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• ffmpeg - seamless crossfade loop for the part of video

  14 janvier 2021, par Flamin GO

  I need to apply crossfade to the last X frames of a video with the first X frames in order to obtain a seamless loop, but making this for the necessary part of video.

  


  Here's the answer for looping the entire video.

  


  Currently what I have :
(Whole video duration = 25. Cutted (result) part = 15 sec (from 5 to 20 sec pos). Transition = 1 sec.)

  


  ffmpeg -i input.mp4 -ss 5 -to 20 -filter_complex
    "[0]split[body][pre];
     [pre]trim=duration=1,format=yuva420p,fade=d=1:alpha=1,setpts=PTS+( (15+(5-1)) /TB)[jt];
     [body]trim=1,setpts=PTS-STARTPTS[main];
     [main][jt]overlay"  -c:v libx264 -preset veryslow -b:v 2500K output.mp4
 


  


  In this case, everything works, but at the end of the resulting video, a piece from the original video is superimposed, which starts from 0 to 1 second, and not from 4 to 5 seconds of the original video, as it should be.

  


  I read the official ffmpeg documentation, tried some actions on "start/end" parameters for "trim/fade" with changing of "setpts", but I always got just another batch of bugs.

  


• Why the output of the ffmpeg-python doesn't match the image shape ?

  9 novembre 2019, par Swi Jason

  I used the ffmpeg-python module to convert video to images. Specifically, I used the code provided by the official git repo of ffmpeg-python, as below

  out, _ = (
  
      ffmpeg
  
      .input(in_filename)
  
      .filter('select', 'gte(n,{})'.format(frame_num))
  
      .output('pipe:', vframes=1, format='image2', vcodec='mjpeg')
  
      .run(capture_stdout=True)
  
  )
  
  im = np.frombuffer(out, 'uint8')
  
  print(im.shape[0]/3/1080)
  
  # 924.907098765432

  The original video is of size (1920, 1080) and pix_fmt ’yuv420p’, but the outputs of the above code is not 1920.

  I have figured out by myself that the output of ffmpeg.run() is not a decoded image array, but a byte string encoded by JPEG format. To restore the image into a numpy array, simply use the cv2.imdecode() function. For example,

  im = cv2.imdecode(im, cv2.IMREAD_COLOR)

  However, I can’t use opencv on my embeded Linux system. So my question now is that, can I get numpy output from ffmpeg-python directly, without the need of converting it by opencv ?

• Displaying an AVFrame on the screen with SDL 2.0

  22 septembre 2013, par jsp99

  I am working on some code with the help of this tutorial and using the latest development libraries of ffmpeg and SDL. I am stuck at the point where I have to display the decoded frame (AVFrame) on the screen. I am inclined to do the above task i.e, Displaying the AVFrame on screen using the latest API of SDL 2.0 (Using Renderers and Textures alongside the usage of SDL_Window). Frankly speaking, I am not an expert in SDL_Renderer, SDL_Texture and the functions associated with them. But I am reading the documentation in the official site of SDL 2.0 and working my way through them.

  Is there a way to do the following using SDL 2.0 API :

  • Convert the native frame format to a flavour of YUV and display it.

    (OR)

  • If it is possible, display the frame without having to convert it from native format.

  I want to do the above using Renderers and Textures. There doesn't seem to be an easy way to work with them.

  Can anyone guide me through the steps to do the above tasks ?

  PS : Though I have not explicitly tried it, I came across some ways to display AVFrame on the screen by converting the AVFrame format(native) to RGB. But I do not want the native frame format (which is mostly YUV) to RGB conversion, as it is computationally expensive.

  Converting between formats is done by sws_scale()