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• ffmpeg problem in ubuntu (libavcodec.so)

  7 décembre 2016, par lyuba

  I run Ubuntu and try to use the ffmpeg wrapper in Java from here :
  http://code.google.com/p/javacv/

  It seems to work fine on other systems, but in Ubuntu the project crashes
  with the following mistake :
  Exception in thread "main" java.lang.UnsatisfiedLinkError : Error looking up
  function ’avcodec_decode_video2’ : /usr/lib/i686/cmov/libavcodec.so :
  undefined symbol : avcodec_decode_video2

  ffmpeg is working great from the command line, though.

  JavaCV author recommended me to check this link :
  http://linux-tipps.blogspot.com/2009/05/pretending-package-is-installed-by.html

  Probably I’m doing something wrong, but it cannot reinstall libavcodec51
  like this.

  So the questions are :
  1. Is those solution above a good one so I should bring it to success
  somehow ?
  2. What are the other ways to solve the problem ?

  Thank you for your suggestions in advance !

• Why is one ffmpeg webm dash stream much larger than the others ?

  5 janvier 2017, par ranvel

  Over the summer, I worked on putting together a script which took a x264 video/mp3 stream and broke it up into the different streams so that it would work via MSE-DASH. (Based heavily on the instructions on the webmproject.org website) Those same scripts have ceased to work, turning a 6GB video into several 25 Gb videos. I kept up with updates of ffmpeg and so I don’t know when it stopped working, but I am guessing it was due to the way that their DASH Webm implementation was updated.

  I found new method which works better, but still has a major problem with one stream. I was hoping someone could explain how this encoding works so that I could understand the underlying cause.

  #!/bin/bash
  
  COMMON_OPTS="-map 0:0 -an -threads 11 -cpu-used 4 -cmp chroma"
  
  WEBM_OPTS="-f webm -c:v vp9 -keyint_min 50 -g 50 -dash 1"
  
  
  
  ffmpeg -i $1 -vn -acodec libvorbis -ab 128k audio.webm &
  
  ffmpeg -i $1 $COMMON_OPTS $WEBM_OPTS -b:v 500k -vf scale=1280:720 -y vid-500k.webm &
  
  ffmpeg -i $1 $COMMON_OPTS $WEBM_OPTS -b:v 700k -vf scale=1280:720 -y vid-700k.webm & 
  
  ffmpeg -i $1 $COMMON_OPTS $WEBM_OPTS -b:v 1000k -vf scale=1280:720 -y vid-1000k.webm &
  
  ffmpeg -i $1 $COMMON_OPTS $WEBM_OPTS -b:v 1500k -vf scale=1280:720 -y vid-1500k.webm  

  The transcode is not yet complete, but you can see where this is headed :

  -rw-r--r--  1 user  staff    87M Jan  4 23:27 audio.webm
  
  -rw-r--r--  1 user  staff    27M Jan  4 23:42 vid-1000k.webm
  
  -rw-r--r--  1 user  staff   285M Jan  4 23:42 vid-1500k.webm
  
  -rw-r--r--  1 user  staff    15M Jan  4 23:42 vid-500k.webm
  
  -rw-r--r--  1 user  staff    20M Jan  4 23:42 vid-700k.webm

  The 1500k variant is disproportionately larger than the other streams.

  The other problem is that when I use a shorter video, lets say eight or nine minutes, the above configuration runs as expected and everything is perfect. I don’t know where the limit for this is since each test costs a lot of processing power and time, but if it’s less than ten minutes, it works and if its longer than an hour, it produces massive files.

• How to create videos with small file size but large resolution ?

  13 février 2017, par Gregory Magarshak

  Is there a programmatic way to create videos that capture, essentially, a powerpoint presentation, that would be not much larger than the audio + screenshots of the powerpoint itself ?

  I want to make software that produces videos with the full resolution of a powerpoint on a large screen, and with a person speaking over it and wvwn doodling. Kind of like "bcontext" software. And then I want to export videos for youtube and other places to be hosted. But I want them to be SMALL. So they can be downloaded by people with slow connections eg in India.

  What factors can affect video size and how can i take advantage of the relative "stillness" of most pixels at most times to make the compression preserve the full sharpness and yet take advantage of the lack of visual changes ? What software do you recommend ?