| | 76 | === Specifying input framerate === |
| | 77 | |
| | 78 | You can set framerate like {{{ffmpeg -f dshow -framerate 7.5 -i video=XXX}}}. This instructs the device itself to send you frames at 7.5 fps [if it can]. |
| | 79 | |
| | 80 | Be careful *not* to specify framerate with the "-r" parameter, like this {{{ffmpeg -f dshow -r 7.5 -i video=XXX}}}. This actually specifies that the devices incoming PTS timestamps be *ignored* and replaced as if the device were running at 7.5 fps [so it runs at default fps, but its timestamps are treated as if 7.t fps]. This can cause the recording to have "video faster than audio" or, under high cpu load (if video frames are dropped) it will cause the video to fall "behind" the audio [after the recording is done, audio continues on--and highly out of sync]. |
| | 81 | |
| | 82 | If you want say 10 fps, and you device only supports 7.5 and 15 fps, then run it at fps then "downsample" to 10 fps. There are a few ways to do this--you could specify your output to be 10 fps, like this: {{{ffmpeg -f dshow -framerate 15 -i video=XXX -r 10 output.mp4}}} or insert a filter to do the same thing for you: {{{ffmpeg -f dshow -framerate 15 -vf fps=fps=15 output.mp4}}}. |
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| | 84 | |
