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• lavu/tx : invert permutation lookups

  27 février 2021, par Lynne

  lavu/tx : invert permutation lookups
  out[lut[i]] = in[i] lookups were 4.04 times(!) slower than
  
  out[i] = in[lut[i]] lookups for an out-of-place FFT of length 4096.
  The permutes remain unchanged for anything but out-of-place monolithic
  
  FFT, as those benefit quite a lot from the current order (it means
  
  there's only 1 lookup necessary to add to an offset, rather than
  
  a full gather).
  The code was based around non-power-of-two FFTs, so this wasn't
  
  benchmarked early on.
  

  • [DH] libavutil/tx.c
  • [DH] libavutil/tx_priv.h
  • [DH] libavutil/tx_template.c

• Piping ffmpeg output into ffplay stdin with boost

  21 décembre 2020, par botiapa

  I'm trying to pipe the output of an ffmpeg process into an ffplay process (Sort of like a playback). My problem is the following : If I copy the output character by character (by character I mean char) it works correctly, other than it consuming a whole lot of cpu power. However when I try to pipe chunks into it (by using a buffer), ffplay for some reason doesn't even recognize the input.

  


  bp::ipstream iso;
bp::ipstream ise;
bp::opstream in;
    
bp::child ffmpeg(bp::search_path("ffmpeg"), bp::args({"-loglevel", "quiet", "-f", "pulse", "-i", "default", "-f", "wav", "-bitexact", "-nostdin", "-"}), bp::std_out > iso, bp::std_err > ise);
bp::child ffplay(bp::search_path("ffplay"), bp::args({"-loglevel", "verbose", "-nodisp", "-f", "wav", "-i", "-"}), bp::std_in < in, bp::std_out > bp::null);


  


  Here are the 2 code snippets for comparison :

  


  Here it is copying char by char

  


  while(ffmpeg.running()) {
    char c;
    c = iso.get();
    in << c;
}


  


  And here it is copying with the help of a buffer

  


  char buffer[1024];
while(ffmpeg.running()) {
    iso.get(buffer, 1024);
    in << buffer;
}


  


  I can provide ffplay output if necessary, however I didn't see any errors or things like that.

  


• Generating thumbnails from multiple videos on Desktop, using ffmpeg, or something similar

  6 février 2013, par Birk

  Hi guys this is a long shot but here goes...

  I basically have what I mentioned in the title running on my server. When I upload a video ffmpeg decomplies it and gives me screenshots, then I pick a screenshot that I want to use for that video. Currently, my server can process 3 videos at a time. The down side is that this uses up A LOT of the server processing power. :(

  Is there a way, or a program, that can process several video at a time and generate me screenshots on my Desktop ? If this is possible then I can just use my spare computer here to process everything then upload the screenshots/video to my server.

  This is what I basically have running now on the server. kayweb.com.au/blogs/Web-Development/Generating-screenshots-using-FFmpeg

  Something like this, But this thumbnail generator puts everything into one image. I need to be able to choose with thumbnail I want to use.
  http://www.tothepc.com/archives/make-movie-caps-screenshots-with-free-video-thumbnails-maker/

  Anyone have any suggestions ?