techniques to fill a cd with svcd

[rekonrad]

I am quite tired of guessing the bitrate and quantum values to get an avi file to ultimately fit more or less perfectly on a cd (795 megs) under SVCD. Has anyone devised a method or a chart, using the original values of the avi to do this?

Thanks!

[shadowcat45]

Well, this is simply not possible for SVCD.
As you probably know, SVCD has Variable Bit Rate, therefore 10 minutes of Video can have very varying size in MByte. So it will be always an estimate. Additionaly, besides VBR, SVCD accepts lower avreage bitrates than the max with (depending on source material) few visible effects (e.g. 2000 kbit), broadening the possible size of (the exemplary) 10 minutes video.
It is said that around 30 minutes of SVCD mpeg fit on a CD, but I had fit up to 45 minutes until now, depending on the source material. Pre-processing, especially noise reducion (e.g. yuvdenoise within the mjpegtools) helps mostly to reduce the final mpeg and fit more (with default mpeg2enc values).

Questions like this also occur frequently on the mjpeg mailinglist or in the vcdimager forum.

One possibility (not ready programmed yet) is 2-pass encoding of the mpeg, where in the first run, an analysis is made which can help to either maximize the bitrate or fit on a CD (by reducing the bitrate).
Another proposal was, go through the movie, take some frames out at random (e.g. 250 = 10 sec PAL), encode it, and use this as an estimate variable. This is of course based on statistics, if you get the wrong "look into the sky" frames with almost no motion, you will underestimate badly, additionaly, taking frames at random can make the P and B frames grow, as the frames can be very different from each other, thus overestimating the size.

So, there is simply no easy solution to do this estimate. In your case, additional factors occur because of the AVI base you will take. Does it have the right framerate ? If no, e.g. adding frames will have an influence on the resulting mpeg2 (as this is done mostly by copying frames, which are of course equal to its precedessor and give very small P or B frames).

VCD, with its CBR (both for audio and video) allow more accurate estimation.

[rekonrad]

Thanks for your lengthy reply. My knowledge of the concepts you spoke of are limited but I did find the correct setting and filled most of the disk. I would be interested to know when a two pass method as you described would be developed. Perhaps this is a good forum to get such updates.

Richard

[mats.hogberg]

To make it simple:
Use a bit rate calculator (see tools)
CBR SVCD is really exact and simple - just enter the duration of the AVI and tweak the audio/video bit rates until you get the desired file size. Many calcs lets you specify # of CDs of a given capacity, and returns the bit rate to use.
VBR SVCD is not that exact, but in theory you just use average bit rate instead of the constant bit rate. The settings for max and min bit rate doesn't matter. Now, at least not TMPGEnc, the mpeg encoder seldom reaches this average bit rate exactly, so you have to allow for a slightly bigger file than the calc suggests (lower the average bitrate somewhat).
Personally, I use this calc, and lower the bitrate it suggests by about 5%. That will give me plenty of room for menu stills and the rest of overhead.

/Mats

[rekonrad]

Thanks for the tips. I use transcode to encode my avi's and one of the options is the QUANTUM value. The lower the number, the greater quality of the output. I don't see such an option in the windows software you suggested. Altering the QUANTUM value radically changes the final size of the project.

Any ideas?

Thanks,
Richard

[mats.hogberg]

Ah... I see - a fellow Linux user? Have only used transcode via DVD::RIP, but never done any AVI to (S)VCD. Take a look at the man page for mpeg2enc (that transcode uses for SVCD encoding). I think there's an option to set the average bit rate somewhere in there. Whish there was some good docs for this. Most questions in the mailing lists get answers that starts with "Just look in the source code..." - OK, I'm a pretty good programmer, but to read the source code to understand how to use an encoder?!? No big wonder Linux has some way to go before it hits everyones desktop!
I've found some transcode avi2svcd scripts here and there - search the web!

/Mats

[buildid]

try avidemux i use it for a long time , and iam verry pleased with it