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• rails / streamio-ffmpeg - How to execute 2-pass encoding ?

  20 mars 2017, par R4ttlesnake

  I’m using streamio-ffmpeg to encode videos uploaded to my Rails application via ffmpeg. I want to encode the videos to .webm-format using the VP9 coding format and the VP9 Encoding Guide of the WebM Project recommends using 2-pass encoding. I managed to get the videos encoding via streamio-ffmpeg using 1-pass encoding, but I can’t figure out how to handle the 2-pass encoding.

  Here my setup so far :

  # create two tempfiles for the video and a still
  
  video = Tempfile.new(["video", ".webm"], binmode: true)
  
  still = Tempfile.new(["still", ".jpg"], binmode: true)
  
  
  
  # new FFMPEG
  
  movie = FFMPEG::Movie.new(original.path)
  
  
  
  # extract still from video
  
  movie.screenshot(still.path)
  
  
  
  # encode video
  
  options = %w(-c:v libvpx-vp9 -b:v 1000K -threads 8 -speed 4 -tile-columns 6 -frame-parallel 1 -auto-alt-ref 1 -lag-in-frames 25 -c:a libvorbis -b:a 64k -f webm)
  
  movie.transcode(video.path, options)

  The command to do a 2-pass encoding with ffmpeg would be :

  ffmpeg -i <source> -c:v libvpx-vp9 -pass 1 ... -f webm /dev/null
  
  ffmpeg -i <source> -c:v libvpx-vp9 -pass 2 ... -f output.webm
  
  </source></source>

  In particular, I don’t get how to pass the file of the first encoding step to the second step with streamio-ffmpeg. How would I apply these two steps to the syntax of movie.transcode(output, options) ?

  Thanks !

• avformat/matroskaenc : Simplify writing Void elements

  12 janvier 2020, par Andreas Rheinhardt

  avformat/matroskaenc : Simplify writing Void elements
  Reserving space in Matroska works by writing a Void element. And until
  
  now this worked as follows : The current position was recorded and the
  
  EBML ID as well as the length field written ; then the new position was
  
  recorded to know how much more to write. Afterwards the actual writing
  
  has been performed via ffio_fill().
  But it is unnecessary to explicitly use the positions (obtained via
  
  avio_tell()) to find out how much still needs to be written, because the
  
  length of the ID and the length field are known. So rewrite the function
  
  to no longer use them.
  Also, given that ffio_fill() uses an int parameter and given that no
  
  current caller (and no sane future caller) will want to reserve several
  
  GB of space, make the size parameter of put_ebml_void() itself an int.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• FFmpeg library in WPF

  20 avril 2022, par MikeTMG

  I am building a softwere that can decode and encode using Wpf and c#, and I want to do that using, FFmpeg libary. I saw the ffmpeg autogen warpper but I couldn't find any documantion for its function.
Can someone please find me one ? Or better, give me better warrper.

  



  I already tried FFMpegCore, its working but very slow. For Exaple it takes 20 seconds to decode a specific frame.(And i have monstruos computer)
If will be happy if ou could give me better warpper, or a guide for ffmpeg.autogen.
Thanks in advance.