very long GOPs in TMPG... good or bad idea?

[Mug Funky]

hey-o, everybody :)

i've been encoding SVCD with very long GOPs (like, 48 frames). the results look pretty good, but i've yet to try playing back on my standalone.

are there any badnesses involved in doing this?

(btw, i'm encoding anime, fairly low motion, in PAL).

i'm just curious really, i figure if my machine can handle it (don't know that yet), then i'll keep it up.

the main probs i can foresee would be memory consumption and error tolerance (ie. the long GOP would make a scratch on the disc last up to 2 seconds).

anyone tried this? or am i being stupid?

[wmansir]

I would definitely give it a try on your standalone before you build to big a collection and find you can only play them on a computer (which would mean divx, rv9 or xvid would have been better choices).

I think you may run into trouble. My Apex player has subtle (but annoying) problems when I use a GOP length over 12. I use to use 15 until I realized what the problem was. In my case the problem was most visible in dark scenes, but not very apparent in normal or bright ones. I believe 12 is to spec, or at lease a common limitation, so even if your current player can handle longer GOPs you may want to keep it at 12 for compatibility with future players.

[jshumate]

Although you may have no interest in this at all, if one day you want to convert your SVCDs to DVD, the very long GOPs are going to bite you. DVD specs require that GOPs be 18 frames or less and some authoring programs, such as the old DVD Maestro, actually enforce 15 frame GOPs for authoring. Of course, there are other issues with converting SVCD to DVD (ie. 44 vs. 48 Khz audio and resolution). Anything above 18 frame GOPs may (or may not) cause playback problems on a standalone DVD player.

I only bring this up because as the price of DVD burners and media drops, at some point DVD burners are going to be as common as CD-R burners are now. When that happens, SVCD will be a dead format and support for it in the future may start to disappear from stand alone DVD players. One day you may wish to convert your SVCDs to DVD and you may regret having those long GOPs. Of course, you could always re-encode it, but I would expect quality to suffer from that.

[Kika]

On Animes, you can use longer GOPs, but only(!) for VCD/SVCD-Use. There's no "clean" way to put Videos, encodet with long GOPs, onto DVDs.

Good Settings for Anime in TMPGenc:

GOP: 1:5:3:1
Rate Control: CQ-Mode, B-Picture Spoilage 10, P-Picture Spoilage -5
CG-Smooth-Matrix