Using ffmpeg to change framerate

Question

I am trying to convert a video clip  MP4  yuv420p  from 30 fps to 24 fps  The number of frames is correct so my output should change from 20 minutes at 30fps to 25 minutes at 24fps  Everything else should remain the same   Try as I might everything I try with ffmpeg converts the frame rate but changes the number of frames to keep the same duration or changes the duration without altering the framerate   So I have been typically trying things like   ffmpeg -y -r 30 -i seeing noaudio mp4 -r 24 seeing mp4    I m doing this on windows but normally would be on linux   That converts the framerate but drops frames so the total duration is unaltered   Or I have tried   ffmpeg -y -i seeing noaudio mp4 -filter v  setpts 1 25 PTS  seeing mp4   Which changes the duration but not the framerate   Surely I should be able to do this with a single ffmpeg command without having to reencode or even as some people suggested going back to the original raw frames   Help please

User · Answer

In general  to set a video s FPS to 24  almost always you can do  With Audio and without re-encoding    Extract video stream ffmpeg -y -i input video mp4 -c copy -f h264 output raw bitstream h264   Extract audio stream ffmpeg -y -i input video mp4 -vn -acodec copy output audio aac   Remux with new FPS  ffmpeg -y -r 24 -i output raw bitstream h264 -i output-audio aac -c copy output mp4  If you want to find the video format  H264 in this case   you can use FFprobe  like this ffprobe -loglevel error -select streams v -show entries stream codec name -of default nw 1 nk 1 input video mp4  which will output   h264  Read more in How can I analyze file and detect if the file is in H 264 video format   With re-encoding  ffmpeg -y -i input video mp4 -vf -r 24 output mp4

User · Answer

To the best of my knowledge you can t do this with ffmpeg without re-encoding  I had a 24fps file I wanted at 25fps to match some other material I was working with  I used the command ffmpeg -i inputfile -r 25 outputfile which worked perfectly with a webm matroska input and resulted in an h264  matroska output utilizing encoder  Lavc56 60 100  You can accomplish the same thing at 6fps but as you noted the duration will not change  which in most cases is a good thing as otherwise you will lose audio sync   If this doesn t fit your requirements I suggest that you try this answer although my experience has been that it still re-encodes the output file   For the best frame accuracy you are still better off decoding to raw streams as previously suggested  I use a script for this as reproduced below      bin bash  This script will decompress all files in the current directory  video to huffyuv and audio to PCM  unsigned 8-bit and place the output  in an avi container to ease frame accurate editing  for f in   do ffmpeg -i   f  -c v huffyuv -c a pcm u8   f  avi done   Clearly this script expects all files in the current directory to be media files but can easily be changed to restrict processing to a specific extension of your choosing  Be aware that your file size will increase by a rather large factor when you decompress into raw streams

User · Answer

You may consider using fps filter  It won t change the video playback speed   ffmpeg -i  lt input gt  -filter v fps fps 30  lt output gt    Worked nice for reducing fps from 59 6 to 30

User · Answer

With re-encoding   ffmpeg -y -i seeing noaudio mp4 -vf  setpts 1 25 PTS  -r 24 seeing mp4   Without re-encoding   First step - extract video to raw bitstream  ffmpeg -y -i seeing noaudio mp4 -c copy -f h264 seeing noaudio h264   Remux with new framerate  ffmpeg -y -r 24 -i seeing noaudio h264 -c copy seeing mp4

User · Answer

Simply specify the desired framerate in  -r   option before the input file   ffmpeg -y -r 24 -i seeing noaudio mp4 seeing mp4   Options affect the next file AFTER them   -r  before an input file forces to reinterpret its header as if the video was encoded at the given framerate  No recompression is necessary  There was a small utility avifrate exe to patch avi file headers directly to change the framerate  ffmpeg command above essentially does the same  but has to copy the entire file

User · Answer

You can use this command and the video duration is still unaltered   ffmpeg -i input mp4 -r 24 output mp4

[ffmpeg] Using ffmpeg to change framerate

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