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• ffmpeg how to extract X frames every Y interval from url efficiently

  13 décembre 2018, par Luay Gharzeddine

  I’m trying to gather data for a datascience project, and am downloading frames from online videos using ffmpeg. I want to download a subset of the frames in the video, without needing to be precise about which, the only requirement is that they are reasonably spaced apart from each other.

  I have tried

  ffmpeg -i "http://www.somevideo.com" -r 1 -f image2 "image%06d.jpg"

  and

  ffmpeg -i "http://www.somevideo.com" -vf fps=1 "image%06d.jpg"

  and eventually found the following method

  ffmpeg -ss offset1 -i "http://www.somevideo.com" -ss offset2 -i "http://www.somevideo.com" -map 0:v -frames:v 10 -start_number 0 "image%06d.jpg" -map 1:v -frames:v 10 -start_number 10 "image%06d.jpg"

  and all work, but are slow. I have found a hack where I run the following command multiple times, at different offsets, and it seems to be the fastest (where each ffmpeg command is run in parallel multithreaded)

  ffmpeg -ss offset -i "http://www.somevideo.com" -vframes frames_per_fragment -an -start_number start_index "image%06d.jpg"

  this about 25% faster than the previous method

  Is there a faster way to do this ? The issue is that downloading over a network is a bottleneck, so I want to download only the frames I need. I’m looking to download videos/frames in bulk, so any speed improvement would be helpful.

• FFMPEG -f segment and FFPROBE keyframes are different

  18 juillet 2019, par user2190197

  I have a online video editor. And i want fast strip and concat mp4 files. For this i use code like this :

  For get keyframes :

  exe_ffprobe("-select_streams v -skip_frame nokey -show_frames -show_entries frame=pkt_pts_time,pict_type $input_file");

  Sample Result :

  array (
  
    0 => '0.083417',
  
    1 => '2.085419',
  
    2 => '4.170838',
  
  ...
  
    12 => '24.149149',
  
    13 => '26.234568',
  
    14 => '27.569236',       < Why ffmpeg missed this keyframe?
  
    15 => '29.654655',
  
  ...
  
    230 => '466.966967',
  
    231 => '469.052386',
  
    232 => '471.137804',
  
    233 => '473.223223',
  
    234 => '475.308642',
  
    235 => '477.394061',
  
    236 => '479.479479',
  
  )
  
  ...

  For split video :

  exe_ffmpeg("-y -i $input_file -c copy -map 0 -segment_list segments.csv -f segment -reset_timestamps 1 path/to/%d.mp4");

  Sample result :

  0.mp4,0.000000
  
  1.mp4,2.085419
  
  2.mp4,4.170838
  
  ...
  
  12.mp4,24.149149
  
  13.mp4,26.234568
  
  14.mp4,29.654655
  
  15.mp4,31.740073
  
  ...
  
  230.mp4,475.308642
  
  231.mp4,477.394061
  
  232.mp4,479.479479
  
  end

  But count of keyframes from ffprobe, and count splitted videos are different.

  So how i can segment or get keyframes correctly, to match the count

  Also, keyframes and segments.csv are differently too, but more of keyframes has correct timestamps

• Exporting MPEG Transport Stream (.ts) keyframes to images in C/C++ ? Libavcodec / FFMPEG ?

  11 mai 2021, par CyberBully2003

  I have some buffers made up of 188 byte TS packets. When I write them to a file, I can successfully view these .ts files in a video player. MPEG-2/H.264 is the format of the Transport Streams.

  


  Now, I would like to export the keyframes from these Transport Streams buffers (or .ts files) as .jpeg or some other common image format in my C/C++ project.

  


  This is a trivial task from the command line using ffmpeg, where I just feed it the .ts file and some parameters.

  


  However, for the purpose of this project, I would like to accomplish this conversion/exporting of keyframes as images code-side in my current C/C++ directory because the raw bytes from these generated images will be put into another format.

  


  People online seem to recommend using libavcodec. There is an mpegets file in the ffmpeg source that seems like it might have some of the backend to do what I want.

  


  However, the steps needed to achieve this task using the library is not apparent.

  


  I know I could call ffmpeg from C++ and use stdin, but this isn't a preferred solution for this project.

  


  If someone could give me some guidance (and even better some example code) to accomplish this task, it would be greatly appreciated !