Xvid bitrate vs. h264 bitrate

[EijiShinjo]

I convert 720p h264 videos to 720p Xvid in a AVI container so they play smoothly on my Xbox via XBMC.

For example, if there is a 720p h264 movie with a bitrate of 4000kbps, do I select a bitrate of 4000kbps for the Xvid encode or is a higher bitrate needed for Xvid to closely match the original 4000kbps of the h264 encode?

Also, does the bitrate-based mode in MediaCoder encode with a constant bitrate? I find it encodes nearly twice as fast as Two-pass mode but with pretty much the same file sizes. Picture quality also looks the same too.

Thanks.

[chornobyl]

you may use msu-vqmt to measure precise quality loss in xvid compering to h264, but note that all psy related stuff should be turned off http://compression.ru/video/quality_measure/vqmt_download_en.html

[DJ Bobo]

Let me be clear here: recompressing always harms quality no matter how much you bump up the bitrate!
So to keep as much as possible from the original quality, set the bitrate as high as you can!
Since you don't seem to care about file size, ideally encode in quantizer mode, with quantizer=2, that is the best quality you can achieve, and is of course faster than 2-pass, since it is 1-pass only.

[EijiShinjo]

Well, file size is an issue because the Xbox FatX filesystem doesn't allow file sizes above 4GB so the size has to be less than that.

MediaCoder doesn't have an option to set the Xvid quantitizer but it does have a quality based mode setting which you can set the value from between 0-100.

Which figures in this quality based modes would equal quantitizer 2 and 4?

[DJ Bobo]

I don't work with MediaCoder, sorry, but I'd guess that quality based 100 is equivalent to quantizer 2. You can check by encoding a one minute clip, one time with MediaCoder and one time in VirtualDub (which gives you access to the inner parameters of XviD) and compare the file size.

For the file size problem, you have 2 solutions:
* You split the output in 2 or 3 parts after encoding
or
* You use the 2-pass mode and make sure you get as close as possible to 4GB to maximize the quality.