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• setting a correct ffmpeg GOP (group of pictures) [closed]

  9 mai 2013, par Robert Cantarutti

  I'm using ffmpeg to ser the GOP (Group of pictures) with mpeg4.
  I had success to set a GOP of :
   12,2 (12 frames between two I frames, and 2 frames between each P frames)
   15,2
   18,2
   30,2
  And I had not success in this cases :
   8,2
   4,2

  1- Example to set a GOP of 12,2 :
  ffmpeg -s cif -r 30 -i video.yuv -vcodec mpeg4 -g 12 -bf 2 -sameq video.m4v

  2-Example to set a GOP of 8,2 :
  ffmpeg -s cif -r 30 -i video.yuv -vcodec mpeg4 -g 8 -bf 2 -sameq video.m4v

  1. The result of (1) - ok :

  $ head trace
  ...
  11 H 20313 14 0.43
  12 B 10752 8 0.43
  13 B 10718 8 0.43
  14 P 12643 9 0.529
  15 B 11338 8 0.529
  16 B 11136 8 0.529
  17 P 12999 9 0.634
  18 B 10666 8 0.634
  19 B 11000 8 0.634
  20 P 12530 9 0.727
  21 B 10345 8 0.727
  22 B 10887 8 0.727
  23 H 20300 14 0.825
  24 B 11258 8 0.825
  25 B 10759 8 0.826
  26 P 12482 9 0.925
  27 B 10871 8 0.925
  28 B 11249 8 0.925
  29 P 13229 10 1.024
  30 B 11003 8 1.024
  31 B 10904 8 1.024
  32 P 12788 9 1.123
  33 B 11063 8 1.123
  34 B 11365 8 1.123
  35 H 20253 14 1.234

  1. The result of (2) - nok :

  ...
  8 H 19824 14 0.33
  9 B 11238 8 0.331
  10 B 11566 8 0.331
  11 P 13314 10 0.929
  12 B 11117 8 0.929
  13 B 11152 8 0.929
  14 H 19683 14 0.929
  15 B 11002 8 0.93
  16 B 10827 8 0.93
  17 P 13240 10 0.93
  18 B 11060 8 0.93
  19 B 11220 8 0.93
  20 H 19942 14 0.93
  21 B 10353 8 2.283
  22 B 10897 8 2.283
  23 P 13386 10 2.283
  24 B 11433 8 2.283
  25 B 10945 8 2.283
  26 H 19623 14 2.284
  27 B 10630 8 2.284
  28 B 11247 8 2.284
  29 P 13430 10 2.284
  30 B 11294 8 2.284
  31 B 10954 8 2.284
  32 H 19654 14 2.351
  33 B 10989 8 2.352
  34 B 11127 8 2.352
  35 P 13630 10 2.352
  36 B 11121 8 2.352
  37 B 11640 8 2.352
  38 H 19691 14 2.352
  39 B 11426 8 2.353
  40 B 11294 8 2.353
  41 P 12675 9 2.353
  42 B 11705 9 2.353
  43 B 11333 8 2.399
  44 H 19659 14 2.399

  Note : "I" frames is same as "H" above.

  First :
  1-Itś possible to have a GOP 8,2 and 4,2 ?
  2-How they are ? Ex. : I,B,B,P,B,B,P,B,I ? I,B,B,P,B,I ?

• How to increase de volume of an interval of an mp3 file with ffmpeg ?

  30 avril 2017, par user2128078

  I’d like to increase de volume of an interval of and mp3 file, i.e. from 20s to 30s increase in 15%. I’m using ffmpeg.

  Thank you so much for your help !

  Regards,

  Raul.

• How to read realtime microphone audio volume in python and ffmpeg or similar

  20 octobre 2016, par Ryan Martin

  I’m trying to read, in near-realtime, the volume coming from the audio of a USB microphone in Python.

  I have the pieces, but can’t figure out how to put it together.

  If I already have a .wav file, I can pretty simply read it using wavefile :

  from wavefile import WaveReader
  
  
  
  with WaveReader("/Users/rmartin/audio.wav") as r:
  
      for data in r.read_iter(size=512):
  
          left_channel = data[0]
  
          volume = np.linalg.norm(left_channel)
  
          print volume

  This works great, but I want to process the audio from the microphone in real-time, not from a file.

  So my thought was to use something like ffmpeg to PIPE the real-time output into WaveReader, but my Byte knowledge is somewhat lacking.

  import subprocess
  
  import numpy as np
  
  
  
  command = ["/usr/local/bin/ffmpeg",
  
              '-f', 'avfoundation',
  
              '-i', ':2',
  
              '-t', '5',
  
              '-ar', '11025',
  
              '-ac', '1',
  
              '-acodec','aac', '-']
  
  
  
  pipe = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=10**8)
  
  stdout_data = pipe.stdout.read()
  
  audio_array = np.fromstring(stdout_data, dtype="int16")
  
  
  
  print audio_array

  That looks pretty, but it doesn’t do much. It fails with a [NULL @ 0x7ff640016600] Unable to find a suitable output format for ’pipe :’ error.

  I assume this is a fairly simple thing to do given that I only need to check the audio for volume levels.

  Anyone know how to accomplish this simply ? FFMPEG isn’t a requirement, but it does need to work on OSX & Linux.