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• Python extract wav from video file

  31 octobre 2015, par xolodec

  Related :

  How to extract audio from a video file using python ?

  Extract audio from video as wav

  How to rip the audio from a video ?

  My question is how could I extract wav audio track from video file, say video.avi ?
  I read many articles and everywhere people suggest to use (from Python) ffmpeg as a subprocess (because there are no reliable python bindings to ffmpeg - the only hope was PyFFmpeg but i found it is unmaintaned now). I don’t know if it is right solution and i am looking for good one.
  I looked to gstreamer and found it nice but unable to satisfy my needs — the only way I found to accomplish this from command line looks like

   gst-launch-0.10 playbin2 uri=file://`pwd`/ex.mp4  audio-sink='identity single-segment=true ! audioconvert ! audio/x-raw-int, endianness=(int)1234, signed=(boolean)true, width=(int)16, depth=(int)16, rate=(int)16000, channels=(int)1 ! wavenc !  filesink location=foo.wav’ 

  But it is not efficient because i need to wait ages while playing video and simultaneously writing to wav file.

  ffmpeg is much better :

  avconv  -i foo.mp4  -ab 160k -ac 1 -ar 16000 -vn ffaudio.wav

  But i am unable to launch it from python (not as a command line subprocess). Could you please point me out pros and cons of launching ffmpeg from python as a command line utility ? (I mean using python multiprocessing module or something similar).

  And second question.

  What is simple way to cut long wav file into pieces so that i don’t break any words ? i mean pieces of 10-20 sec length with start and end during the pause in sentences/words ?

  i know how to break them on arbitrary pieces :

  import wave
  
  
  
  
  
  win= wave.open('ffaudio.wav', 'rb')
  
  wout= wave.open('ffsegment.wav', 'wb')
  
  
  
  t0, t1= 2418, 2421 # cut audio between 2413, 2422 seconds
  
  s0, s1= int(t0*win.getframerate()), int(t1*win.getframerate())
  
  win.readframes(s0) # discard
  
  frames= win.readframes(s1-s0)
  
  
  
  wout.setparams(win.getparams())
  
  wout.writeframes(frames)
  
  
  
  win.close()
  
  wout.close()

• Why do .bss/.rodata symbols stay in binary after strip ?

  15 novembre 2014, par BlahGeek

  As far as I know, there’s only one kind of symbols in executable binary that is really needed, which is dynamic symbols. These symbols is used in relocation operation because they are dynamic linked. Static linked functions/variables, in the other hand, is not needed so can be stripped.

  However, when I was examining the stripped ffmpeg binary, this is what I got :

  >nm -D ffmpeg
  
  ...
  
                   U __vfprintf_chk
  
                   U __vsnprintf_chk
  
                   U write
  
  00000000018fa880 B x264_cabac_contexts
  
  0000000001052a40 R x264_cabac_range_lps
  
  0000000001052940 R x264_cabac_transition
  
  0000000001970580 B x264_cabac_transition_unary
  
  0000000001056820 R x264_last_coeff_flag_offset
  
  0000000001056860 R x264_significant_coeff_flag_offset
  
  0000000001056900 R x264_significant_coeff_flag_offset_8x8
  
                   U __xpg_strerror_r
  
                   U __xstat64
  
  ...

  I can verify that libx264 is static linked to ffmpeg :

  > ldd ffmpeg
  
  linux-vdso.so.1 =>  (0x00007fff26d61000)
  
  libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f7c707e7000)
  
  libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f7c704e1000)
  
  liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f7c702be000)
  
  libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x00007f7c700ae000)
  
  libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f7c6fe95000)
  
  libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f7c6fc76000)
  
  libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7c6f8b0000)
  
  /lib64/ld-linux-x86-64.so.2 (0x00007f7c70b0a000)
  
  libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f7c6f69a000)
  
  libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f7c6f495000)

  So, I don’t understand why symbols like x264_cabac_contexts is not stripped. (It’s defined in libx264/.../cabac.c) :

  uint8_t x264_cabac_contexts[4][QP_MAX_SPEC+1][1024];

  It bothered me for several hours and I’ve found nothing on google... Hope someone would explain this... Thanks in advance !

• Creating a recursive ffmpeg converter

  23 novembre 2014, par Joe Healey

  I’m trying to create a script of some sort that will convert any video files it detects within a folder (also scanning subfolders), to an .avi file of the same name, in the same place, then remove the original file. I’ve not really used cmd much for any programming/scripting so I’m stumbling over what I suspect is some pretty simple syntax issues.

  If anyone is familiar with encoding and ffmpeg, please point out whether the encoding options are wrong (I’m stumbling about in the dark at the moment).

  Using this thread, I’m working with something currently resembling :

  dir/b/s *.(mkv|mp4|m4v|wmv) >listing.txt  #Make a list of all the files with certain extensions, for reading.
  
  for /F "delims=;" %%F in (listing.txt) do ffmpeg.exe  -i "%%F" -c:v libx264 -preset slow -crf 20 -c:a libvo_aacenc -b:a 128k "%%~na.avi"
  
  #Then to delete original files
  
  for /F "delims=;" %%F in (listing.txt) do del %%F
  
  del listing.txt

  The first issue I have is that I’d like to be able to populate the list with all the common video types. I’m imagining cmd has some syntax similar to perl string matching e.g. A(B|C) would match AB and AC that I could mimic for matching any video file extension ? (I’ve written it in the code above to illustrate the point but I know it doesn’t work).

  I hope that is enough to try and illustrate what I’m attempting.