CBR or VBR for VCD for authoring?

[Bob Korn]

I am using TMPGencPlus to encode short video clips (15-40 seconds each) for a client who is authoring a CDrom. They are either 320x240 or 640x480.

I've been reading as much as I can about this, but still don't know the answer:

On one hand, CBR of 1150 is the standard. Yet using a VBR up to 2300-2500 seems to be a possibility. The end-users of the CDrom will will have a variety of computers - some new, some older - just like the regular population.

There is not a lot of motion in the video. If I were to use 2-pass VBR, what would be a safe range? Or should I stick with CBR? And should I encode the 640x480 clips at a higher bitrate than the 320-x240's?

Thanks!

[ZippyP.]

On one hand, CBR of 1150 is the standard.

The end-users of the CDrom will will have a variety of computers - some new, some older - just like the regular population.

..... should I stick with CBR?

And should I encode the 640x480 clips at a higher bitrate than the 320-x240's?

1150 is the standard for VCD, you are not making a VCD. You are making an mpeg for playing on a computer and so your are not bound by any of the VCD standards. Since your resolutions are exceeding the standards, then your bitrate needs to be raised as well to keep it looking good.

VBR is great if you are trying to keep the file size to a minimum, i.e. getting more minutes per disk. If that is not a concern then just turn up the CBR bitrate to a level where the video is good to your eye. The files will get bigger, but it doesn't sound like that is a concern when the videos are so short.

640X480 has 4X the resolution of 320x240, better make your bitrate 4x higher as well to maintain quality. What your bitrate should be is up to you, since I know nothing of your source. Try some test encodes at several rates and decide for yourself. Higher rates are better up to a level beyond which it will start to make very little or no difference.

Good luck.

[Bob Korn]

Thanks for the quick response!

But since the MPEG files I'm giving my client will be used in a CDrom, don't they still need to be within VCD standards to play well on most computers? If not, what would be the highest bitrate I could set before it wouldn't play well on some older computers?

As you guessed, size of the files is not an issue. The original video is very high quality that we recently shot, and I am using AVI files of it (from an Avid XpressDV) to encode.

[ZippyP.]

But since the MPEG files I'm giving my client will be used in a CDrom, don't they still need to be within VCD standards to play well on most computers? If not, what would be the highest bitrate I could set before it wouldn't play well on some older computers?

The processing power of most PC's far exceeds DVD players, they should handle almost any type of mpeg. How high can you go? Beats me but DVD's are up to 8,000 KB/s (max.) and you shouldn't need to go anything near that if your footage is as good as you say. As long as you intend it for pentium class computers (200 MHz or more) then I don't think you'll have any problems. Try your lower res stuff at 2,000 Kb/s and the higher res at 6,000 for a start.