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• FFMpeg : scale down videos with maximum width and height while maintaining aspect ratio

  20 février 2021, par R3D34THR4Y

  In my program the user can input any video file he wants and have it transcoded ready for social media no matter its dimensions and aspect ratio.
The "export profiles" have many variables but the important ones here are maxheight and maxwidth.

  


  The FFMpeg filters must output a video that follows the following rules :

  


  

  • If the video is vertical, permutate the maxheight and maxwidth values (social media considers both 1280x720 and 720x1280 as "720P")

  


  • The video must not have a height superior to maxheight or a width superior to maxwidth.

  


  • The original video and exported video have the same aspect ratio and no distortion occurs.

  


  • No padding or cropping should occur.

  


  • The video should not be scaled if it is already under those maximum dimensions (no upscaling).

  


  • The function must work even with odd input resolutions.

  


  


  I have tried finding a combination of filters that do that but I haven't been able so far, either the video gets distorted or it gets huge black bars if the aspect ratio isn't right, the solution may be simple but I'm a beginner on this library so I'm probably just missing an easy solution.

  


  My current solution :

  


  ffmpeg -i input.mp4 -vf [in] scale=1280:720:flags=lanczos:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1 [res]; [res] format=yuv420p [format] -c:v libx264 -c:a aac -movflags +faststart output.mp4


  


  Thanks for reading

  


• FFMpeg + OpenAL

  24 juillet 2013, par Dekowta

  I've been having a problem decoding different codecs into PCM 16 little-endian which is the supported format for OpenAL (I believe that is correct).

  I am using the windows pre-compiled libraries for FFMpeg (dont know if that effects anything).

  The code I have so far is here http://pastebin.com/T4wGL72a

  I have aiff and wav working (though with single channel OpenAL wants to have half the frequency and im not really sure why).

  The main problem is encoded audio files.

  mp3 files play sometimes (sometime get missing header) but end up stuttering with noise and are high pitched.

  ac3 files played the first preloaded buffers and then the frame would not have any more decoded data in the data array (did not check to see if the packet fetched encoded data or not).

  ogg files are the same as ac3

  m4a files would never finish the frame so I have no idea what happens when they do.

  wma files stutter and have a lot of noise but it is not high pitched like mp3 files

  I don't work with audio very often so its difficult for me to get my head round it and this is also the first time I've worked with FFMpeg.

  I'm sure there is something i'm doing very wrong I just need a hand on pointing out where it is.

  Thanks

  Chris.

• ffmpeg read from a file and apply filter_complex at once

  30 janvier 2020, par AlexZheda

  I am feeding fls.txt into ffmpeg -i and applying concat and a speedup.

  fls.txt

  file 'input1.mp4'
  
  file 'input2.mp4'
  
  file 'input3.mp4'

  The command in one go looks as follows :

  ffmpeg  -i fls.txt     \
  
  -filter_complex "[0:v][0:a][1:v][1:a][2:v][2:a] concat=n=3:v=1:a=1 [v][a];\
  
  [v]setpts=0.5*PTS[v1];[a]atempo=2,asetpts=N/SR/TB[a1]"     \
  
  -c:v h264_nvenc -map "[v1]" -map "[a1]"  x2.mp4

  The output is really weird and says something like a stream is not found. And it also looks like as if it’s trying to understand the fls.txt itself and not its content as the parameters.
  What am I doing wrong here and how can I correct it ?
  Also, it’s a simplified example and I cannot write per hand 3 input file paths. I need it to be read from a file. I’m on windows 10 if that matters.

  EDIT :
  From doing the suggested edits and expanding the -filter_complex I get an error below.

  ffmpeg -f concat -safe 0 -i fls.txt     \
  
  -filter_complex "[0:v]setpts=0.5*PTS[v1];[v1]setpts=0.5*PTS[v2];[0:a]atempo=2,asetpts=N/SR/TB[a1];[a1]atempo=2,asetpts=N/SR/TB[a2]"     \
  
  -c:v h264_nvenc -map "[v1]" -map "[a1]" x2.mp4 \
  
  -c:v h264_nvenc -map "[v2]" -map "[a2]" x4.mp4

  error :

  Output with label 'v1' does not exist in any defined filter graph, or was already used elsewhere.