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• save row ffmepg data packets as a video

  7 août 2019, par MattéoLuci

  I have modified the muxing.c ffmpeg example program to be able to save a video from the PC or on an RTSP stream, and it works quite good.
  I would like to make the video saving as fast and efficient as possible by saving directly the packets without changing them into AVFrames (I don’t need to print them).

  I tried to save the AVPacket coming from av_read_frame(InFmtCtx, &packet) with av_write_frame(OutFmtCtx, &packet).

  AVPacket packet;
  
  static int count = 0;
  
  while (av_read_frame(InFmtCtx, &packet)>=0) {
  
     if(packet.stream_index == videoStream) {
  
  
  
         packet.dts = count;
  
         packet.pts = count++;
  
  
  
         av_packet_rescale_ts(&packet, ost->enc->time_base, 
  
                                           ost->st->time_base);
  
         packet.stream_index = ost->st->index;
  
         if (av_write_frame(OutFmtCtx, &packet) < 0) {
  
            fprintf(stderr, "Error writing video frame: \n");
  
            exit(1);
  
         }
  
         ost->enc->frame_number++;
  
     }
  
  }

  The program runs correctly and the video file has the right size and the right duration.
  When I run it with VLC or ffmpeg it shows no error message, the time runs correctly, but no image is printed

• Can only save animation in matplotlib with default parameters

  20 août 2019, par J.Doe

  I keep getting this error when trying to save my animations in matplotlib :

  import numpy as np
  
  import matplotlib.pyplot as plt
  
  from matplotlib.animation import FuncAnimation
  
  
  
  plt.rcParams['animation.ffmpeg_path'] = 'C:\FFmpeg\bin'
  
  
  
  fig, ax = plt.subplots()
  
  ax.set_xlim(-0.1 ,2*np.pi + 0.1)
  
  ax.set_ylim(-1.1 ,1.1)
  
  ln, = plt.plot([], [], '-')
  
  
  
  x = np.linspace(0,2*np.pi,1000)
  
  
  
  def update(frame):
  
  
  
      y = frame*np.sin(x)
  
      ln.set_data(x,y)
  
      return ln,
  
  
  
  ani = FuncAnimation(fig,
  
                      update,
  
                      frames=np.linspace(1,-1,1000),
  
                      interval=1000/144)
  
  
  
  ani.save('lol.gif')

  MovieWriter ffmpeg unavailable. Trying to use pillow instead.

  This is a repetition of an unanswered question : UserWarning : MovieWriter ffmpeg unavailable

  I tried running a sample code from here, but it still says ffmpeg isn’t available, even though I installed and activated it according to wikihow. So even setting the path to the binary doesn’t seem to work.

  I can’t set the fps or the dpi, or anything since the save function just defaults. What can I do so that python finally starts using ffmpeg ?

• How to save video as memory stream to .m4s freagments ?

  13 septembre 2019, par Yehor Chankov

  Summary

  I have a video streaming application, that processes videos uploaded by a user and serves it back to the user. Previously a user had to wait until the whole video had been processed and could only access it after that. Now I want my users to be able to start watching a video as soon as the first fragment is processed.

  The main idea is that I have an mp4 file, that I upload in memory using python and store as a 4d numpy array. Then I divide it into separate chunks and process each chunk.

  Solutions so far

  All solutions that I found so far are based on the idea that a complete mp4 video file exists, so that m4s fragments can be created by dividing it.

  Expected result

  What I want to achieve is that after each chunk is processed, it gets saved from memory to disk as m4s fragment, that can be served to a user immediately via MPEG dash .mpd playlist that links to all these fragments on disk.