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

  7 mars 2017, 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] http://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.

• avcodec/h264, videotoolbox : fix crash after VT decoder fails

  21 février 2017, par Aman Gupta

  avcodec/h264, videotoolbox : fix crash after VT decoder fails
  The way videotoolbox hooks in as a hwaccel is pretty hacky. The VT decode
  
  API is not invoked until end_frame(), so alloc_frame() returns a dummy
  
  frame with a 1-byte buffer. When end_frame() is eventually called, the
  
  dummy buffer is replaced with the actual decoded data from
  
  VTDecompressionSessionDecodeFrame().
  When the VT decoder fails, the frame returned to the h264 decoder from
  
  alloc_frame() remains invalid and should not be used. Before
  
  9747219958060d8c4f697df62e7f172c2a77e6c7, it was accidentally being
  
  returned all the way up to the API user. After that commit, the dummy
  
  frame was unref’d so the user received an error.
  However, since that commit, VT hwaccel failures started causing random
  
  segfaults in the h264 decoder. This happened more often on iOS where the
  
  VT implementation is more likely to throw errors on bitstream anomolies.
  
  A recent report of this issue can be see in
  
  http://ffmpeg.org/pipermail/libav-user/2016-November/009831.html
  The issue here is that the dummy frame is still referenced internally by the
  
  h264 decoder, as part of the reflist and cur_pic_ptr. Deallocating the
  
  frame causes assertions like this one to trip later on during decoding :
    Assertion h->cur_pic_ptr->f->buf[0] failed at src/libavcodec/h264_slice.c:1340
  With this commit, we leave the dummy 1-byte frame intact, but avoid returning it
  
  to the user.
  This reverts commit 9747219958060d8c4f697df62e7f172c2a77e6c7.
  Signed-off-by : wm4 <nfxjfg@googlemail.com>
  

  • [DH] libavcodec/h264_refs.c
  • [DH] libavcodec/h264dec.c
  • [DH] libavcodec/version.h
  • [DH] libavcodec/videotoolbox.c

• Javascript, method chaining, how to realize response in callback ?

  12 avril 2017, par CHBS

  Good afternoon, ladies and gentlemen.
  I write for myself a module on node js, I can not implement the save () function

  module.exports = function(filename, callback){
  
      this.callback = callback(require(filename));
  
      return { 
  
          save: function() {
  
              console.log(this);
  
              //fs.writeFile(filename, 'Hello Node.js');
  
          }
  
      }; 
  
  }
  
  
  
  File('file.json', function(data){
  
      data['blablabla'] = 12345;
  
  }).save();

  How from a callback, to transfer the changed copy of a file in save (), and there already to save it through fs ?
  I’m interested in the implementation of the fluent-ffmpeg function save ()

  ffmpeg('/path/to/file.avi')
  
   .videoCodec('libx264')
  
   .audioCodec('libmp3lame')
  
   .size('320x240')
  
   .on('error', function(err) {
  
     console.log('An error occurred: ' + err.message);
  
   })
  
   .on('end', function() {
  
     console.log('Processing finished !');
  
   })
  
   .save('/path/to/output.mp4');

  And as well as implemented on() ?

  on('end'),   
  
  on('error'),   
  
  on('response'),

  I will be grateful for the information provided.