[FFmpeg-user] Frame rate and movies from images

thljcl jiachielee at live.com
Mon Jul 22 01:30:32 CEST 2013

You made an error for not recognizing the difference between -r as an input
option or output option. If your source is a series of image sequence,
ffmpeg will assume the frame rate of 25 FPS if none is specified as the
input option; if your source is a video file, the frame rate of the source
will be regarded as input option if none is specified. Just type -r "6"
before -i should serve your purpose, if I understand you correctly. -r
before -i will force the frame rate on the source while ignoring the frame
rate of the source, which will result in slowing down or speeding up of the
playback of the video. -r after -i is the frame rate for output video, which
if the frame rate is high enough, will preserve the playback speed or the
length by adding or dropping frames. If the source is of variable frame
rate, specifying a different frame rate as the output option may cause the
output video out of sync with audio, mainly due to changing frame rate of
the source itself; even though the input video is perfectly in sync with
audio. Encoding a video into a series of image sequences and specifying a
frame rate as an output option can force the frame rate to be constant while
preserving the original length.

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