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• ffplay startup time proportional to specified framerate

  17 décembre 2019, par bremen_matt

  I am playing a video over http using ffplay. The call I am using looks like this :

  ffplay -framerate 30 -fflags nobuffer -flags low_delay -autoexit -i http://localhost:8880

  The video is an H.264 encoding where (my understanding is a bit unclear here) it is something like a "raw" H.264 stream without timestamps.

  My primary concern is to get video displayed with low latency. In that regard, the video is fine.

  The issue is with the framerate and with the startup time.

  The video source is emitting frames as soon as they are processed, so the frame rate is not constant. However, my experience is that as long as you specify a framerate larger than the max achievable frame rate of the source, then the viewer still looks fine. On the flipside, if the video source starts emitting frames at 60 fps, but I specify a framerate of 30, then the delay just sort of builds up in ffplay to the point where after 10 seconds, the video is 20 seconds behind. So the first question would be whether there is a way to get ffplay to use a variable framerate. The behavior I am looking for is "display a frame as soon as it is received over http".

  In light of the aforementioned issue, the approach I have been taking is to simply specify a high framerate, which seems to work. However, there is an issue with this approach in the form of startup time. When I set the framerate to 10, the ffplay window starts in approx 3 seconds, but then quickly starts accruing a lag (so I can’t do this). When I set the framerate to 100, the ffplay window takes 30 seconds (literally 30 seconds) to start, but then will not have any lag.

  I have seen that ffmpeg has a vsync option that on the surface seems like it would allow you to set a variable framerate. However, ffplay doesn’t seem to recognize this. I would also be willing to pipe the output of ffmpeg to a different window (I am running Ubuntu 18.04) if that is what must be done, but I would prefer not to have to recompile ffplay.

• How to accurately detect the start of the main beat and soundtracks in diverse audio tracks ?

  18 juin 2024, par SnoofFloof

  I'm working on a project where I need to edit soundtracks. The challenge is to detect when the main beat and melody of any given soundtrack is properly developed. I am certain there is better terminology to describe what I am aiming for, but ideally, I want to skip the "build-up" and immediately have the song starting at the "main part". This needs to work for various songs across different genres, which often have different structures and onset patterns, making it difficult to streamline the process.

  


  For example :

  


  https://www.youtube.com/watch?v=P77CNtHrnmI -> I would want to my code to identify the onset at 0:24

  


  https://www.youtube.com/watch?v=OOsPCR8SyRo -> Onset detection at 0:12

  


  https://www.youtube.com/watch?v=XKiZBlelIzc -> Onset detection at 0:19

  


  I've tried using librosa to analyze the onset strength and detect beats, but the current implementation either detects the very beginning of the song or fails to consistently identify when the beat is fully developed.

  


  This was my approach ;

  


  def analyze_and_edit_audio(input_file, output_file):
    y, sr = librosa.load(input_file)
    tempo, beat_frames = librosa.beat.beat_track(y=y, sr=sr)
    beat_times = librosa.frames_to_time(beat_frames, sr=sr)
    main_beat_start = beat_times[0]


  


  I have very little experience with librosa/audio editing, so I would appreciate any suggestions you might have !

  


• HEVC File bigger after converting from h264

  26 janvier 2019, par Aaroknight

  I’m currently working an an automated Python script for indexing and converting all my movies and episodes with ffmpeg. I use subprocess.call() for running the ffmpeg command and tested this command with some movies. As expected the big h264 files were converted to merely one third of what they used to have.

  But now that I was testing the method I found that a converted episode (about 400MB in h264) had over 1,6GB in hevc. I have absolutely no idea why the new file would be that much bigger in hevc.
  This is my code :

  def convert(path):
  
      outvid = path.strip(".mkv") + "h265.mkv"
  
  
  
      cmd = ["ffmpeg", "-i", path, "-map", "0", "-map_metadata", "0", "-map_chapters", "0", "-c:v", "libx265",
  
             "-c:a", "copy", "-c:s", "copy", "-preset", "ultrafast", "-x265-params", "lossless=1", outvid]
  
      subprocess.call(cmd)
  
  
  
  convert("/Volumes/2TB/Black Butler/Season 1/Black Butler S01E01.mkv")

  I don’t have that much experience with ffmpeg, nor with subprocess. This is one of my first bigger projects. I hope someone can tell me what the problem might be.

  UPDATE
  Problem applies only for small video files. I now just check for the file size and skip the small files. Wouldn’t have made much of a difference anyway.