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• Input seeking for frame at specified timestamp with Py-AV

  9 décembre 2019, par neonScarecrow

  I have a project already using Py-AV and am trying to replicate a specific ffmpeg command. The goal is to get a frame roughly around the specified timestamp.

  Here’s the ffmpeg commmand :
  https://trac.ffmpeg.org/wiki/Seeking

  ffmpeg -ss 14 -i https://some_url.mp4 -frames:v 1 frame_at_14_seconds.jpg

  Here’s my code :

      #return one frame around 14 seconds into the movie
  
      target_sec = 14 
  
      container = av.open('https://some_url.mp4', 'r')
  
      container.streams.video[0].thread_type = 'AUTO'
  
      video_stream = next(s for s in container.streams if s.type == 'video')
  
      time_base = float(video_stream.time_base)
  
      target_timestamp = int(target_sec / time_base) + video_stream.start_time
  
      video_stream.seek(target_timestamp)
  
      for frame in container.decode(video_stream):
  
          frame.to_image().save('frame_at_14_seconds.jpg')
  
          break

  Additionally, I have found any documentation about this, but does anyone know if either command (ffmpeg/av.open) is downloading the entire file to a tmp file behind the scenes. I’m looking for a less memory-intensive way to read a frame for every second in an up to 60 second video.

• How to estimate I frame motion degree ?

  7 mars 2013, par Greper

  I am measuring video quality using the video's I frames. But　I found some I frames contains motion,for example a dancing MV. As a result it is inaccurate to measure the sharpness of a video according to these kind of I frames. How can I eliminate these kind of I frames ? Can FFMPEG provide some information to estimate the motion degree of the I frame ? I thought of useing I frame and its subsequent P frames's motion vector to estimate the motion degree of the current I frame. But I am not familar with ffmpeg, don't know how to estimate the motion degree of I frame. Thanks for any help.

• avformat/ftp: Fix for invalid use of av_strtok

  18 avril 2020, par Limin Wang

  avformat/ftp: Fix for invalid use of av_strtok
  By the av_strtok() description :
  
   * On the first call to av_strtok(), s should point to the string to
  
   * parse, and the value of saveptr is ignored. In subsequent calls, s
  
   * should be NULL, and saveptr should be unchanged since the previous
  
   * call.
  Signed-off-by : Limin Wang <lance.lmwang@gmail.com>
  

  • [DH] libavformat/ftp.c