Gop

[Master Yoda]

Under GOP in CCE2.50 i dont tick close all GOPS, but whats the difference between having the GOP Sequence as M=3 N/M=5 and M=3 N/M=4.?

As most guides say to have the N/M = 4, but CCE default is N/M=5

[Kedirekin]

Look at GOP sequence as you change the values.

Personally I've never been comfortable with the N, N/M thing. It just isn't intuitive to me. I much prefer the I/P/B settings ala TMpegEnc (at least, what I remember of them).


From the CCE manual:


By changing the M value, the number of B pictures
can be changed, and by changing the N/M value, the number of
P pictures can be changed. The standard setting is M = 3 and
N/M = 5.


Perhaps another way to think of it is N/M defines the number of subgroups and N defines the number of frames in a subgroup.

So for M=3, N/M=5, there are 5 subgroups of 3 frames (IBBPBBPBBPBBPBB).

With M=3, N/M=4, there are 4 subgroups of 3 frames (IBBPBBPBBPBB).

My feeling is M=3, N/M=4 is the best setting for 24 fps material, and M=3, N/M=5 is best for 30 fps material. In both cases, one GOP comes out to approximately ½ second.

[RB]

Basically, less pictures in a GOP means better quality, but also requires more bitrate. For average bitrates above 4000 kbps I'd use 3/4 and below that 3/5. It really has nothing to do with the frame rate.