Filesize prediction in Gknot for DivX 5 is off

[dragoman]

Hi,

I encoded Independence Day Special Edition twice last night, once using DivX 5.0 and another using DivX 5.0 Pro. The results of these encodes are in other posts here in the forum.

The point of this thread is to point out the filesize prediction in Gknot for DivX 4.0 will not work with DivX 5.0

For example...

I wanted to make a ~1 GB file to mux with the ac3 sound. Gknot gave me a bitrate of 617kb/s for this filesize. This seemed small so I went ahead with the arbitrary bitrate of 1000kb/s.

Glad I did. Filesizes came out to 1075MB using DivX 5.0, and 997MB using DivX 5.0 Pro with b-frames, same bitrate both times.

The same bitrate fed into Gknot's bitrate calculator (with no audio of couse) gives you a filesize of 1420MB, or 1.42 GB.

If this seems high keep in mind we are talking about a 2hr, 35 min movie here...:) If you want to test it yourself the # of frames is 220865, or 9212 seconds.

Seems DivX 5.0 and 5.0 Pro live up to the claims of smaller file size.

Just thought I would point this out....do NOT rely on DivX 4 bitrate calculators when encoding DivX 5.0...!

dragoman

[khp]

This is pretty bad !!!

It should never be left to a bitrate calculator to predict how much the bitrate setting will differ from the actual average bitrate in the output file. Because any such difference will most likely fluctuate greatly from one movie to another.

It should alway be up to the codec, to achive an average bitrate that is as close as possible to the desired bitrate. Otherwise filesize prediction will become next to impossible.

I doubt "Divx5.0 bitrate calculators" will be able to fix this, it must be fixed in the codec.