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• rv34 : use ff_mpeg_update_thread_context only when decoder is fully initialized

  21 août 2014, par Janne Grunau

  rv34 : use ff_mpeg_update_thread_context only when decoder is fully initialized
  MpegEncContext based decoders are only fully initialized after the first
  
  ff_thread_get_buffer() call. The RV30/40 decoders may fail before a frame
  
  buffer was requested. ff_mpeg_update_thread_context() fails on half
  
  initialized MpegEncContexts. Since this can only happen before a the
  
  first frame was decoded there is no need to call
  
  ff_mpeg_update_thread_context().
  Based on patches by John Stebbins and tested by John Stebbins.
  CC : libav-stable@libav.org
  

  • [DBH] libavcodec/rv34.c

• How exactly does this Jaccard distance logic (get_jaccarddist) in FFmpeg work ?

  23 mars 2024, par stilloo

  I see this C code in FFmpeg source signature_lookup file for Jaccard distance in method get_jaccarddist.

  


  If you see in the code below that is calculating for 5 BagOfWords.

  


  Now for two BagOfWords with say nothing in common intersection would be 0, that means jaccarddist would be 0, so ideally its a bad pair but this if condition jaccarddist >= sc->thworddist, would be false isn't it but we want it to be true as its bad pair ?

  


  What are the default values of sc->thworddist ?

  


  Also surprised why jaccarddist is int and not float/double ?

  


  /**
 * calculates the jaccard distance and evaluates a pair of coarse signatures as good
 * @return 0 if pair is bad, 1 otherwise
 */
static int get_jaccarddist(SignatureContext *sc, CoarseSignature *first, CoarseSignature *second)
{
    int jaccarddist, i, composdist = 0, cwthcount = 0;
    for (i = 0; i < 5; i++) {
        if ((jaccarddist = intersection_word(first->data[i], second->data[i])) > 0) {
            jaccarddist /= union_word(first->data[i], second->data[i]);
        }
        if (jaccarddist >= sc->thworddist) {
            if (++cwthcount > 2) {
                /* more than half (5/2) of distances are too wide */
                return 0;
            }
        }
        composdist += jaccarddist;
        if (composdist > sc->thcomposdist) {
            return 0;
        }
    }
    return 1;
}


  


• Systemd service (python loop -> ffmpeg stream)

  7 janvier 2019, par Kevitto

  I am currently running a stream with ffmpeg, through icecast2 through a python snippet (Fig1). I have created a systemd service to run said python script on boot (Fig2) and use a custom target (Fig3) to make sure it loads once every other service is loaded, mostly for icecast2.

  I’ve conducted multiple tests, and the stream works fine if launched either from the python code or if I restart the service attached to it.

  My problem is, on a (re)boot of the system, the service runs for approximately 15 seconds, then the stream dies. I’ve read so much on python and systemd, but I can’t for the life of me figure out where the problem lies. I’ve tried changing my python code, the unit load order and anything else I found online that could help, but found nothing.

  Fig1 (dxstream.py)

  import sys
  
  import time
  
  import subprocess
  
  
  
  def start():
  
      return subprocess.Popen(r’ffpmeg -re -f alsa -ac2 -i hw:1,0 -acodec mp3 -ab 320k -f mp3 icecast://sourcehackme@localhost:8000/stream', shell=True)
  
  
  
  testProcess = start()
  
  
  
  while True:
  
  
  
      res = testProcess.poll()
  
      if res is not None:
  
          testProcess = start()
  
      time.sleep(1)

  Fig2 (dxstream.service)

  [Unit]
  
  Description=ffmpeg stream starter
  
  After=multi-user.target
  
  [Service]
  
  Type=idle
  
  Execstart=/usr/bin/python /usr/local/bin/dxstream.py
  
  Restart=on-failure
  
  
  
  [Install]
  
  WantedBy=custom.target

  Fig3 (custom.target)

  [Unit]
  
  Description=Custom Target
  
  Requires=multi-user.target
  
  After=multi-user.target
  
  AllowIsolate=yes