Block Artifacts

[KidsonDj]

Hello, I am getting blocky artifacts in the dark, stationary areas of movies I encode (using xvid or normal mpeg-4). I have looked around the net and have become very confused, some say this is caused by b-frames, others blame Quarter pixel motion estamation and others still say its the hardwares fault (modded xbox) not upscaling the image well. Any clarification you guys can provide me would be great.
Thanks,
Kidsondj

[caozinho]

More infos would be helpful.
Source material, resolution & data rate of the encoded material, etc.
The statement about the Qpel ME causing block artifacts is completely rubbish.

[KidsonDj]

Cool: I'm encoding Video_TS (PAL) at like 1663Kb/s with a size of 832x352. I also have "high quality", 4 motions vectors, 2 pass encoding, trellis quantization, qpel and b-frames enabled and quantizer of 2-13.

I didn't think qpel would be causing it but someone said it might on another forum.
Thanks

[caozinho]

Why are you upscaling the source material? The Videostream within the TS folder only has a max. resolution of 720x576 when using AR 4:3. It seems you want to do an AR of 2.35:1, but your calculation depends on square pixels. Adding 112 dots in the vertical resolution doesn´t make any sense and could be one reason causing the artifacts.
I don´t know the specs of the media player for the XBOX. Is mplayer source code used for this? Maybe the used code has problems interpreting codec specific feautures. But other people having a XBOX at their hands should know more about this.

Cheers

[KidsonDj]

Sorry, those figures were just an estimate as I didn't have the source material at the computer I was at (that would be very strange to upscale it) so the resolution is actually 656x368 with a 1363kb/s bit rate, sorry for the confusion. Anyway, mplayer is the source code used for my xbox, maybe thats the problem.

[Case]

656x368 at 1363 kbit/s should be enough for NTSC film (23.976 fps) or PAL (25 fps) but maybe not enough for NTSC (29.97 fps), with a recommended (*) 1625 kbit/s mpeg-4 video bitrate for that frame size. If your bitrate is too low, that might give block artifacts.

(*) ffmpegX calculated ‘best’ bitrate.