Change GOP size during recording?

[reboot]

I know how to do this in WinTV2k, with the tweak from cask/amontillado...is there a way to do this in GBPVR?
Or does the setting in the reg for wintv2k also work in gbpvr?
Ideally, I'd like it to be 5 or 6.

[stefan]

What is GOP size? What would changing it to 5 or 6 (what is the default, btw) accomplish? *curious*

[reboot]

GOP is a Group Of Pictures.
DVD standard is 18 for NTSC, and 15 for PAL, although NTSC will also do 15.
Each GOP contains one I frame (full picture) and (usually) alternating P and B frames.
The P and B frames get part of their data from the preceeding, and following frames.
The more I frames you have, the higher quality the video, at a cost of larger files.
In a perfect world, using mpeg-2 compression, one could use a GOP of 1, being an I frame, but the video would be huge, and won't play in most (some?) dvd players, nor will some authoring apps even accept it as a standard mpeg.
What this means, is that a GOP of 6 (for example) will have 5 I frames per second (NTSC 29.97fps), and 4 I frames in PAL.
At the same bitrate you are currently using, you end up with slightly larger files, and better quality, without having to dramatically increase bitrate.
With a GOP of 5, I can fit two hours of TV on to dvdr, once commercials are edited.
I've tested this in tmpgenc, Canopus Procoder, and Mainconcept, and the quality is noticably better in most cases, especially high motion scenes.

As a bonus, a smaller GOP allows most editors to cut with more accuracy, because those that can only cut on an I frame, have more I frames per second, thus you can do better cuts, without having to re-encode.

[bgowland]

Please sir - can I go home now? My brain is full.

[stefan]

I asked for it - and almost regret I did. Excellent info, though =)

[reboot]

Heh, well, you asked!
Still wondering if sub has seen this, or anyone else knows.

[sub]

Yes, I've seen this post.

I dont expose any way in GB-PVR for you to set the GOP size. It'd probably honour any GOP size registry setting that Hauppauge have, but I havn't tried it myself.

[reboot]

Thanks. I'll try the Hauppauge change, and see if gbpvr picks it up.