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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.

• 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 !

• Merging .flv chunks from stream site

  4 décembre 2016, par Iztooi

  I’m trying to download a video from an alternative version of the Ustream site. This site is apparently used for a DRM protection, in fact you can’t watch this video without having access to it through a login from this site.
  The video system should be the same used by ustream (same links), that is calling different flv chunks every x seconds and merging them into the stream (similar to an rtmp service, but it doesn’t use this protocol).

  I managed to download every .flv chunks composing this video, but i had issues on merging them into a single file. First of all these flvs files have some audio/video lags/problems, but since there is no other way to download this video i’m not complaining about lags.

  The real issue is that every flv file has an additive increase on the duration, despite having a normal size. Video duration is about 6 seconds, so the first chunk is 6 seconds long, the second chunk is 12 seconds long, although only the first 6 are visible (the remaining 6 are "corrupted"). If i try to merge (with ffmpeg or any video-joining software) all these files (about 600-700, for a total duration of 1 hour and 15 minutes) only the first two sections are visible, then I cannot see anything. (Being more clear, if i try to merge the first 2 chunks, file is 18 seconds long and i can see the first 12 ; if i try to merge the first 3 chunks, file is 36 seconds long and i can still only see the first 12 seconds.)

  Anyone has any idea ?