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• Complex audio volume changes with ffmpeg

  29 juin 2016, par coco

  Using ffmpeg, how much control can we have over the audio levels ? For example, I would like to map an "M" shape over the program’s timeline :

  t0 - t1 : fade in from 0 to 1
  
  t1 - t2 : play at full volume
  
  t2 - t3 : fade out to 25%
  
  t3 - t4 : play at 25% volume
  
  t4 - t5 : fade in (from 25%) to full volume
  
  t5 - t6 : play at full volume
  
  t6 - t7 : fade out from 1 to 0

  Can this be done ? The combinations I’ve tried (of afade and volume, and using timeline editing) have not been successful so far.

  Here is something that is close :

  ina="infile.caf"
  
  out="outfile.mp3"
  
  
  
  time ffmpeg -i $ina -af \
  
  "afade=enable='between(t,0,3)':t=in:ss=0:d=3, \
  
  afade=enable='between(t,7,8)':t=out:st=7:d=1, \
  
  volume=enable='between(t,8,12)':volume=.25:eval=frame, \
  
  afade=enable='between(t,12,13)':t=in:st=12:d=1, \
  
  afade=enable='between(t,15,18)':t=out:st=15:d=3" \
  
  $out

  .. but at the two middle points (the point where it fades out to 25%, and the point where it fades back in to full volume) there are glitches - audible sound clicks.

• FFmpeg - filter-chaining and mapping output

  15 décembre 2022, par o_ren

  In FFmpeg, is it possible to map an output from the middle of a filter chain ?

  


  For example, in this command :

  


  ffmpeg -f lavfi -i smptehdbars=rate=25:size=1920x1080 -filter_complex "[0:v]drawtext=text=text1:x=100/2:y=100:fontsize=50[txt1];[txt1]drawtext=text=text2:x=200/2:y=200:fontsize=50[txt2];[txt2]drawtext=text=text3:x=300/2:y=300:fontsize=50[txt3];[txt3]drawtext=text=text4:x=400/2:y=400:fontsize=50[txt4]" -map "[txt4]" -t 10 -y ~/Desktop/mapping.mp4


  


  This works : -map "[txt4]".
When trying -map "[txt3]" (or txt2, or txt1) I get "

  


  


  Output with label 'txt3' does not exist in any defined filter graph,
or was already used elsewhere."

  


  


  Thanks

  


• avcodec/mpegaudiodec_template : Check CRCs for layer1 and layer2

  3 août 2020, par Michael Niedermayer

  avcodec/mpegaudiodec_template : Check CRCs for layer1 and layer2
  This differs from the MPEG specification as the actual real world
  
  files do compute their CRC over variable areas and not the fixed
  
  ones listed in the specification. This is also the reason for
  
  the complexity of this code and the need to perform the CRC
  
  check for layer2 in the middle of layer2 decoding.
  Reviewed-by : Lynne <dev@lynne.ee>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/mpegaudiodec_template.c