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• encoding a video for looping ?

  24 janvier 2013, par bennettk

  This is somewhat related to Looping a video with AVFoundation AVPlayer but that question is answered. What I'm trying to achieve is seamless looping using an AVPlayer. There is a noticeable stutter between loops using h264-encoded videos* that has gotten worse for some reason with the update to iOS 5. Could this have something to do with the way the videos are encoded rather than the AVPlayer ? The looping is triggered by a playerItemDidReachEnd notification as described in the link above.

  Thanks.

  * here's the ffmpeg command we're using to encode the videos, if that helps :

  ffmpeg -i -y -sameq -vcodec libx264 -vpre hq -crf 20 -an

  (yes, the files don't have sound (yet) so the -an is intentional.)

• Node.js asynchronous video conversion slow

  9 décembre 2016, par lukstei

  I wrote a little website/service, which can download a video from a website (currently Youtube) and converts it on the fly to an mp3 file and sends this file back as the response.

  For example, you when you request http://localhost:8000/v=http ://www.youtube.com/watch?v=HhoewflkQu0, then it will download this video and response the audio layer encoded in MP3.

  This all works very well, my problem is that this is very slow and I can’t figure out why.

  ---

  Simplified the script behaves like this :

  Download the video and write it to the stdin of ffmpeg, and the stdout goes to the response.
  Video (MP4, FLV) -> FFMPEG -> MP3

  I used curl to figure out how fast the script is :

  $ curl http://localhost:8000/v=http://www.youtube.com/watch?v=HhoewflkQu0

  I get only about 5-10k.

  So why is this so slow ?

  1. The server, from which I am downloading the video is slow.
  2. The conversion is slow (because of a slow CPU).
  3. The data transfer between node.js -> FFMPEG is slow.

  I tried to download the video in a normal download manager, and i got about 320k, which is my normal download speed, so the first point isn’t the bottleneck.

  To point 2 and 3, I tried to write a local file to the stdin, and I got about 600k so that isn’t it either.

  So why is my script so slow, and what can I do to make it faster ?

  https://gist.github.com/1304637

  Thanks in advance.

• ffmpeg h.264 video plays in Safari but not in Chrome

  6 mars 2016, par ensnare

  I’m using ffmpeg to encode a .MOV raw video into a compressed H.264 video for display on an html5 website. I’m using the below string to encode the video :

  ffmpeg -y \
  
  -i in.mov
  
  -b 3500k -bt 4000k \
  
  -acodec libfaac -ac 2 -ar 48000 -ab 192k \
  
  -vcodec libx264 -vpre ultrafast -vpre baseline \
  
  out.mp4

  The resulting video looks great and plays fine in Safari, but Chrome can’t recognize it. Any ideas ?

  Thanks.