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Old 5th January 2005, 13:11   #1  |  Link
SeeMoreDigital
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GMC: observations... and now discussions!

Yesterday, a fellow Doom9 forum member going by the name of Skuto, made (what I think is) an interesting GMC observation, when playing back NeroDigital encodes via his NeroDigital certified stand-alone player - the Siemssen SCO 5000!

As some of you know NeroDigital generates Mpeg4 encodes with 3 warp-point GMC (the same as XviD) and as far as we know, there are currently no players supporting this implementation... Not even NeroDigital certified stand-alone players.

Anyway, when Skuto fed the player with such an encode, it played So during a moment of experimental madness I decided to see whether my Sigma Xcard would play such encodes too - And would you believe it, it did

So, this begs the question. How many other stand-alones can play NeroDigital encodes with 3 warp-point GMC?

Obviously, you'll need to de-mux Nero's Mpeg4 stream from out of the the .MP4 container to .AVI (and maybe even rename the 4CC code to XviD or NDIG). And, if you want audio, you'll have to convert Nero's AAC stream to MP3. But remember... it's just an experiment.


Now for all those who don't believe that Nero digital streams contain 3WP GMC. Here's what Mpeg4 Modifier had to say about it: -



And here is what Mpeg4 Modifier said about XviD streams encoded with 3WP GMC (which incidentally do not play with my Xcard): -




Could XviD's GMC implementation be broken. Could NeroDigital's. What can anybody make of this?


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Last edited by SeeMoreDigital; 15th February 2005 at 11:20.
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Old 5th January 2005, 13:24   #2  |  Link
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GMC in Nero's MPEG-4 is 3-Warppoints.

However, the player will play it correctly till GMC is indeed used, which may not often happen. Did you check with FFDShow that GMC was indeed used on at least a frame in the clip ?
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Old 5th January 2005, 13:44   #3  |  Link
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Quote:
Originally posted by Manao
Did you check with FFDShow that GMC was indeed used on at least a frame in the clip ?
I'm curious, what relevance would this have for a "hardware player" user?

And how can XviD's 3WP implementation work so differently to NeroDigital's?


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Old 5th January 2005, 15:05   #4  |  Link
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Quote:
I'm curious, what relevance would this have for a "hardware player" user?
GMC is not used throughout the movie, only on specific frames where it makes sense. I don't know how the GMC and warp point signalling works, but I suppose it could be signalled without the feature actually being used. And if GMC is not actually used in a clip, the clip should play on any device that cannot handle 3pt GMC since it never has to decode such frames.
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Old 5th January 2005, 15:18   #5  |  Link
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Thanks Doom9,

This raise another question. If GMC does work in this way, then "might" it be possible to have a tool that can switch off or remove the GMC signalling all together?

Such an implementation might prove handy for people who've generated Mpeg4 encodes with (3WP) GMC but who have stand-alones that can't play them!


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Old 5th January 2005, 15:25   #6  |  Link
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as i understand it, frames where GMC is used are called "S-VOPS". so if you trust MPEG4-Modifier, the get used a lot in both clips from SMD (47% and 19% of all frames). so if they can be played correctly (with no quality issues) it looks like 3WP-GMC is indeed supported.

@SMD: did you try to change the FourCC and the userdata string of the xvid clip to the same as the nero-digital clip?
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Old 5th January 2005, 15:41   #7  |  Link
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Quote:
Originally posted by thana
SMD: did you try to change the FourCC and the userdata string of the xvid clip to the same as the nero-digital clip?
As a matter of fact I did... There was no change!

I'm glad you picked up on the fact that MPEG Modifier does indeed show more S-VOP's in the NeroDigital clip than in the XviD clip.


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Old 5th January 2005, 16:24   #8  |  Link
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Could be because XviD doesn't use GMC if only 1 reference is found and Nero does. No idea if that is the case but it would explain why there are more S-VOP's.

For instance my MTK based player from what I remember plays GMC'ed XviD files fine until it (presumably) hits a 3 warp point S-VOP where decoding gets "stuck". Not sure what effect there is with 2 warp point S-VOP's.
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Old 5th January 2005, 17:12   #9  |  Link
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jep what celtic_druid says is correct at least for the MediaTek Chip and Firmware it will bork on 3 Warppoint GMC frames (S-Vops) often they are used for a long duration, you'll have a slideshow then :P
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Old 5th January 2005, 17:35   #10  |  Link
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Quote:
Originally posted by CruNcher
jep what celtic_druid says is correct at least for the MediaTek Chip and Firmware it will bork on 3 Warppoint GMC frames (S-Vops) often they are used for a long duration, you'll have a slideshow then :P
Yes... but have you or celtic_druid tried an "NeroDigital" Mpeg4 encode with 3 warp-point GMC?

EDIT: Like this one!


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Old 6th January 2005, 16:08   #11  |  Link
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But can you tell whether it's really using 3 warp points anywhere, or whether the stream reports 3 warp points while only 1 or 2 are actually used? I recall reading that NeroDigital only implemented 2 warp points, though that was quite a while ago.
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Old 6th January 2005, 16:39   #12  |  Link
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Quote:
Originally posted by Sergei_Esenin
I recall reading that NeroDigital only implemented 2 warp points, though that was quite a while ago.
The NeroDigital ASP encoder has always encoded 3-warping points.

There is an optimization reducing the number of warpoing points if some are not necessary.
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Old 6th January 2005, 18:54   #13  |  Link
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Anybody had chance to try my "NeroDigital" Mpeg4 3WP GMC .AVI encode, on their stand-alone player yet?

If not, it's still here.


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Old 6th January 2005, 23:05   #14  |  Link
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If it only was possible to find out how many warppoints actually are used in the bitstream! Anyone?
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Old 7th January 2005, 15:50   #15  |  Link
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I've just tried SMD, and my standalone doesn't want to play it at all, so it's not much help to you
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Old 7th January 2005, 15:52   #16  |  Link
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Quote:
Originally posted by niamh
I've just tried SMD, and my standalone doesn't want to play it at all, so it's not much help to you
What make/model of stand-alone do you have?


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Old 8th January 2005, 19:20   #17  |  Link
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Itīs a non-brand... anyway, silly me forgot to change the 4cc to xvid .
It now plays flawlessly, motionwise.( Xvid gmc gives me the usual slideshow.)
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Old 14th February 2005, 12:14   #18  |  Link
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GMC Removal

Quote:
Originally posted by SeeMoreDigital
Thanks Doom9,

This raise another question. If GMC does work in this way, then "might" it be possible to have a tool that can switch off or remove the GMC signalling all together?

Cheers
That's what I am after a tool for removal. In the meatime can anyone point me to an FAQ or tutorial on GMC removal through re-encoding? For some reason my re-ecodes always end up 33% bigger than the source when I remove GMC?! Also whats the best tool for this? (only tried virtualdubmod)

Thanks,

Laffer.
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Old 14th February 2005, 12:33   #19  |  Link
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ok bobololo described what happened in the observation SMD described (3wp gmc playable on a player not handling 3wp gmc) here:
http://forum.doom9.org/showthread.ph...0&pagenumber=2

to make it short: the clip only signals 3wps, but doesnt use them
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Old 14th February 2005, 13:56   #20  |  Link
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Quote:
Originally posted by bond
ok bobololo described what happened in the observation SMD described (3wp gmc playable on a player not handling 3wp gmc) here:
http://forum.doom9.org/showthread.ph...0&pagenumber=2

to make it short: the clip only signals 3wps, but doesnt use them
Jeez... me and my brain... I forgot I had started this thread

Yes, bobololo post revealed some very interesting information about NeroDigital's approach toward their 3WP GMC implementation.

I wonder if the XviD guys could provide information about their approach too?


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