• Compression Techniques

  exploring maximum and minimum bitrates

  Posted by Michael Rampe on March 17, 2010 at 9:46 am

  If you type -b 10k (stupidly low) into the bitrate for a large movie, it will always be higher which sets a minimum bitrate for that image size. The codec needs that minimum bitrate to satisfactorily draw a picture with its most basic level of averaging.
  ffmpeg -i fluid.mov -vpre libx264-hq -vcodec libx264 -b 10k 10kout.mov
  = 150 kbps at 1024X576

  Also, on the flipside, if you type -b 100000k, you will get a lower bitrate. (eg. 720×576 usually peaks at about 10-12 Mbps for mpeg2)
  The codec has done every fancy thing it has up its sleeve and has nothing left to do so it needs no more bits.
  ffmpeg -i fluid.mov -vpre libx264-hq -vcodec libx264 -b 100000k 100000kout.mov
  = 9340 kbps at 1024X576

  From the testing I have done with ffmpeg, it seems any video has a minimum and maximum bitrate based on numerous factors. (content type, movement, frame size, frame rate etc.)

  Michael Rampe replied 16 years, 4 months ago 1 Member · 0 Replies
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