Bitrate for HQ-SVCD

[djbronko]

Hi alltogether!

I want to make SVCD's with TMPG, and I've read a lot about the SVCD-Standard, and about VBR and CBR; but there are two questions that remain:

1) The SVCD specs allow a max Bitrate of 2.600.000 Bit/s (I also read that the standard allows to go up to 2.824.000, but this is not supplied by Hardware-players because of the built in 2x-speed-cdrom-drives). Question: Why does the SVCD-Default-Template offer 2.520.000 Bit/s Video-Bitrate, plus 224.000 Bit/s Audio Bitrate, what makes, ohm, ..., 2.744.000, which exceeds the specs?
2)
I want quality, not encoding speed. I also have the possibility to burn 99min-CD's, which should be compatible with every Standard-CD-Player. The question:
Should I use VBR or CBR? I think CBR is the better choice if I don't want to save space. But does VBR mean "save space where possible" (and so allow more length) or "save space and use the won bytes to encode other passages with more than the maximum bitrate", so that difficult scenes may use more than 2.600.000 Bits/s ??? For that, the data must be buffered, I think.
Or is this idea just nonsens?

[Kedirekin]

There is quite a bit of argument over SVCD bitrates, so you'll probably get lots of conflicting replies. I don't consider myself an expert, but for my part, I believe the spec says 2600 kbps is the max allowed video bitrate, and you can have 224 kbps audio on top of that. Oddly, it seems to exclude video bitrates above 2600 kbps, even if you lower the audio bitrate.

Incidentally, I believe the 2x mode2 form2 bitrate is 2,788,800 b/s (2324 B/sector * 150 sectors/sec * 8 b/B). And before you say it, I know that 2600 + 224 != 2,788. I don't claim to understand how they came up with the SVCD spec. Perhaps that is why the TMpg template sets the video bitrate to 2520 kbps.

As for VBR, once again you'll probably get argument over exceeding the max bitrate. However, for the most part, I think you can assume the VBR will save space where possible - it won't exceed the max bitrate you specify (or at least, not by much).

[djbronko]

Thanks Kedirekin for your fast answer; so I'm not the only one who doesn't completely understand this whole SVCD-Spec-stuff...

I just have another question, concerning the "source aspect ratio" tab: I don't understand what this really is for. I mean, TMPG could get the aspect ratio from the size of the original input (Probably that's what it does if I say 1:1 VGA).
I ran into problems when I recorded a movie from TV in 720x576 which was 16:9. I wanted to kill the black tabs, so I went to "clip frame" and have thrown them away, so that a resolution of 720x410 was left. Now what should I choose as "Source aspect ratio" ? In 16:9 it's squeezed, even in 4:3, only 1:1 seems OK. Are these ratios maybe only to save the work of clipping the frame?
And what is most important for me: Does the "Source aspect ratio" concern if the movie can be played on a hardware-player?
I mean, I don't want to choose 1:1 (because the picture looks best), if all the players understand only 4:3.

[Kedirekin]

Someone else could probably give a better answer (hint, hint).

I think the source aspect ratios settings are there to help TMpg do some resize wizardry. For example, if you choose a source aspect of 16:9, and your output setting is 4:3, TMpg may add black borders automatically to letterbox the movie (depending also (I think) on the Video Arrange Method).

I personally find it very confusing and wish the stuff wasn't even there (I've had it mess up more than one encode), but some people absolutely love it.

In your case, I'm not sure what to suggest - I'm not even sure if this resize wizardry takes place before or after the clip-frame filter. If it were me, I think I'd select settings that don't do any wizardry (1:1, Full Screen, I think).

Other than this resize/borders stuff, I don't think source aspect impacts your output mpg at all. Just make sure you have the output aspect ratio you want selected on the Video tab.

[djbronko]

Thanks for your hints, I finally found a page that aswered most of my questions (in german):
http://www.edv-tip.de/svcd/index.htm

So if someone wants to know how VBV works, or which Bitrate is best, here's the answer.