adding -r on your input, your force ffmpeg to re-synthesize the timestamps. This is wrong in general. In this particular case, it changes the precision of the timestamps: your input file has a 1/12288 time base, with -r 24 it becomes 1/24. - By adding -r on your output and by using a format like MP4 that only supports constant frame rate, you are forcing ffmpeg to duplicate or drop frames to a certain rate. If you want to examine the output carefully, either use a format that supports arbitrary timestamps or do not use a format at all and write to individual images with "-vsync passthrough". It is possible you have unearthed an off-by-one bug somewhere. But in general, the logic should be: - The timestamps you write are rounded to the nearest integer multiple of the time base. - The frames you get in the filter line are exactly the interval you requested. That means if the time base is more precise than the frame rate you can get frames with half the duration. What happens after the filter chain, on the other hand, is subject to more complex heuristics. I strongly suggest you try to work as much as possible only with filters. > On Wed, Aug 18, 2021 at 09:26:03PM -0600, amindfv--- via ffmpeg-user wrote: Top-posting is forbidden on this mailing-list. Do not do it again if you want help. Look it up if you do not know what it means. Regards, -- Nicolas George
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