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• What does matplotlib need to know about ffmpeg's installation

  8 décembre 2016, par fffred

  My installation of ffmpeg and matplotlib seem to be problematic :

  In [9]: matplotlib.animation.writers["ffmpeg"]
  
  ---------------------------------------------------------------------------
  
  RuntimeError                              Traceback (most recent call last)
  
   ........
  
       58     def __getitem__(self, name):
  
       59         if not self.avail:
  
  ---> 60             raise RuntimeError("No MovieWriters available!")
  
       61         return self.avail[name]
  
       62 
  
  
  
  RuntimeError: No MovieWriters available!

  It looks like ffmpeg (or any other writer) has not been found. However, I have built it from source and installed it in ~/.local. This is included in the $PATH, and I verified that the command ffmpeg is working from the terminal.

  Is there something I should watch out when installing ffmpeg ? Is there something else to do ?

  Config :

  • Python 2.7.3
  • matplotlib 1.2.0
  • ffmpeg N-82786-gc188f35
  • Red Hat 6.7

  Note : I would like to avoid re-installing everything from scratch. I do not have root access and the only thing I installed manually is ffmpeg.

• How to calculate the "Range" header for mp4 file to play/download a part of it ? [youtube-dl]

  5 décembre 2016, par supersan

  I’m using youtube-dl to download videos from YouTube. Unfortunately, sometimes I just need to download a part of the video like 10 seconds of a 3 hour video and here is how I see I can do it.

  Step 1 : Get the URL of the mp4 file from youtube-dl.

  youtube-dl -g -f "[ext=mp4]" https://www.youtube.com/watch?v=qOZ1u9VpoMk

  This returns $url : the full URL of mp4 file on server.

  Step 2 : Download part of the video using curl

  curl -r $startBytes-$endBytes $url

  But how to calculate $startBytes and $endBytes. What is the formula for that ?

  P.S I was thinking could be something as simple but this isn’t it..

  $startBytes = (total_size_of_video / total_length_of_video_secs) * start_seconds

  P.P.S. When I play the mp4 video in Chrome and use the scrub bar to jump around in the video, Chrome too send the Range header to the same URL (as I can see in fiddler)

• Generate individual HLS-compatible .ts segments on-demand by downloading as little bytes as possible from a remote input file

  27 janvier 2017, par Romain Cointepas

  I’m trying to generate individual HLS-compatible .ts segments on-demand by downloading/reading as little bytes as possible from a remote input file (hosted on a server supporting byte-ranges requests).

  One of the application for this would be to be able to transcode and play on Apple TV (via Airplay) a remote file that is not Airplay compatible, without having to download the entire file first.

  I am generating the playlist myself, and I have access to the ffprobe results for the remote file (that gives video duration, etc.).

  I have something working that plays via Airplay but with small video and audio glitches between each segments when I use the following command to generate each segment :

  ffmpeg -ss 60 -t 6 -i http://s3.amazonaws.com/misc-12345/avicii.vob -f mpegts -map 0:v:0 -map 0:a:0 -c:v libx264 -bsf:v h264_mp4toannexb -force_key_frames "expr:gte(t,n_forced*6)" -forced-idr 1 -pix_fmt yuv420p -colorspace bt709 -c:a aac -async 1 -preset ultrafast pipe:1

  Note : above command is for segment 11.ts, and in the m3u8 playlist I advertise each segment duration as 6 seconds.

  Here is a Youtube video showing the audio/video glitches between segments :
  https://www.youtube.com/watch?v=0vMwgbSfsu0

  The segment or hls modules of ffmpeg can’t be used because they both generate all the segments at once.

  I’ve been struggling on this for some days now and I would really appreciate some help !