VBV buffer size for VCD and SVCD

[Jestorius]

What is the correct VBV buffer size for VCD and SVCD?

[Jestorius]

Ok, what about pocket size?

[kinneera]

Based on TMPGEnc and bbMPEG defaults, VBV for VCD and SVCD is 40 and 112 respectively.

[swiftsword]

My burning question is - does VBV buffer really matter with MPEG-1? I'm doing XVCD @ 2500 kbps and I'm figuring the bigger the buffer, the better - to the point where you exceed the actual buffer size of the decoder.
anybody know what difference buffer size makes?

Thanks,


Oliver

[Jestorius]

Thanks, I'm using Tmpgenc. I just wonder if the VBV buffer size is for the decoder chipset in the DVD player? I can't find any info about VBV buffer size and pocket size.

[adam]

The buffer size of the decoder is fixed, you can't adjust that.A larger VBV value doesnt mean you'll get a larger buffer. VBV stands for video buffer verifier. Its a hypothetical value which controls your data rate being sent to the decoder's buffer, so that it does not overflow or underflow. If its too low then the data rate won't be fast enough and I suppose at that point you won't have enough data to render that full second of picture, resulting in garbage. I think an overflow would cause a similar effect also.

There is a formula for determining VBV, damned if I know it though. Having an incorrect VBV can affect playback adversely, but you can't tweak the level to squeeze more quality out of your encode. For this reason its best let the encoder pick the appropriate value for you.

Also I think most hardware decoders don't even use the VBV buffer anyway they use time stamps instead.

Jestorius: I've never heard of pocket size, are you sure you don't mean packetsize?

<font size=-1>[ This Message was edited by: adam on 2001-11-27 15:43:25 ]</font>

[Jestorius]

Sorry, it's packetsize.

[Jestorius]

Thanks adam, this is the info I was looking for. Can you tell me please what function the packetsize has?

[mb1]

This link explains vbv buffer in detail (but in german !):
http://www.edv-tipp.de/svcd/236_vbv_mux.htm

VBV according to IEC 62107 (SVCD-Norm):
1.835.008 bits /8 /1024 = 224 KB

Tmpeg has wrong default svcd-setting (112 KB).
It is better to manually set it to 224 KB.

SVCD-muxing with bbMPEG requires 230 Kb (=224 KB).

Wrong VBV Buffer results in unflawless playing, so simply choose max vbv always.
But be careful, programs sometimes name it wrong. In avi2mpg2 f.e. you have to set value 112.

If you have already encodet with a too low vbv buffer, simply remux with bbmpeg.

regards
mb1

[Jestorius]

Thank you for all of you.
mb1 - the site is very god. Thanks.