CCE SP 2.5 Question

[Booooom]

Hello all,
I am using DVD2SVCD with CCE SP 2.5.
1. When I use CBR and Check the Create Vaf File checkbox, does that mean I actually doing 2pass CBR. Does 2.5 has 2pass CBR at all and what are 2pass CBR advantages

2. Is there any need at all for checking the Vaf file while encoding with CBR (in terms of better encoding).

Thanks.

[adam]

1) If you have CCE set to 1-pass CBR than no, you are not doing multiple passes by enabling the creation of the .vaf file. The .vaf file is simply a txt file that records certain information about your source, which is gained through each pass of encoding. If you encode in only 1 pass than this information does absolutely nothing because it does not exist until that first pass is done, but if you decide to do a second pass then you can reuse this information.

If you wanted to do 2 pass CBR you would have to do it manually, by creating a .vaf file the first time and then reusing it in the second encode. The information gained from the first pass will still be useful even during the 2nd CBR encode because you will gain better accuracy regarding motion vectors and quantization, even if you are limited to the same number of bits every second, ie: CBR. But, the gain in doing a second pass when encoding in CBR is minimal at best. If you are limited to CBR than I wouldn't bother with more than 1 pass. A much better option is to do multipass VBR instead.

2) If you are doing CBR encoding then no, there really isn't any reason to create the .vaf file. Its certainly not going to help the quality of that pass, and there's really not much point in doing any subsequent passes if you are only using CBR. Of course enabling the creation of the .vaf won't hurt anything either. From my experience it doesn't slow down encoding, and if you are encoding in 1 pass then it simply won't be used at all. If, however, you need to re-encode it differently for some reason, then you can reuse the .vaf file to possibly give you a slight increase in quality.

Another benefit is that once the .vaf is created you can use CCE's advanced settings to tweak bitrate and quantization. Of course if you are encoding in CBR its not like there's much you can do in this regard, but its still a nice tool to see an objective analysis of your file's quality.

[Booooom]

Hi,
Thanks for replying.
I am bothered with what you said regarding VBR: "A much better option is to do multipass VBR instead. "

I convert Avi to SVCD. I set (In DVD2SVCD) the Min Bitrate to be 2300, the mean avg. to be 2300 as well and the max avg. to be 2330.
In that case (while i let the mean Bitrate to be very high - almost 2500) is there any benefit to use multipass VBR?

It was my understanding that you should use VBR whenever you have a need for space thus you "sucrifice bits" in slow moving scenes for fast moving scenes.

Thanks.

[adam]

If your bitrate is already maxed out than no, you're not going to gain anything from using VBR. Though, you might be able to fit your movie on less disks and still achieve releatively the same level of quality by using VBR and a lower average bitrate.

Also realize that you may still have some room left to allow the bitrate to fluctuate by using VBR. The SVCD max bitrate limit is 2778. Factoring in an audio bitrate of 192-224kbits you've still got around 200kbits or so to play with. This seems neglible but with SVCD every bit really does count.

Another thing to consider is that many if not most hardware SVCD players actually can play bitrates well above the arbitrary 2778kbit limit that the standard sets. You can achieve significantly higher quality by keeping your average as it is, raising your max setting, and using VBR instead. Of course this is a personal decision because you are sacrificing some compatiblity in exchange for higher quality.