About scene change detect

[FuFo]

Hi all
i'm new here but I'm an old Nandub's user.
So my question...: have Xvid an internal scene change detect or i must set it in Virtualdub preferences?

I think Xvid is a new hope... :)
It's the best.
Thanks a lot.

fufo

[Dali Lama]

Xvid doesn't have a separate iscd input like Nandub. Just use the scene detection tab in virtualdub. The defaults work fine with Xvid.

Bye,

Dali

[yokem55]

I always wondered if that setting in vdub actually did anything....I guess it does...is there a single "good" setting, or does it not make much difference, or is it largely content dependent?

[Dali Lama]

It can be content dependant, but the default values are good with xvid. With nandub, the new alternative scene detection slider was better, because you could lower it for dark movies and raise it for brighter ones. 215/64 I think is good. I think default is 206/64. But once again it doesn't make that much of a difference, especially with xvid.

Of note: Some people have increased both sliders to max values when encoding anime in nandub. I am not sure why. Maybe you guys could experiment and see if it helps with keyframe placement or something in vdub and xvid.

Bye,

Dali

[Nic]

Im not sure, but I think I remember that the scene change detection is set internally to 50%. I think its set with the intra threshold or something...I cant remember & I don't have the source in front of me....But I think thats right.

(Im sure someone will correct me if im wrong :) )

Cheers,
-Nic

[Acaila]

I thought it was 60%....

[Nic]

Actually looking through the source, it looks like scene change/i-frame decisions are determined on a threshold bias basis in the motion compensation...

i.e.
if (deviation(mblock) < sad - BIAS)
Make an I-frame

where the BIAS is set to 512 (the MPEG suggestion), but was once set to 432 (& in the motion_est.c file states that it was set to the suxen_drol suggested 150...but its not)

So, I think thats correct.....

-Nic

[FuFo]

Thanks a lot for the answers.
Have a NICE day.... :)

FuFo

[kilg0r3]

That is there is no way to tamper with the scenchange threshold? I tried the vdub controls but they didn't seem to have any effect.

[sysKin]

Originally posted by Nic
Actually looking through the source, it looks like scene change/i-frame decisions are determined on a threshold bias basis in the motion compensation...

i.e.
if (deviation(mblock) < sad - BIAS)
Make an I-frame

where the BIAS is set to 512 (the MPEG suggestion), but was once set to 432 (& in the motion_est.c file states that it was set to the suxen_drol suggested 150...but its not)

So, I think thats correct.....
-Nic

No no, this is I-macroblock decision, not I-frame. The I-frame is currently 0.5, look for "INTRA_THRESH" in encoder.c . It means that if there is too much intra macroblocks (more than 50% of all), then I frame is produced. (motionestimation() returns 1 to mark this)

[Nic]

I know that now :) That was from a quick flick through a while back, I dont know why this post has been dredged up really. :)

Good to see you here sysKin :) Still looking into the Motion code?

Cheers,
-Nic