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• FFMPEG Partial Audio Filter of Video File

  12 avril 2024, par Cole

  I am trying to apply an audio filter to a section of the audio track on a video file.

  


  Here are some details.
"video.mp4" is 1 minute and 36 seconds long. I want to lower the pitch of the first 30 seconds of the file. The video track does not need any change, so I can copy that and only transcode the audio. Note, I will have to do this same operation to other videos, with the pitch change at different times. This one is at the beginning, however.

  


  I have used this post for inspiration : https://superuser.com/questions/977743/ffmpeg-possible-to-apply-filter-to-only-part-of-a-video-file-while-transcoding

  


  I have tried the following :

  


  ffmpeg -i video.mp4 -filter_complex "[0:a]trim=start=0:duration=30,rubberband=pitch=0.5[a2];[0:a]trim=start=30[a3]" [a2][a3]concat[a] -map [a] -map [0:v] -c:v copy output.mp4


  


  The above combines the trim and rubberband into one action, but maybe that does not work (same error). In the below I separate them out.

  


  ffmpeg -i video.mp4 -filter_complex "[0:a]trim=start=0:duration=30[a1];[a1]rubberband=pitch=0.5[a2];[0:a]trim=start=30[a3]" [a2][a3]concat[a] -map [a] -map [0:v] -c:v copy output.mp4


  


  My thought process with the above is to take the audio track [0:a] and trim it to the portion I want to edit, now a1. Then apply the filter and make that a2. Lastly, take the other portion of the audio and save it as a3 (is this step even necessary ?). I concatenate the modified audio and unmodified audio (a2 and a3, respectively), then map the audio and video channels and output the final product.

  


  The error I receive is below.

  


  [Parsed_trim_0 @ 0x5623a0b03040] Media type mismatch between the 'Parsed_trim_0' filter output pad 0 (video) and the 'Parsed_rubberband_1' filter input pad 0 (audio)
[AVFilterGraph @ 0x5623a0ab6100] Cannot create the link trim:0 -> rubberband:0
Error initializing complex filters.
Invalid argument


  


  I think that this error is related to an audio/video track issue, but I don't know where to begin. Where am I going wrong ? What other suggestions do you have that I have not considered ?

  


  Edit : Thank you for pointing out the atrim ! That solved that particular issue. There were some other issues I had to figure out as well.

  


• libavfilter/vf_fps : Rewrite using activate callback

  22 février 2018, par Calvin Walton

  libavfilter/vf_fps : Rewrite using activate callback
  The old version of the filter had a problem where it would queue up
  
  all of the duplicate frames required to fill a timestamp gap in a
  
  single call to filter_frame. In problematic files - I've hit this in
  
  webcam streams with large gaps due to network issues - this will queue
  
  up a potentially huge number of frames. (I've seen it trigger the Linux
  
  OOM-killer on particularly large pts gaps.)
  This revised version of the filter using the activate callback will
  
  generate at most 1 frame each time it is called.
  

  • [DH] libavfilter/vf_fps.c

• opus_silk : fix typo causing overflow in silk_stabilize_lsf

  15 décembre 2015, par Andreas Cadhalpun

  opus_silk : fix typo causing overflow in silk_stabilize_lsf
  Due to this typo max_center can be too large, causing nlsf to be set to
  
  too large values, which in turn can cause nlsf[i - 1] + min_delta[i] to
  
  overflow to a negative value, which is not allowed for nlsf and can
  
  cause an out of bounds read in silk_lsf2lpc.
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
  

  • [DH] libavcodec/opus_silk.c