XviD, BVOP, warp points... I Need some help

[Zenitram]

When I read for DivX hardware player information, I see sometimes
"GMC in DivX is 1 warp point, GMC in XviD is 3 warp points, hardware players does not support GMC with 3 warp points".

OK, but :
* if I use MPEG4 Modifier or GSpot on a file know to have 3 warp point, Both say "no GMC".
* MPEG4 Modifier says :
Packed bitstream: No
QPel: No
GMC: No
Interlaced: No
Aspect ratio: Square pixels
Quant type: H.263

I-VOPs: 38 (3,45%)
P-VOPs: 901 (81,69%)
B-VOPs: 0 (0,00%)
S-VOPs: 65 (5,89%)
N-VOPs: 99 (8,98%)

Warp points used:
1: 89,23%
2: 6,15%
3: 4,62%

--> I don't understand ; there are warp point, but no GMC.
What is unsupported on hardware players? 3 "warp point" or GMC? what is the link between GMC and warp points?

(My goal : to be able to easily detect if an hardware player can read a file)

[SeeMoreDigital]

Currently, only 1-warp-point GMC is supported in stand-alone players, which as far as I know is only offered by DivX. Even so, it's arguable that DivX's 1-warp-point GMC implementation actually does anything to improve compressibility.

XviD and NeroDigital offer 3-warp-point GMC, which is not (at the present time) supported in stand-alone players.

When generating encodes with GMC (whether it be 1-warp-point or 3-warp-point) it's advisable that you crop away any black mattes.... Because leaving such large amounts of "static" black may hamper the way GMC works due to their lack of motion.

I can't answer why MPEG Modifier is not able to correctly identify GMC (aka: S-VOP's), especially when the S-VOP's are listed separately.... Maybe Moitah can clarify!


Either-way, my advice to anybody is: Do not to generate encodes with GMC as it's more bother than it's worth ;)


Cheers

[Zenitram]

OK, Thanks, I understand better.
In my file, the sprite_enable tag (in the VOL) is set to "sprite not used", not to "GMC", this is maybe why MPEG Modifier does not show it.
But there are S-VOP in this file... Surprising.
I will not trust this tag to detect GMC.

[SeeMoreDigital]

Try these 3-warp-point GMC (http://www.one.seemoredigital.net/MPEG-4_Player_Test_Files/3-Warp-Point_GMC_Samples.7z) samples.

Please note: they have not been encoded to look good, they don't contain audio and they've been muxed into the MP4 container with 16:9 DAR signalling ;)


Cheers

[Zenitram]

Your 2 examples have the sprite_enable tag set.
My file is so surprising... It comes from divxtest CD v2 (http://www.divxtest.com).
If I understand, in all cases, I have to parse the whole file to detect if GMC has 1 or 3 warp points, to know if a hardware player can read it :(

[SeeMoreDigital]

My file is so surprising... It comes from divxtest CD v2 (http://www.divxtest.com).I guess you are referring to "VID-3G.avi"....

If so this is not a particularly good sample to "judge" warp-points because it switches between 0 -> 1 -> 3 warp-points in one continuous encode!

While interesting, you can't actually generate GMC encodes like this "in real life".... so it's a pretty pointless sample :eek:


If I understand, in all cases, I have to parse the whole file to detect if GMC has 1 or 3 warp points, to know if a hardware player can read it I don't think so... I think the info is written somewhere in the header.

That said, from what I remember NeroDigital generate 3-warp-point GMC encodes quite differently to XviD.


Cheers

[sysKin]

If so this is not a particularly good sample to "judge" warp-points because it switches between 0 -> 1 -> 3 warp-points in one continuous encode!

While interesting, you can't actually generate GMC encodes like this "in real life".... so it's a pretty pointless sample :eek:

Huh? Why? Did I misunderstand something?

Anyway, this clip could not have been done with XviD, because XviD will never use a single-warppoint GMC. Either p-vop, or 2 or 3 warppoints only.

[Zenitram]

I guess you are referring to "VID-3G.avi"....
You guess... Right! :-D
OK, this was done for tests, and "in real life", this is not possible, so I can trust the header to know if GMC is enable or not.

I don't think so... I think the info is written somewhere in the header.
I found for "GMC" tag (sprite_enable == “GMC” in the ISO specification), and I look more, the info about count of warping point should be in "no_of_sprite_warping_points" ;-).
But : possible values are :
Number of points warping function
0 Stationary
1 Translation
2,3 Affine
4 Perspective
I understand that DivX use Translation, Xvid Affine, is a codec use Perspective mode (4 warp points)?

That said, from what I remember NeroDigital generate 3-warp-point GMC encodes quite differently to XviD.
Do you meet a hardware player which read XviD 3 warp point GMC but not Nero 3 warp point GMC?

Anyway, this clip could not have been done with XviD, because XviD will never use a single-warppoint GMC. Either p-vop, or 2 or 3 warppoints only.
I look more on the file, and this file is in reality 3 files :
- XviD without GMC (this is why the GMC "tag" is not set in the header)
- DivX with GMC (1 warp point)
- XviD with GMC (3 warp points)
which have been "merged".

[SeeMoreDigital]

Do you meet a hardware player which read XviD 3 warp point GMC but not Nero 3 warp point GMC?Apparently Zoran's newest chip-set, the Vaddis 888 supports both 1-warp-point and 3-warp-points

You can read a little more about it here (http://forum.doom9.org/showthread.php?t=110273) ;)

Huh? Why? Did I misunderstand something?

Anyway, this clip could not have been done with XviD, because XviD will never use a single-warppoint GMC. Either p-vop, or 2 or 3 warppoints only.
I look more on the file, and this file is in reality 3 files :
- XviD without GMC (this is why the GMC "tag" is not set in the header)
- DivX with GMC (1 warp point)
- XviD with GMC (3 warp points)
which have been "merged".Indeed... this was what I thought.

In reality a sample encoded like this could crash your stand-alone player (as it did with my Zensonic Z500).


Cheers

[fight2win]

where to download xvid latest build?

[foxyshadis]

Er, same places you have been able to for ages?

http://ffdshow.faireal.net/mirror/XviD/
http://www.koepi.org/xvid.shtml

Use search!

[fight2win]

thanks foxy baby!