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• FFMPEG Dash with tiles of thumbnail images

  31 juillet 2020, par martyn Gilbert

  As of DASH-IF IOP version 4.2, section 6.2.6 defines the notion of image-based tracks in DASH :
https://dashif.org/docs/DASH-IF-IOP-v4.3.pdf.

  



  This is the ability to have an adaption set made up of mime type images that themselves are a strip of low resolution thumbnails. 
A player will use these thumbnails when the user hovers their mouse over the video timeline and get a 
preview of the the frame at that approximate timecode.

  



  Theo player website has a page dedicated to this function for playback :
https://www.theoplayer.com/blog/in-stream-thumbnail-support-dvr-dash-streams

  



  I need to generate a dash stream (not live) using ffmpeg that also contains these thumbnails. 
I already have an ffmpeg command that will generate the film strip of jpgs which outputs a thumbnail every 5 seconds of input video and joins 5 of these together in a single jpg :

  



  ffmpeg -i INPUT -q:v 20 -vf "select=not(mod(n\,125)),scale=480:270,tile=5x1" -vsync vfr output%d.jpg

  



  and the mpeg dash itself :

  



  ffmpeg -i INPUT -y -map 0 -acodec aac -ac 2 -ar 48000 -s 960x540 -vcodec libx264 -f dash -preset veryfast -b:v:2 1500k -seg_duration 2 output.mpd

  



  But I cannot find a way in ffmpeg to include the thumbnails in the dash mpd file.

  


• Revision 31957 : légère amélioration ... Un peu de documentation dans le code également

  7 octobre 2009, par kent1@… — Log

  légère amélioration ...
  Un peu de documentation dans le code également

• ALSA lib pcm.c:7963 :(snd_pcm_recover) underrun occurred with MoviePy

  25 janvier 2017, par mdornfe1

  So I have a bit of an unusual use case for MoviePy. I have a 40 core computer, and on each core I’m creating a moviepy object, having that object connect to an mp4 file, then having each object decompress random images from the mp4 file. I’m doing this so I can use the images to train a neural network. It actually works really except I’m getting this warning

  ALSA lib pcm.c:7963:(snd_pcm_recover) underrun occurred

  I can’t figure out its source. Here is a basic code example

  from moviepy.editor import VideoFileClip
  
  from queue import Queue, deque
  
  import threading, multiprocessing
  
  import numpy as np
  
  
  
  def decompress_worker(training_data:Queue, frame_idxs:Queue, video_file_path:str):
  
      """
  
      Eache of these workers will pop off one integer from frame_idxs.
  
      It will then decompress that frame number from vs. Finally
  
      it will store the decompressed image in training_data.
  
      """
  
      vs = VideoFileClip(video_file_path)
  
      fps = vs.fps
  
  
  
      while frame_idxs.qsize() > 0:
  
          frame_number = frame_idxs.get()
  
          frame = vs.get_frame( frame_number / fps )
  
          training_data.put(frame)
  
  
  
  
  
  num_cores = multiprocessing.cpu_count()
  
  frame_idxs = Queue()
  
  training_data = Queue()
  
  frame_idxs.queue = deque(np.random.randint(0, 10000, size = 1000))
  
  
  
  decompress_threads = []
  
  for n in range(num_cores):
  
      decompress_thread = threading.Thread(target=decompress_worker, 
  
          args=(training_data, frame_idxs, video_file_path))
  
      decompress_threads.append(decompress_thread)
  
      decompress_thread.start()
  
  
  
  [thread.join() for thread in decompress_threads]

  I’m guessing it’s coming from me reading data from the mp4 file to fast ? It would be nice if I could just suppress the warning. Is there a way to do that ?