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• Why does ffmpeg command work in terminal but not subprocess.call

  4 août, par Brian

  I reviewed the "similar questions", but those seem to refer to using the full path for ffmpeg to ensure using the same version, which I am already doing so posting my question.

  


  I am using a Mac runnning Sequoia 15.5, python 3, and ffmpeg 4.2.1.

  


  I'm trying to write a script that can convert flac to mp3 320k.

  


  If I use the following command in terminal everything works as intended :

  


  /usr/local/bin/ffmpeg -i "/Volumes/MainData/Media/Media Server/_Stage/03 - People Like Us - Aaron Tippin.flac" -b:a 320k -map_metadata 0 -id3v2_version 3 "/Volumes/MainData/Media/Media Server/_Stage/03 - People Like Us - Aaron Tippin.mp3"


  


  But when trying to do the same thing with subprocess.call with the following :

  


  command = ['/usr/local/bin/ffmpeg', '-i', '/Volumes/MainData/Media/Media Server/_Stage/03 - People Like Us - Aaron Tippin.flac', '-b:a 320k', '-map_metadata 0', '-id3v2_version 3', '/Volumes/MainData/Media/Media Server/_Stage/03 - People Like Us - Aaron Tippin.mp3']
p = subprocess.call(command)


  


  I get this as a result :

  


  Unrecognized option 'id3v2_version 3'.
Error splitting the argument list: Option not found


  


  If I remove the '-id3v2_version 3', then the subprocess.call results in the following error :

  


  [mp3 @ 0x7fae2c008200] Invalid stream specifier: a 320k.


  


  Why does Terminal understand but subprocess.call doesn't when I've verified I'm using the same version of ffmpeg ?

  


• sending variables to subprocess call with spaces - python 2.7

  24 novembre 2015, par Tandy Freeman

  I want to add ffmpeg options to a variable and later use it in a subprocess call. If the variable contains one word, all is well, but if it contains more than one, I get errors. I am working on a larger script and I will need to have extra options such as this for certain codecs. How can I get this working ?

  The following works perfectly for me :

  import subprocess
  
  import sys
  
  
  
  video_codec = 'libx264'
  
  output = sys.argv[1] + '.mkv'
  
  subprocess.call(['ffmpeg',
  
              '-i',sys.argv[1], 
  
              '-c:v',video_codec,
  
              '-c:a','copy',         
  
              output])    

  Once I introduce new options/spaces to video_options as such :

  video_codec = "'libx264', '-pix_fmt', 'yuv420p'"

  I get an ffmpeg error :

  Unknown encoder ''libx264', '-pix_fmt', 'yuv420p''

  If I remove the double quotes and just use
  video_codec = ’libx264’, ’-pix_fmt’, ’yuv420p’

  I get a python error :

  Traceback (most recent call last):
 File "testo.py", line 10, in <module>
   output])<br />
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 524, in call
   return Popen(*popenargs, **kwargs).wait()
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 711, in __init__
   errread, errwrite)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 1308, in _execute_child
   raise child_exception
TypeError: execv() arg 2 must contain only strings
</module>

• I called av_probe_input_format3(), now I want to call avcodec_find_decoder(), how do I convert the format in a codec ?

  27 janvier 2021, par Alexis Wilke

  So... I'm dealing with a system that has input data coming in buffers (i.e. NOT a file). I want to determine which decoder to create to decompress an audio stream (MP3, WAV, OGG, ...) So obviously I do not know the input format.

  


  I found out that I could determine the format using the av_probe_input_format[23]() functions. That part works great, I get a format pointer that matches the files that I use as input.

  


  AVInputFormat * format(av_probe_input_format3(&pd, true, &score));


  


  I can print the format->name and format->long_name and these are the correct type (so the detection is working as expected).

  


  Now, I'm trying to understand how to convert that AVInputFormat * into a AVCodec * so I can call avcodec_alloc_context3(codec) to create the actual audio decoder.

  


  I found a couple of functions, which I used like so :

  


  AVCodecID const codec_id(av_codec_get_id(format->codec_tag, format->raw_codec_id));
AVCodec * codec(avcodec_find_decoder(codec_id));


  


  Problem 1. the raw_codec_id field is marked as "private" (should not access/use anywhere in your client's code).

  


  Problem 2. the first function always returns AV_CODEC_ID_NONE (0) so of course the second call fails each time.

  


  Am I doing something wrong ? Is there is way to instead create a generic decode that will automatically detect the type of audio I have as input ? (that is, would that be the only way to make that work ?)