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Re: H264 to MPEG-2 - very different transcode times

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Daniel Low
Re: H264 to MPEG-2 - very different transcode times
on Sep 26, 2008 at 4:15:05 pm

Handbrake is a very efficient transcoder, it's actually great at producing very high quality pictures at low bit rates. It's designed to rip a 4GB movie and fit it into 650MB without any loss in quality.

What you have found by skipping through the Handbrake clip is that there are far greater distances between H.264's equivalent of I-frames. I-frames contain a full frame of information, all the other frames need to calculate themselves based on that I-frame.

So when compressor starts to process it, it has to look ahead at each frame and each time it lands on anything other than an i-frame it needs to calculate the result and this takes time. The greater the distance between i-frames the longer the calculation.

Look under the 'Options explained' (Frames) section here to see how complex this process can be
http://trac.handbrake.fr/wiki/x264Options

Combustion won't have anything like as complex an encoder and as such it's easier to read from.

If you converted both clips to an I-frame only format you'll find that they both transcode at the same rate.

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