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• Use ffmpeg to compile RGBA image sequence into two separate videos (RGB + Alpha)

  27 novembre 2018, par MirceaKitsune

  I plan on using Blender to render animated sequences for a game. I need the videos to have transparent backgrounds in the format expected by its engine. This format involves the transparency being defined as a separate grayscale video of equal FPS and duration. Since splitting the RGB and Alpha channels in Blender is more complicated, I’d prefer doing this directly from ffmpeg.

  The input directory contains an image sequence of png files in RGBA format (eg : 0000.png to 0100.png). What I need ffmpeg to do is compile them into two separate videos : One containing only the RGB channels (leave transparency black) and another containing only the grayscale alpha channel. In the end I’d have something like my_video.mp4 + my_video_mask.mp4.

  I’m familiar with compiling non-transparent image sequences into video using :

  ffmpeg -f image2 -i /path/to/sequence/%04d.png output.mp4

  But I don’t know how to extract the alpha channel and make it a separate video file. What is the simplest ffmpeg command to achieve this result ?

• moviepy problem with audio export : AttributeError : 'FFMPEG_AudioWriter' object has no attribute 'proc'

  3 novembre 2018, par Jaivin Wylde

  In this example, I need to create an audio export for speech recognition.

  clips = moviepy.editor.concatenate_videoclips(videoPart, method="compose")
  
  
  
  clips.audio.write_audiofile("Clips/", game.replace(" ", "_") +
  
                              "/audio_export.mp3", verbose=False, codec="libmp3lame")

  Then I get this error message.

  Traceback (most recent call last):
  
  File "/usr/local/lib/python3.5/dist-packages/moviepy/audio/io/ffmpeg_audiowriter.py", line 134, in __del__
  
  self.close()
  
  File "/usr/local/lib/python3.5/dist-packages/moviepy/audio/io/ffmpeg_audiowriter.py", line 122, in close
  
  if self.proc:
  
  AttributeError: 'FFMPEG_AudioWriter' object has no attribute 'proc'

  I would appreciate any help, thank you.

• SteamVR creating loading screen flicker when recording using FFMPEG in unity

  28 octobre 2018, par Mohamed Muzammil

  I have a heatmap plugin integrated in my Unity VR game(with SteamVR). The plugin uses eye tracking information to generate live heatmaps as the user gazes at different elements in the game. As the heatmaps are generated, the whole camera view(user’s) is overlayed with heatmaps info and written to a MP4 file using FFMPEG.

  ---

  The whole process works fine. But I have an annoying problem where during the recording the user’s camera view is not stable and keeps flickering and stops only when the recording is stopped. It interrupts the smooth flow of his game
  For now, I’ve narrowed down the code which causes the trouble,

          public void Write(byte[] data)
  
      {
  
          if (_subprocess == null) return;
  
  
  
          _stdin.Write(data);
  
          _stdin.Flush();
  
      }

  From my understanding, It is in this part of the code stdinput is invoked to write to the file system. So, I surmise that the problem must be with accessing the file system which in turn must have caused some time delay when each frame is written in the update method. Correct me if i am wrong here.
  

  The loading screen which appears during every frame write looks something like above. It interrupts the smooth flow of the game and also makes the recording useless as the user keeps focusing on the flicker rather than the actual objects of interest. I would really be grateful if someone shows light on the issue here ?