ffmpeg command help sheet

ffmpeg-cmds

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# basic video conversion
ffmpeg -i input.flv output.webm


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# get frame count (realy simple : show in stdout)
ffmpeg -i "a.flv" -f null /dev/null


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# add green screen to test_videos : bg.png is a green image
# 
# -loop 1       => loop over the bg.png to mimic a video
# -i bg.png     => the background source image, in our case a green image
# -r xx         => the frame rate, xx number of frame per seconds
# -vframes xx   => the number of frame of the video, the input video being a fake looped image, we have to speciafy the number of total frames
# -vf           => the filter that fake the actual video bein an "logo" overlay above our fake png video
# -s            => the size of the video output
# -y            => the name.ext of the ouput video

ffmpeg -loop 1 -i bg.png -r 30 -vframes 31 -vf "movie=a.flv [logo]; [in][logo] overlay=0:0 [out]" -s 154x132 -y green.mp4


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# add the alpha chanel in a splited video below normal video

ffmpeg -i input.flv -vf "split [a], pad=iw:2*ih [b], [a] alphaextract, [b] overlay=0:h" -y output.mp4