Recherche avancée

Sur d’autres sites (8691)

• Trouble saving matplotlib animation with ffmpeg

  21 avril 2017, par kevinkayaks

  I installed ffmpeg and would like to save an animation.

  My code is

  #evo is the dataset composed of sequence of images
  
  
  
  evo = np.load('bed_evolution_3000iter_2.npy')
  
  fig = plt.figure(figsize=(15,15*2*width/length))
  
  # make axesimage object
  
  # the vmin and vmax here are very important to get the color map correct
  
  im = plt.imshow(np.transpose(evo[0]), cmap=plt.get_cmap('jet'), vmin=0, vmax=1300)
  
  cbar_ax = fig.add_axes([0.85, 0.15, 0.05, 0.7])
  
  fig.colorbar(im, cax=cbar_ax)
  
  fig.subplots_adjust(right=0.8)
  
  
  
  def updatefig(j):    
  
      # set the data in the axesimage object
  
      im.set_array(np.transpose(evo[j]))
  
      # return the artists set
  
      return im,
  
  # kick off the animation
  
  ani = animation.FuncAnimation(fig, updatefig, frames=range(len(evo)), 
  
                            interval=100, blit=True)
  
  
  
  #now just need to get the ability to save... this uses 
  
  
  
  FFwriter = animation.FFMpegWriter()
  
  ani.save('basic_animation.mp4', writer = FFwriter, fps=30, extra_args =([vcodec', 'libx264'])

  The animation runs and it looks good, but I just can’t get it to save. The error message (at this stage) is

  

  I am not sure what’s going wrong. Any help is appreciated.

  EDIT :
  Following Can’t save matplotlib animation I added

  plt.rcParams['animation.ffmpeg_path'] ='C:\\Program Files\\ffmpeg  \\bin\\ffmpeg.exe'

  Which returns
  Warning : Cannot change to a different GUI toolkit : qt. Using qt4 instead.
  ERROR : execution aborted

• How to get webam frames one by one but also compressed ?

  29 mars, par Vorac

  I need to grab frames from the webcam of a laptop, transmit them one by one and the receiving side stitch them into a video. I picked ffmpeg-python as wrapper of choice and the example from the docs works right away :

  


  #!/usr/bin/env python

# In this file: reading frames one by one from the webcam.


import ffmpeg

width = 640
height = 480


reader = (
    ffmpeg
    .input('/dev/video0', s='{}x{}'.format(width, height))
    .output('pipe:', format='rawvideo', pix_fmt='yuv420p')
    .run_async(pipe_stdout=True)
)

# This is here only to test the reader.
writer = (
    ffmpeg
    .input('pipe:', format='rawvideo', pix_fmt='yuv420p', s='{}x{}'.format(width, height))
    .output('/tmp/test.mp4', format='h264', pix_fmt='yuv420p')
    .overwrite_output()
    .run_async(pipe_stdin=True)
)


while True:
    chunk = reader.stdout.read(width * height * 1.5)  # yuv
    print(len(chunk))
    writer.stdin.write(chunk)


  


  Now for the compression part.

  


  My reading of the docs is that the input to the reader perhaps needs be rawvideo but nothing else does. I tried replacing rawvideo with h264 in my code but that resulted in empty frames. I'm considering a third invocation looking like this but is that really the correct approach ?

  


  encoder = (                                                                     
    ffmpeg                                                                      
    .input('pipe:', format='rawvideo', pix_fmt='yuv420p', s='{}x{}'.format(width, height))
    .output('pipe:', format='h264', pix_fmt='yuv420p')                          
    .run_async(pipe_stdin=True, pipe_stdout=True)                               


  


• FFMPEG Dash with tiles of thumbnail images

  31 juillet 2020, par martyn Gilbert

  As of DASH-IF IOP version 4.2, section 6.2.6 defines the notion of image-based tracks in DASH :
https://dashif.org/docs/DASH-IF-IOP-v4.3.pdf.

  



  This is the ability to have an adaption set made up of mime type images that themselves are a strip of low resolution thumbnails. 
A player will use these thumbnails when the user hovers their mouse over the video timeline and get a 
preview of the the frame at that approximate timecode.

  



  Theo player website has a page dedicated to this function for playback :
https://www.theoplayer.com/blog/in-stream-thumbnail-support-dvr-dash-streams

  



  I need to generate a dash stream (not live) using ffmpeg that also contains these thumbnails. 
I already have an ffmpeg command that will generate the film strip of jpgs which outputs a thumbnail every 5 seconds of input video and joins 5 of these together in a single jpg :

  



  ffmpeg -i INPUT -q:v 20 -vf "select=not(mod(n\,125)),scale=480:270,tile=5x1" -vsync vfr output%d.jpg

  



  and the mpeg dash itself :

  



  ffmpeg -i INPUT -y -map 0 -acodec aac -ac 2 -ar 48000 -s 960x540 -vcodec libx264 -f dash -preset veryfast -b:v:2 1500k -seg_duration 2 output.mpd

  



  But I cannot find a way in ffmpeg to include the thumbnails in the dash mpd file.