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• Cant find file or directory

  25 juillet 2019, par Mister from Belarus

  Suprocess cant find file or directory from python script

  I`ve tried to convert mp3 to wav with subprocess and it works with cmd, when i write ffmpeg -i file.mp3 file.wav, but indetical code on python cant find my files. ffmpeg version N-94387-g923d5c489f.

  subprocess.call([’ffmpeg’, ’-i’, ’file.mp3’,
  ’file.wav’], cwd=r’C :/Users/Lenovo/Desktop’)

  Users/Lenovo/PycharmProjects/coloon/main.py
  Traceback (most recent call last) :
  File "C :/Users/Lenovo/PycharmProjects/coloon/main.py", line 4, in
  ’file.wav’], cwd=r’C :/Users/Lenovo/Desktop’)
  File "C :\Users\Lenovo\AppData\Local\Programs\Python\Python36\lib\subprocess.py", line 267, in call
  with Popen(*popenargs, **kwargs) as p :
  File "C :\Users\Lenovo\AppData\Local\Programs\Python\Python36\lib\subprocess.py", line 707, in init
  restore_signals, start_new_session)
  File "C :\Users\Lenovo\AppData\Local\Programs\Python\Python36\lib\subprocess.py", line 990, in _execute_child
  startupinfo)
  FileNotFoundError : [WinError 2] Не удается найти указанный файл

  I`ve also tried to use this

  subprocess.call(['ffmpeg', '-i', r'D:/file.mp3',
  
                   r'D:/file.wav'])

  but result is the same.

• How to find a "safe" point for -SS using FFMPEG to avoid breaking A/V sync ?

  16 juillet 2019, par user3144514

  I need to find a way to cut video using -SS without breaking the audio/video sync.

  Once in a while it works perfectly fine, but most of the time the audio falls slightly out of synch. Clearly there is something akin to a keyframe for audio, but I do not know how to find them.

  The problem happens when using -SS in conjunction with Any specification for a codec, including -c copy.

  For my purposes, I can’t lose quality so those are necessary.

  ffmpeg -i src.mp4 -ss 1:00 -t 30 -c copy result.mp4

  tends to break the sync.

  ffmpeg -i src.mpr -ss 1:00 -t 30 result.mp4

  produces matching a/v but with significant quality loss from using the default compressions.

  I need a way to find the times at which a cut will result in matching a/v.

• How to find the Quantified transformed coefficients in encoder x264 and in decoder libavcodec ?

  8 juillet 2019, par Quentin CHARRIER

  I’m a student in computer science and I am working on h264 encoder and decoder.

  I decided to use x264 and libavcodec and I downloaded code of these open libraries. Then, I searched for a month on how to do it. I think the quantified transformed coefficients are in h->dct.luma8x8 and h->dct.luma4x4 but they are no luma16x16 so I’m disappointed.

  Now, I suppose that Intra 16x16 macroblock have their coefficients in luma4x4 or luma8x8 but I’m not sure. Is there someone who knows about it and could give answers ?

  Furthermore, I have to find the same coefficients in decoder and I thought that they are in sl->mb but the coefficients in sl->mb are strange (there are a lot of 0s and values > 100 contrary to the encoder where values are close to 1-10..) I’m lost so I hope that someone have some advice to help me to continue my project.

  EDIT :

  I think the coefficients when the macroblock is encoded in 16x16IntraPrediction are in luma4x4. I always need help to understand how the decoder works.

  EDIT :

  I think the coefficients which are in sl->mb are always dequantized, maybe there is a variable who have the correct coefficient in decode_cabac_residual_internal but I didn’t find it..