CCE GOP Settings for DVD Conv

[Blackout]

hi,

in regards to the n/m setting for CCE, i have seen several ppl change this from the standard setting of n/m=5 to n/m = 4. Can anyone explain exactly why this is done? Does it affect the sync of video with audio? If the original source is Film, what is the correct setting here...im asssuming the GOP amount relates directly to framerate...?

With my experiments with some DVD-source film material, i seem to get a slightly more stable and noise free picture with n/m=5, however most guides suggest it to be 4. DVD Maestro seems to be happy accepting either file so ill be buggered if i know what the correct setting is.

Thanks in advance,

Blackout

[Flood]

m and n/m in CCE represents the ratio and configuration of Predictive (P) and Bidirectionaly-Predictive (B) frames to Intra (I) frames; it has nothing at all to do with frame rate.

Because an I frame represents an entire single frame/field (with no reference to any other frames), upon which P and B can be based, the more often you have an I frame the higher quality your output should be, at the expense of bandwidth (I frames are typically largest).

I frames also represent a discrete point at which the stream can be started from, which is why all GOPs must start with an I frame, so that the decoder can instantly seek to any given GOP and begin playback.

You can find a good "beginner" reference to mpeg-2 at: http://www.puremotion.com/videoediting/reference/technical/mpegvideo/

A more advanced conceptual reference: http://www.bbc.co.uk/rd/pubs/papers/paper_14/paper_14.html

[Blackout]

Hi flood,

thanks for that; i kinda know that complex technical rundown, i really just want to know if ppl are putting this setting as 4 or 5 for DVD conversions....

regards,
blackout

[jdobbs]

Blackout,

I can tell you why I set it to 4 -- because when I set it to 5 I sometimes get GOPs that are too long and are rejected by DVDMaestro or ReelDVD -- I'm not really sure why it happens, as you would think you'd alway get GOPs that are 15 frames long (IBBPBBPBBPBBPBB) but the rejection happens all the time. An interesting sidenote is that I can ALWAYS import the resulting file (when I've set it to 5) in SpruceUP (even the one that is rejected by others). Go figure.

jdobbs

[Blackout]

Thanks jd, thats exactly the feedback i wanted.

I did a few more tests on some other movie material and it seems 4 is better after all....i seem to get a "very slight" fuzzy pulsing of the image when its on 5.

I think most DVD studio houses code commercial DVDs to 4. (ie 12 frames in a group)...so it makes sense to keep it the same.

Blackout