a loooong months ago i posted:
i see the image "breathing"..."pulsing"...something like this.
now i find the way to show "how tmpgenc breath" !

simple script with an static background scene from lionking3
(main movie only with dvd2avi project):

source ....
xxxresize(320,240)
trim(2000,3000) # frames used from NTSC dvd, from PAL dvd the frames are in differents positions for the same scenes.

this scenes selected using trim from lionking3 ,
have the "hienas" paused in the background in big red color!
you can choose another movie but with a static scenes like that!

the GOP structure for ntsc animes are:
1, 5823, 2, 1, 15 .
choose the output file name and encode this sample!
you will need no more than 40 seconds, don't be lazy, do that!

see in the progress bar that tmpgenc take 15 frames and encode..
then take more 15 frames and encode again...
each step using 15 frames to encode..... !

now change the GOP structure to :
1, 5823, 2, 1, 30.
of course, it's not ok for animes but is for show the "breath"
choose another output file name and encode this sample!

see in the progress bar that tmpgenc take 30 frames and encode...
than take more 30 frames and encode again.....
each step using 30 frames to encode..... !

now load in powerdvd this 2 samples and see how the image is
"breathing" in the background... see the "hienas" in big red !
the red colors encrease and decrease in each interval,
the first sample with GOP 15, "breath faster" and
the sample with GOP 30 "breath" in differents intervals from the first sample.

with GOP 15 sometimes is hard to see but
with GOP 30 you will see it EASILY

seems that the GOP adjusts have direct influences in the "breath"
changing this values, change the "breath" intervals in the encode!

i know how to show it,if you do this samples but don't know why it happen!

can someone do it like i did and post the impressions please?
a long time i try to explain it, can't find a better way...
only doing samples i can show !

thanks!

The longer the GOP, the more visible the effect.
At a GOP of 25, you have a combination of 24 B and P frames. So when the I frame is inserted, it replenishes the stream with a less compressed frame, and that's your "breath" frame
Then the image starts to degrade again for the next 24 frames, and again, when the new I frame is inserted, you'll see like a light switch was turned on.
Moral of the story: Keep your GOP as small as possible, and no larger that 25

-kwag

And taht explain also why it is better to use short GOP for anime cartoons : their numerous "plain" colored surfaces suffer a lot from the degraded B frames.

Exactly
The shorter the GOP, the less degradation, so the effect is not that visible.
It's still there , but just harder to see.
Of course, too short of a GOP will then start to loose quality. So there's a tradeoff.
I think the minimum should be 10 (IBBPBBPBBP) and maximum should be 25 (IBBPBBPBBPBBPBBPBBPBBPBBP).

-kwag

thaaannnk yooouuuu boooyyyyyss!

i was waiting for this details from months:

"And taht explain also why it is better to use short GOP for anime cartoons : their numerous "plain" colored surfaces suffer a lot from the degraded B frames."

"Exactly
The shorter the GOP, the less degradation, so the effect is not that visible.
I think the minimum should be 10 (IBBPBBPBBP)
and maximum should be 25 (IBBPBBPBBPBBPBBPBBPBBPBBP)."