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• How do I properly enable ffmpeg for matplotlib.animation ?

  9 novembre 2018, par spanishgum

  I have covered a lot of ground on stack so far trying to get ffmpeg going so I can make a timelapse video.

  I am on a CentOS 7 machine, running python3.7.0a0.

  python3
  
  >>> import numpy as np
  
  >>> np.__version__
  
  '1.12.0'
  
  >>> import matplotlib as mpl
  
  >>> mpl.__version__
  
  '2.0.0'
  
  >>> import mpl_toolkits.basemap as base
  
  >>> base.__version__
  
  '1.0.7'

  I found this github gist on installing ffmpeg. I used the chromium source, and installed without a prefix option (using the default).

  I have confirmed that ffmpeg is installed, although I don’t know anything about testing whether it works.

  which ffmpeg
  
  /usr/local/bin/ffmpeg
  
  
  
  ffmpeg -version
  
  ffmpeg version N-83533-gada281d Copyright (c) 2000-2017 the FFmpeg dev elopers
  
  built with gcc 4.8.5 (GCC) 20150623 (Red Hat 4.8.5-11
  
  configuration:
  
  libavutil      55. 47.100 / 55. 47.100
  
  libavcodec     57. 80.100 / 57. 80.100
  
  libavformat    57. 66.102 / 57. 66.102
  
  libavdevice    57.  2.100 / 57.  2.100
  
  libavfilter     6. 73.100 /  6. 73.100
  
  libswscale      4.  3.101 /  4.  3.101
  
  libswresample   2.  4.100 /  2.  4.100

  I tried to run a few sample examples I found online :

  [1] http://matplotlib.org/examples/animation/basic_example_writer.html

  [2] https://stackoverflow.com/a/23098090/3454650

  Everything works fine up until I try to save the animation file.

  [1]

   anim.save('basic_animation.mp4', writer = FFwriter, fps=30, extra_args=['-vcodec', 'libx264'])

  [2]

  im_ani.save('im.mp4', writer=writer)

  I found here that explictly setting the path to ffmpeg might be necessary so I added this to the top of the test scripts :

  plt.rcParams['animation.ffmpeg_path'] = '/usr/local/bin/ffmpeg'

  I tried a few more tweaks in the code but always get the same response, which I do not know how to begin deciphering :

  Traceback (most recent call last):
  
    File "testanim.py", line 27, in <module>
  
      writer.grab_frame()
  
    File "/usr/local/lib/python3.7/contextlib.py", line 100, in __exit__
  
      self.gen.throw(type, value, traceback)
  
    File "/usr/local/lib/python3.7/site-packages/matplotlib/animation.py", line 256, in saving
  
      self.finish()
  
    File "/usr/local/lib/python3.7/site-packages/matplotlib/animation.py", line 276, in finish
  
      self.cleanup()
  
    File "/usr/local/lib/python3.7/site-packages/matplotlib/animation.py", line 311, in cleanup
  
      out, err = self._proc.communicate()
  
    File "/usr/local/lib/python3.7/subprocess.py", line 836, in communicate
  
      stdout, stderr = self._communicate(input, endtime, timeout)
  
    File "/usr/local/lib/python3.7/subprocess.py", line 1474, in _communicate
  
      selector.register(self.stdout, selectors.EVENT_READ)
  
    File "/usr/local/lib/python3.7/selectors.py", line 351, in register
  
      key = super().register(fileobj, events, data)
  
    File "/usr/local/lib/python3.7/selectors.py", line 237, in register
  
      key = SelectorKey(fileobj, self._fileobj_lookup(fileobj), events, data)
  
    File "/usr/local/lib/python3.7/selectors.py", line 224, in _fileobj_lookup
  
      return _fileobj_to_fd(fileobj)
  
    File "/usr/local/lib/python3.7/selectors.py", line 39, in _fileobj_to_fd
  
      "{!r}".format(fileobj)) from None
  
  ValueError: Invalid file object: &lt;_io.BufferedReader name=6>
  
  </module>

  Is there something with my configuration that is malformed ? I searched google for this error for some time but never found anything relevant to animations / ffmpeg. Any help would be greatly appreciated.

  ---

  UPDATE :

  @LordNeckBeard pointed me here : https://trac.ffmpeg.org/wiki/CompilationGuide/Centos

  I ran into problems with installing the x264 encoding dependency. Some files in libavcodec/*.c (in the make output) were reporting undefined references to several functions. After a wild goose chase found this : https://mailman.videolan.org/pipermail/x264-devel/2015-February/010971.html

  To fix the x264 installation, I simply added some configure flags :

  ./configure --enable-static --enable-shared --extra-ldflags="-lswresample -llzma"

  ---

  UPDATE :

  So everything installed fine after fixing the libx264 problems. I went ahead and copied the ffmpeg binary from the ffmpeg_build folder into /usr/local/bin/ffmpeg.

  After running the script I was getting problems where ffmpeg could not find the libx264 shared object. I think I will have to recompile everything using different prefixes. My intuition tells me there are old files laying around after I have messed with everything, using some configuration that is broken.

  So I decided maybe I should just try to use NUX : http://linoxide.com/linux-how-to/install-ffmpeg-centos-7/
  I installed ffmpeg using the new rpm, but to no avail. I still was not able to run ffmpeg because of a missing shared object.

  Finally, instead of usiong files copied into my /usr/local/bin folder, I ran ffmpeg directly from the build bin directory. Turns out that this does work properly !

  So in essence, if I want to install ffmpeg system wide, I need to manually compile from sources again but using a nonlocal prefix.

• FFMpeg transcoding for realtime videochat via UDP

  4 septembre 2018, par Lloyd Corfex

  My problem is that I can’t find settings matching my needs.
  I know there is a tradeoff between : Speed, Quality and Size.

  (I am using a wrapper, so I can’t tell you the exact ffmpeg string but it should be comprehensible.)

  Input is always a raw video (bitmaps provided by webcam).

  CustomInputArgs = string.Format(" -pix_fmt bgr24 -video_size {0}x{1}", bitmapSize.Width, bitmapSize.Height),
  
  CustomOutputArgs = string.Format(" -vf scale=-1:{0} -maxrate 3000k -bufsize 4500k -preset ultrafast -tune zerolatency -movflags faststart", scale)

  Format : H.264

  • Speed -> ok
  • Size -> ok
  • Quality -> Not okay - Result gets "blocky" / "pixelchaos"

  
  [https://www.pic-upload.de/view-35890878/HalloPixel.jpg.html
  ]

  Format : H.265 and AVI

  • Speed -> Way too slow

  Format : FLV

  • Results in only a black screen (even if i set one of the following to the encoder)
    [https://stackoverflow.com/a/12290903/10144526]

    CustomOutputArgs = " -pix_fmt yuv420p"

    CustomOutputArgs = " -pix_fmt yuyv422"

  • As long as i have any string in the encoder outputArgs i get the following error in ffmpeg : [flv @ 03c27e40] Packet mismatch 1239459658 55255 55450

  Format MJPEG

  • Quality -> Super
  • Speed -> Ok
  • Size -> Gigantic

  Format M4V

  • Quality -> Not good
  • Speed -> Ok
  • Size -> Ok

  Format MP4

  • Conversion failed

  Does anyone has an idea about good settings ? Or can advice me in a good direction ?

• Changing Audio Volume using FFmpeg Android

  23 août 2018, par kataroty

  As I have understood, the only way to change FFmpeg volume is to do it throught a command line.

  This is what should change the volume of the audio :

  ffmpeg -i input.wav -filter:a "volume=1.5" output.wav

  Now I have used FFmpeg with command line before and it looked like this and gave me no errors :

      String[] cmd = { "-i" , pcmtowavTempFile.toString(), "-i", mp3towavTempFile.toString(), "-filter_complex", "amix=inputs=2:duration=first:dropout_transition=3", combinedwavTempFile.toString()};
  
      ffmpeg.execute(cmd, new ExecuteBinaryResponseHandler() {
  
          @Override
  
          public void onSuccess(String message) {                
  
              super.onSuccess(message);
  
              encodeWavToAAC();
  
          }
  
          @Override
  
          public void onFailure(String message) {
  
              super.onFailure(message);
  
              onError(message);
  
          }
  
      });

  But If I try to do it with audio volume in the same method, it just ignores it :

      String[] cmd = { "-i" , pcmtowavTempFile.toString(),  "-filter:a", "volume=1.3", pcmtowavTempFile.toString()};
  
      ffmpeg.execute(cmd, new ExecuteBinaryResponseHandler() {
  
          @Override
  
          public void onSuccess(String message) {
  
              super.onSuccess(message);
  
          }
  
          @Override
  
          public void onFailure(String message) {
  
              super.onFailure(message);
  
  
  
          }
  
      });

  I get neither, no success or error message with the last volume change method.

  Since the volume is there between " ", I tried adding this :

  String[] cmd = { "-i" , pcmtowavTempFile.toString(),  "-filter:a", "\"volume=1.3\"", pcmtowavTempFile.toString()};

  But the app started crashing after adding this line.