Thread: ffmpeg: expression evaluator

hi,

i'm using ffmpeg produce video series of still images this:

ffmpeg -f image2 -r 25 -i img%03d.jpg -vcodec h263p -r 25 vid.avi

first '-r 25' determines how many images progressed create 1 second of video, second '-r 25' framerate of video (vid.avi). if want succession of images faster (e.g. double speed) keeping framerate @ 25 fps use e.g.:

ffmpeg -f image2 -r 50 -i img%03d.jpg -vcodec h263p -r 25 vid.avi

works fine, far. i'd now, change number of progressed images per second of video continuously from, 50 25, within video, i.e. video @ fast speed (50 images per second) in begining , @ normal speed (25 images per second) in end of video. symbolically, want like

ffmpeg -f image2 -r 50:25 -i img%03d.jpg -vcodec h263p -r 25 vid.avi

idea is, solve expression evaluation of ffmpeg , use current frame variable determine integer between 50 , 25. have trouble understand how can access number of current frame , write proper function instead of 50:25 above, ffmpeg understands. not find example how use expression evaluation of ffmpeg, maybe 1 of guys have experience , me started? in advance!

Forum The Ubuntu Forum Community Ubuntu Official Flavours Support Multimedia Software [ubuntu] ffmpeg: expression evaluator

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