dx50 b-vop...

[nanga parbat]

good day!

i know it is propably covered somewhere, but my search just returned too much and it could not really answer my question...

so: this option, has it, besides making the stream compatible to dx50, any other effect?
i mean, there could be some ppl around wanting to decode a particular video as dx50, but i normally do not do this.

i am asking, because in the settings thread it is only mentioned to check this option - would it be right, if there was said sth like 'check this option if you want to play your video with dx50-decoder, otherwise you may keep it unchecked' ?

thanks for your effort!
nanga

[Selur]

any other effect?
"DX50-BVOP compatibility" aka. "closed GOP":
When encoding MPEG video, a GOP which uses no referenced picture from the previous GOP at the current GOP boundary, is called Closed GOP. On the other hand, a GOP which uses referenced pictures included in the immediately previous GOP, is called Open GOP.
(GOP = group of pictures)

Also read this thread:
http://forum.doom9.org/showthread.php?s=&threadid=56190

Cu Selur

[unmei]

a GOP extends from I frame till right before the next one ?

If so this equals closed GOP = no B-frame just before an I-frame which leads to "DX50-BVOP compatibility" = "can cut stream before an I-frame without making any B-frames screw by loosing their future reference frame"

..or was my initial assumption on GOPs wrong ?

[Selur]

no afaik that's how it is ;)

[sysKin]

Yes guys, you are all correct.

There is yet another thing that is worth mentioning. XviD tries to put I-frames as frames beginning a new scene. If a b-frame, which still belongs to previews scene, would have such i-frame as reference, it would not use it, because the i-frame looks completely different.

As b-frames are designed to use two references, if one is useless, the total compression efficiency drops.

As a result, "Closed GOV" (I think it's GOV, as Group Of Video objects... I might be wrong) gives better compression than open-GOV.

Radek

[mf]

Originally posted by sysKin
As a result, "Closed GOV" (I think it's GOV, as Group Of Video objects... I might be wrong) gives better compression than open-GOV.

Radek
According to dev-api-4 GUI it's GOP :p.

[sysKin]

Originally posted by mf
According to dev-api-4 GUI it's GOP :p.
According to dev-api-4 GUI it's GOV :p :p

But It's GOP in ffvfw's gui.

:confused:

[mf]

oro :eek:
That's weird - my api4 build (outdated, yes) said GOP. :confused:

[nanga parbat]

well, thank you all for the replies. i think i got the (group of) picture ;)

in essence: it's not just about playback incompatibility, open gop also will make cutting problematic and may introduce a drop in compressibility at scenechanges.

right?

btw. will cutting an open gop stream result in a loss of the whole sequence (pbbpbb or so) that came before the keyframe that has been cut at? i got that impression...

bye, nanga

[sysKin]

OK, it's GOP all over google, so it probably is a damn GOP - at least in mpeg-1 and mpeg2 ;p.
However it does say GOV in xvid's sources too ;p ;p. Whatever.

Originally posted by nanga parbat
will cutting an open gop stream result in a loss of the whole sequence (pbbpbb or so) that came before the keyframe that has been cut at? i got that impression...Only last b-frames will be lost. In fact they will not be lost, but if you cut, they would be copied to the *next* scene (because in coding order, they are *after* i-frame) and will not be decodable, but will still eat up some space.

[Selur]

just for the confused ones:

VS = visual object sequence
VO = video object
VOL = video object layer
VOP = video object plane
GOV = group of vops (vop = video object plane)


afaik in mpeg4 you speak of B/I/P-vop instead of B/I/P-frame, so GOV should be the mpeg4-term for the 'normal mpeg' term GOP. :)

Cu Selur

[Barker]

Nice thread, I learned a lot from this, thanks to all that have contributed thus far. Maybe this should be consolidated into one of the stickys? (Not just for XVID, but the definitions of the terms widely used) It might give people more of an idea of what GOP, GOV, VOB, VOL,etc.. mean.

Much respect goes out to all involved in the coding and testing of these codecs, we all appreciate it.

Thank You
Regards,
Barker

[superdump]

VOB is a typo I believe. It should be VOP.

[Barker]

Good call, can you tell I was CNTRL-C/CNTRL-V'ing it? :(

Hehe

Im retarded, also I was thinking VOB as in the DVD structure. Anyhow, nice observation.

Regards,
Barker

[Selur]

Yup, VOB was a typo, and yes it should have been VOP.
(edited it)

Sorry :D

[neoviper]

Back to the original topic.
You may want to disable this option when encoding credits separately as it saves some bits.
A very small save but still... :p