What affects What (Video/Audio/Sub, etc.)

[hypnoticbob]

I'm curious. Let's start off with the SVCD standard and try NOT to get outside of SVCD (xSVCD) for now. How do other influences affect the max video bitrate? I mean, you have Audio bitrate, (possible) subtitles, image quality priority (does this affect available space at all? or any filters in general...?), resolution (although this would be outside the specs of svcd, but let's add it for curiousity reasoning), "title picture"/"changecd picture", chapters (fixed/dvd)? I think that's about it. I know it's probably a lot of useless crap, but curiousity fuels the mind ;) or maybe it's oxygen, whatever...

[markrb]

Well, of course, there is the standard of SVCD which, I believe, states a max combined video and audio bitrate of 2754 of which 224 is audio. This leaves 2530 as the Max video bitrate.

As to the chapter points and the title/change cd pictures these are in fact outside the video itself and in a different place on the cd. For the most part they take up almost no room as the chapter points are simply software pointers and have no direct affect on the video. So, yes these do take up room on the cd, but for the most part they are so small, about 1mb or so, they don't affect the video size.

As to resolution, it in and of itself has no direct effect on the video size, however the greater you make the resolution the more bits it requires to look as good. Just consider many of the videos I am sure you have downloaded on the net. If you maximaxe the image most times it looks blocky and bad and when you make the video smaller it looks better. The same applies here, but what we are doing when increasing the resolution is telling the video to make itself that big as default. Alocate more bits and it will look better. That is why a VCD at 1150 bitrate may look as good if not better then an svcd at a much higher bitrate. SVCD's have a higher resolution requiring more bits, but when done right SVCD's look better, because of the combination of increased bitrate and resolution. In my case I do one better. I make all my videos closer to DVD spec. My player is an aboration and can play up to 5500Kbit. So I use it and make my videos full DVD size with as high a bitrate as can fit on 3cd's, since it's a 3cd changer.


Personally I have not known Image Quality priority to change file size. I guess it could since you are altering the way the bits are alocated, but in my experience I haven't seen it do much if anything for filesize. I tend to prefer I higher then the standard number. I use 22 to 24 myself.

Filters and such can change or alter many things. That is what they are afterall. They are meant to alter the video or audio and each is different. You must consider each on it's own basis as to how it affects the SVCD.

In the end what is the common point of what you are asking is not so much about how each of these things affects the bitrate. It's all about size. This is what truly affects bitrates. The more you add onto the same number of discs the smaller space you have to put that video into. What DVD2SVCD does is make a call as to how big can I make this so it will fit onto the number of cd's selected.

Consider this of an average 90 minute movie.
BTW these are purely educated guesses.

Each 224 Audio Stream is about 95mb's
Each Subtitle Stream is about 5mb's
The title and change cd picture in reality have about a 0mb file size
since I believe the space is reserved even if you don't use them.

I hope I am right and that this helps.

Mark

[hypnoticbob]

Your information about it all helps, alot. There are many things that I wasn't sure of (as far as size, etc) that might attribute to loss of quality, because of sufficient space. Do you use VBR for you high quality rips or do you use CBR for continuously high bitrate for all areas? My DVD can (so I have heard) support up to 8000kb XSVCDs. I would like to test this method, but I am unsure of whether CBR or VBR would be best for no more than 3cds. Most films are less than two hours, but whether they are more or not does not affect my decision of having a max of 3cds. Thanks ;)

[markrb]

In theory CBR can never be worse then VBR and may be better. Consider that CBR uses the same bits on each scene no matter what is in it.
This is a waste of space however. Why use the same amount of bits on a complex scene then you would on a black screen. So in space VBR will always be better.
Now you come down to the last part, the software making the choice on what needs those few bits and what needs those extra bits. CCE is pretty good and gets better with each pass as it uses the previous pass to decide if it made the right choice and then adjusts the bits used.
3-4 passes is about as good as it gets though. If I have the time I might use 5 passes since I have a very fast machine and I am asleep anyway.

The only time I use CBR is when I am in a rush and the number of cd's won't increase. CBR will always be faster since it's only doing one pass, so it's only 1 x movie length x CCE (or TMPG) speed.
Where VBR is number of passes(+1 for VAF) x movie length x CCE speed.

Have a read through the Q+A and the quick guide and faq in the basics section.

Mark

[chainsaw135]

To add with what markrb as stated, i use 5 pass all the time since my machine is fast and i have 2 machines. I myself can tell a difference in some movies when i use 5 passes v's 4.