Constant Bitrate vs 2 pass VBR

[too2buff]

whats the difference between Constant Bitrate and 2 pass VBR ?

I want to encode a dvd to the highest bitrate possible , so I ran bitrate calculator and it said maximum 9500 and average 5000

but what would be the different if I set the bitrate at constant 8000

and are retail dvd's constant bitrates or variable bitrates ? I always assumed that they were constant because I usually never see any noise or quality loss. I have only noticed that when I was watching HDTV

what should I do ?

[helix]

Constant bitrate applies applies one bitrate that never changes to each fram of the movie. It's good if you want predictable file sizes and a quicker encode. What 2 pass VBR does is it first scans the video and decides on the "best" bitrate for a frame. Since it will will apply a lower bitrate to low-motion scenes that don't need a high bitrate, you will get a lower file size but practilly the same quality. The downside is that it will take twice as long and yeild an unpredictable file size. As for what retail DVDs are, i'm not sure, I think they might be VBR.

[Lagoon]

Retail DVDs are always VBR, CBR would yield catastrophic result for anything longer than 90 mins maybe even less.

helix, the size isnt unpredictable with 2-pass VBR, since you can specify an average bitrate it will always be the correct size, what is unpredictable is the Constant Quality mode.

I'd only use CBR for 60 mins or less footage, which allows a CBR of 8000+ kbits.

BTW there are noise and quality loss in most of the retail DVDs, my quality-freak eyes can see them :devil:

[helix]

Hmmm, I didn't know that VBR was predictable, thanks.

[Sunhillow]

VBR is not predictable, but 2-pass-VBR is.

In the first pass the encoder examines the source material and calculates bitrate distribution, the encoding is done in the second pass.