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• FFMPEG ignores bitrate

  24 avril 2016, par Kevin Brydon

  I am new to video encoding so bear with me.

  I am using FFMPEG. I have an mp4 file which is 640 x 350 with an average bitrate of around 2000kb (I think) and a filesize of 80Mb. I want to convert this to an ogv file with a much lower bit rate (128kb) but the same width and height. I am using the following command...

  ffmpeg -i input.mp4 -b:v 128k output.ogv

  ... but FFMPEG seems to ignore my bitrate option and outputs a file with a bitrate of around 600kb and a filesize of around 3Mb.

  I can do this using FFMPEG2THEORA using the following command ...

  ffmpeg2theora -V 128 input.mp4 -o output.ogv

  ...but I was wondering if it was possible using FFMPEG.

  Any ideas ?

  Edit

  mark4o solved my problem. It turns out that the default audio codec was bumping up the filesize. Changing it to libvorbis has reduced the filesize dramatically. Final command looks like

  ffmpeg -i input.mp4 -b:v 128k -b:a 128k -codec:a libvorbis output128.ogv

  • -i = input file
  • -b:v = the bitrate of the video stream
  • -b:a = the bitrate of the audio stream
  • -codec:a = override the default audio codec

• FFMPEG : preset not found in Windows Vista

  12 juin 2012, par StackOverflowNewbie

  I download FFMPEG from http://www.videohelp.com/tools/ffmpeg#download and saved it in my c :\program files\ffmpeg (Windows Vista). My Path's first 2 entries are :

  c:\program files\ffmpeg\bin;c:\program files\ffmpeg\presets;

  I found the following command on the net (http://paulrouget.com/e/converttohtml5video/)

  ffmpeg -i input.avi -acodec libvorbis -ab 96k -vcodec libx264 -vpre main -level 21 -refs 2 -b 345k -bt 345k -threads 0 -s 320x240 output.mp4

  When I run this on command line, I get the following error :

  File for preset main not found

  Any ideas what might be wrong ?

• detecting a timeout in ffmpeg

  19 mai 2015, par Sean

  I am writing some software that uses ffmpeg extensively and it is multi threaded, with multiple class instances.

  If the network connection drops out ffmpeg hangs on reading. I found a method to assign a callback that ffmpeg fires periodically to check if it should abort or not :

  static int interrupt_cb(void *ctx) 
  
  { 
  
  
  
  // do something 
  
      return 0;
  
  } 
  
  
  
  static const libffmpeg::AVIOInterruptCB int_cb = { interrupt_cb, NULL }; 

  ...

  AVFormatContext* formatContext = libffmpeg::avformat_alloc_context( );
  
  formatContext->interrupt_callback = int_cb; 
  
  if ( libffmpeg::avformat_open_input( &formatContext, fileName, NULL, NULL ) !=0 ) {...}

  This is all fine but nowhere on the web can i find what *ctx contains and how to determine whether the callback should return 1 or 0. I can’t assign a static "abort" flag as the class has many instances. I also can’t debug the code as for some reason visual studio refuses to set a breakpoint on the return 0 ; line, claiming no executable code is associated with the location. Any ideas ?