GOP questions in Cinema Craft Basic v2.7

[schrakapouet]

Hi,

I'm using Cinema Craft Basic ver. 2.7 but I'm curious about some Advanced video settings I don't know how to use them and what they are exactly doing :

First in which case do I need to change the GOP sequence ? What would the result in the video size or/and quality if I rather choose /IBBPBBPBBPBBPBBP/ (M=3 -N/M=5) or /IBPBPBPBPB/ (M=2-N/M=5) and then /IPPPPIPPPPIPPPP/ (M=1N/M=5) ?

And by the way what is M and M/N ? (and again why would I want to use them ?)

What is a GOP header ? ...and SEQ Header ?

Thanks

[Delta2]

Hi,

I'm using Cinema Craft Basic ver. 2.7 but I'm curious about some Advanced video settings I don't know how to use them and what they are exactly doing :

First in which case do I need to change the GOP sequence ? What would the result in the video size or/and quality if I rather choose /IBBPBBPBBPBBPBBP/ (M=3 -N/M=5) or /IBPBPBPBPB/ (M=2-N/M=5) and then /IPPPPIPPPPIPPPP/ (M=1N/M=5) ?

And by the way what is M and M/N ? (and again why would I want to use them ?)

What is a GOP header ? ...and SEQ Header ?

Thanks

GOP = Group Of Pictures

http://en.wikipedia.org/wiki/Group_of_pictures

basically it tells you how pictures are arranged in a mpeg-2 stream, and the compression technics of the mpeg-2 format

It affects motion smooth when you convert a original PAL to NTSC, or vice-versa, and when you apply pulldown, therefore the best settings are :

PAL to PAL : M/N = 3/4
PAL to NTSC when applying pulldown afterwards : M/N = 3/4
NTSC to NTSC : M/N = 3/5
NTSC to PAL : M/N = 3/4

[jman98]

Delta2's post is correct, but to elaborate a bit on it, B and P frames are what enables MPEG video to compress. More B and P frames will lead to higher compression of the video (and thus smaller file sizes). Fewer B and P frames will lead to less compressed video (and thus larger file sizes). PAL video for DVD has a limit that GOPs can't be more than 15 frames. NTSC video for DVD allows up to 18 frames. M=3 and N/M = 4 would be good settings for you since you live in PAL land. I would not recommend the other settings you asked about. What I suggested is exactly what commercial PAL DVDs use.

[schrakapouet]

Thanks a lot for your answers ! Always good to learn stuff about compression, this forum is really cool.