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• Compressing mp3s that contain mostly silence

  2 mars 2019, par cjmaria

  I am looking for the optimal way to compress a large mp3 that contains >80% silence. It seems like mp3s consume nearly the same amount of space for a given duration independent of the content of the file. Are there any other compression formats that would do a better job of reducing the file size without significantly affecting quality of the non-silent parts ?

• Concatenate mp4 files

  17 juillet 2020, par jap101

  I want to concatenate around 15 45 second clips together end on end. These clips can be of different resolution (most are 1080 or 720) but are all mp4 files.

  


  i have tried both

  


  concatenate_videoclips(clips,method='compose')
concatenate_videoclips(clips,method='chain')


  


  from moviepy but neither of these are good for me since 'compose' relies on all the files being the same resolution which they are not and chain takes too long and sometimes causes errors.

  


  i have also tried using ffmpeg with :

  


  ffmpeg -i clip1.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts


  


  for each clip and then concatenating with :

  


  ffmpeg -i "concat:intermediate1.ts|intermediate2.ts|...|intermediate15.ts" -c copy -bsf:a aac_adtstoasc output.mp4


  


  but this method seemed to cause a audio problem i believe due to the lossless compression when changing file type. There are these strange audio pauses periodically throughout the video.

  


  i have also tried ffmpeg

  


  ffmpeg -f concat -safe 0 -i clipsfile.txt -c copy output.mp4


  


  where the clipsfile.txt looks like

  


  file clip1.mp4
file clip2.mp4
...
file clip15.mp4


  


  when i run this it works but i have an audio error where someclips (often comes in pairs) where one clip is silent and then the next clip plays the audio from the previous clip but of the first clip is shorter the audio will go back to the second clips audio at the correct time so it seems to me like the audio is overlaps and causes it to be silent and then when the overlap stops it goes back to normal.

  


  Any suggestions to fix any of these, extra information or recommendations of other things to do are much appreciated thanks.

  


• is there a single command to process different audio layouts ? [closed]

  10 août 2023, par Omer Weiss

  I want to use a single ffmpeg command that will output a single stereo audio track.
My problem is that I want to use a single command for 2 possible layouts on the input :
1 : a single stereo track
2 : two mono tracks.

  


  to put in filtergraph terms, the output should have option #1's [0:a:0:0] or option #2's [0:a:0] as Left and option #1's [0:a:0:1] or option #2's [0:a:1] as Right.

  


  Explicit reference results in runtime error (Invalid stream specifier).

  


  this command does the right thing on the single stereo input (op#1) but results in silent Right on 2 mono tracks op#2) :

  


  ffmpeg -i $1 -filter_complex "[0:a]pan=stereo|c0=c0|c1=c1[out]" -map 0:v -map "[out]" -c:v copy -c:a aac -strict experimental -b:a 192k -ac 2 -ar 44100 -acodec aac -ab 192k "merged_$1.mp4"

  


  this command does the right thing on the single stereo input (op#1) but results in silent Right on 2 mono tracks op#2) :

  


  ffmpeg -i $1 -filter_complex "[0:a]pan=stereo|c0=c0|c1=c1[out]" -map 0:v -map "[out]" -c:v copy -c:a aac -strict experimental -b:a 192k -ac 2 -ar 44100 -acodec aac -ab 192k "merged_$1.mp4"

  


  I am looking for ways to suppress 'invalid stream specifier'.