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• Using decibel values, how to detect if the user is talking or silent ?

  26 juin 2021, par Nadir Abbas

  I have used FFMPEG to extract decibel (or rms ? I am not familiar with the units) values of the audio volume from an mp4. I have 20 samples per frame.

  


  

  


  How can I use these values (which are negative in almost all frames), to determine if the frame is silent or has audio (music, speech, etc) ?

  


• How to add audio to specific time [ffmpeg]

  20 mai 2019, par EJL

  So far, I’ve manage to add audio to the video in ffmpeg but it is playing all along. The enable=’between(t,start,end)’ option is not working

  I have tried googling for possible answers but my approach is different. I wanted to enable/disable the audio repeatedly in the video.

  SO far I have this code :

  ffmpeg -y -i cut.mp4 -i typing.mp3 -filter_complex "[0:v]drawtext=enable='between(t,0,3)':fontfile=fonts/RobotoBoldCondensed.ttf:text='Finding Nemo...':fontcolor=white:fontsize=24:x=50:y=h-h/5+20[v0]; [1:a]volume=enable='between(t,0,3)'[a3]" -vcodec libx264 -c:a libfdk_aac -map "[v0]" -map "[a3]" -preset ultrafast -async 1  output.mp4

• aacdec : move from scalefactor ranged arrays to flat arrays

  14 mai 2024, par Lynne

  aacdec : move from scalefactor ranged arrays to flat arrays
  AAC uses an unconventional system to send scalefactors
  
  (the volume+quantization value for each band).
  
  Each window is split into either 1 or 8 blocks (long vs short),
  
  and transformed separately from one another, with the coefficients
  
  for each being also completely independent. The scalefactors
  
  slightly increase from 64 (long) to 128 (short) to accomodate
  
  better per-block-per-band volume for each window.
  To reduce overhead, the codec signals scalefactor sizes in an obtuse way,
  
  where each group's scalefactor types are sent via a variable length decoding,
  
  with a range.
  
  But our decoder was written in a way where those ranges were carried through
  
  the entire decoder, and to actually read them you had to use the range.
  Instead of having a dedicated array with a range for each scalefactor,
  
  just let the decoder directly index each scalefactor.
  This also switches the form of quantized scalefactors to the format
  
  the spec uses, where for intensity stereo and regular, scalefactors
  
  are stored in a scalefactor - 100 form, rather than as-is.
  USAC gets rid of the complex scalefactor handling. This commit permits
  
  for code sharing between both.
  

  • [DH] libavcodec/aac/aacdec.c
  • [DH] libavcodec/aac/aacdec.h
  • [DH] libavcodec/aac/aacdec_dsp_template.c