GMC quality question

[Tommy Carrot]

The question is plain and simple:

Do you experienced any quality improvement with GMC swiched on?

/Because i've thoroughtly tested both xvid and divx5, and in neither cases did i see any improvement. The image is different, but not better or more detailed./

[Teegedeck]

The picture is not supposed to be better or even different. GMC saves bitrate - but ONLY on scenes with zooms (the saving makes for about 1-2%).

And don't use GMC together with VHQ - their concepts kind of collide and in the effect, GMC doesn't save anything if combined with VHQ.

As for DivX5: If they haven't improved GMC from the 5.0.2 version, their GMC doesn't help anything, it's just there so they could say it's there...

[Big_Berny]

Sorry, bu I have to correct you! GMC of DivX 5.02 saves a little bit space! But not in 5.03! I posted it somewhere in the DivX-part of this forum.

Big_Berny

Originally posted by Teegedeck
The picture is not supposed to be better or even different. GMC saves bitrate - but ONLY on scenes with zooms (the saving makes for about 1-2%).

And don't use GMC together with VHQ - their concepts kind of collide and in the effect, GMC doesn't save anything if combined with VHQ.

As for DivX5: If they haven't improved GMC from the 5.0.2 version, their GMC doesn't help anything, it's just there so they could say it's there...

[Teegedeck]

Yes, I posted in that thread, too.
Hi. :)

So; they've messed up GMC in the 0.3 version, ey? Now, anything they haven't messed up in 5.0.3?

[sam_b]

Their licensing :p

[Sirber]

lol

a good one :D

[Tommy Carrot]

Originally posted by Teegedeck
The picture is not supposed to be better or even different. GMC saves bitrate - but ONLY on scenes with zooms (the saving makes for about 1-2%).

And don't use GMC together with VHQ - their concepts kind of collide and in the effect, GMC doesn't save anything if combined with VHQ.

As for DivX5: If they haven't improved GMC from the 5.0.2 version, their GMC doesn't help anything, it's just there so they could say it's there...

I know GMC is intended to save bitrate. But for 2-pass, the same sized encoding doesn't provide better result at all, which is understandable, if the bitrate saving is so tiny. I though, apart from that, it can enhance somehow the quality, better pan handling, etc. This is why i'm asked: is using GMC makes sense?

/BTW, i don't like VHQ. It doesn't behave well with qpel./

[sam_b]

AFAIK xvid's GMC deliberately does not act on pans, as the m-block vectors can handle translations fine. I think all it does is reduce the amount of DCT data needed to describe a movement, as a rotation or zoom will only approximate a translation as seen by each individual block. I would have thought it would improve the picture *slightly* for clean movements.

I think that GMC is still predominantly a proof-of-concept, even if it is a very good one. syskin may able to tell you what savings are expected when finished.

Don't hold me to any of this BTW. One of the developers should be able to tell you more concretely.

[tangent]

Originally posted by Tommy Carrot
I know GMC is intended to save bitrate. But for 2-pass, the same sized encoding doesn't provide better result at all, which is understandable, if the bitrate saving is so tiny. I though, apart from that, it can enhance somehow the quality, better pan handling, etc. This is why i'm asked: is using GMC makes sense?

/BTW, i don't like VHQ. It doesn't behave well with qpel./

GMC increase quality in 2-pass by reducing the average quantiser and maintaining the same filesize. Bits saved using the same quantiser and GMC for a few frame would mean bits used to improve other frames.