Xvid and MPEG-4

andy

Correct me if I am wrong, but AFAIK Xvid is an implementation of the MPEG-4 standards... right?

I have a couple of questions:

Right now (April 12, 2003), how compatible is Xvid with the standard? Are there any Xvid settings that can be adjusted to provide a 100% compatible stream, and others that will just nullify any compatibility?

How does Xvid compare with DivX, Apple and Microsoft's MPEG-4 encoders? I mean, compatibility wise, not quality wise.

I ask beacause it seems that MPEG-4 will actually start coming out on standalone players, but alongside it will be the WM9 codec. I am wondering if Xvid encodes I do now can be played on any standards-compliant player.

Thanks!

If you want to be sure of being 100% MPEG 4 compilant, don't use the MPEG 4 Advanced Simple Profile settings (GMC amp; QPEL).

I always use:

Motion precision=6
VHQ=1
Lumimasking amp; Chroma motion
B Frames (that now are fully compilant)
Chroma optimizer.

Nothing else.

Then put it into an MP4 container using lastest MP4IP and all is ok

err, bframes are also a MPEG 4 Advanced Simple Profile setting.

[edit] arg, got my not's mixed up

Originally posted by TheXung
err, bframes are also not a MPEG 4 Advanced Simple Profile setting.

AFAIK B-frames is part of the mpeg 4 advanced simple profile.

@LoKi128

You are talking about two different things here.
On the one hand the most XviD settings (I think all beside modulated quants) should be mpeg4 compliant. But it can be that some new implemented features break compatibility. Although I think that only happened twice so far it's the reason why the developed XviD versions are called unstable.  
On the other hand if you want to play your movies on one of those standalone players you can't use b-frames, q-pel and gmc because those features are advanced simple profile settings and I think the standalone players only support simple profile.

Regards
Assault

Assault is right - the only feature which is not mpeg4 compatible is modulated quant. Of course the version is called 'unstable' because we can't guarantee a thing

If you want to play XviDs on standalone players, just make sure that the profile you use is compatible with them. Qpel and GMC are not supported by any currently existing standalone as far as I know.
If any player would say that it's able to decode 'divx5 GMC' it doesn't mean that it's able to decode XviD GMC, becuase XviD's GMC is 2-point (3-point in near future, we hope), while divx5's one is 1-point only.

Radek

Originally posted by Assault
On the other hand if you want to play your movies on one of those standalone players you can't use b-frames, q-pel and gmc because those features are advanced simple profile settings and I think the standalone players only support simple profile.

I think that B-Frames are supported by Standalones. Try to use portable, home theatre or High defiinition profile of DivX 5.03, you can enable them (but you can't use GMC and QPEL). I think it will be the same for Xvid too.

AFAIK it's safe to use all features but GMC, QPEL and modulation.

Thanks for all your replies!

BTW, for people who don't know what the different quot;profilesquot; are etc, here is the MPEG-4 Standard document.

Anyway, it seems to me that none of the current hardware players actually supports the MPEG-4 standard. Well, they all support the Simple Profile, but that is just like the bare minimum. So they are really just DivX players, with a little MPEG4 badge that dosnt mean much.

Question is... how will the machines of the future behave? For example, as sysKin said, XviD has a 2-point GMC. Is this part of the standard? Will a full implementation of MPEG-4 (a daunting task, after reading that website above) know how to handle different versions of GMC?

Anyway, looking around I also found Osmo4 which supposedly is the most complete MPEG-4 player right now. And it uses the XviD libraries for the video portion. It can also decode 2D streams. Haven't installed it yet tho.

I guess as a parting question... are the XviD developers shooting for MP4 compliance? Or will they sacrifice it to get better quality at a smaller bitrate?

Originally posted by LoKi128
For example, as sysKin said, XviD has a 2-point GMC. Is this part of the standard? Will a full implementation of MPEG-4 (a daunting task, after reading that website above) know how to handle different versions of GMC?

Yes it's part of the standard. Let's just hope that hardware developers won't say quot;we don't have to implement the real standard, all we need to implement is DivX5 and we'll sell everythingquot;. It wouldn't be nice...are the XviD developers shooting for MP4 compliance?

Definitely yes.

Or will they sacrifice it to get better quality at a smaller bitrate?

I'd love to do that  If anyone will ever do that, it won't be XviD anymore and he won't even _pretend_ to be mpeg4 compatible. So the answer for XviD is: no, compatibility will not be sacrificed.

Radek

A small thing out of topic (sorry moderators   )

If I turn off DIVX B-VOP compatibility, the output file is still MPEG4 full compilant (so also if the B frame takes for future reference an I frame, right?)