What is the cell bitrate?

[NaN]

Hi!

Unfortunatly I wasn't able to find an explanation of the cell bitrate as it is reported in the status window during prepare.

A simple multiplication with 2 (like the targetsectors) doesn't seem to make sense, since I sometimes get values like 5500kbs (as max value) whereas the dvd-spec says 10.8Mbs is the limit.

The max value is usually quite close to the cell average value (e.g. 5000kbs for above max value), so I'm a bit confused. Usual bitrates would be like 4500kbs average, 9000kbs max (with 2-3 ac3 audio tracks).

Thanks for helping me out!

Cheers, NaN

[jdobbs]

You are confusing the maximum allowable and the maximum needed. The value displayed in the window is the maximum actually used as the average bitrate.

Also 10.8Mbs includes all bitrates combined (audio, video, and subpictures) -- not just video. DVD-RB is reporting the video-only bitrates.

[dragongodz]

Also 10.8Mbs includes all bitrates combined (audio, video, and subpictures) -- not just video
and muxxing overhead of course. its like the 9.8Mbit video maximum, thats for if there is no other streams. once you start adding audio etc then that needs to be reduced by the equivilent streams amount aswell(or a little extra even to allow for increased overheads for multiple streams).

yes i know DVD-RB already does the reduction based on other streams kept. this is simply to make it clear to anyone that reads this that values need to be taken in their context and DVD-RB is already doing that. :D

[NaN]

So what does the following mean:


HIGH/LOW/AVERAGE Cell Bitrates: 5.974/159/4.339 Kbs


Average (video only) bitrate is 4339kbs. Ok. I somehow don't understand how do you determine what the high bitrate is? How do you decide "what the maximum needed" is?

Thanks for your replies!

Cheers, NaN

[jdobbs]

The effective average bitrate is determined by:

1. The size of the source.
2. Frame rate of the source.
3. Space available for output.
4. Amount of space used by the original (dynamically assigned mode)

The maximum bitrate is determined by:

1. Maximum bitrate allowed by DVD
2. Amount of bitrate required by kept audio.

First it looks at the amount of space on disc that contains data that will not be compressed (audio, subpictures, small VTSs, menus). It then decides how much is left for the video. The remaining space determines the overall bitrate. If dynamic is selected the available space is allocated consistent with the way it was distributed (by cell) on the original DVD. The HIGH/LOW/AVERAGE shows the resultant bitrates from that allocation to cells.

[NaN]

Well...so this high bitrate value is the result of the dynamic assignment. So the basic bitrate distribution of the original dvd is maintained.

Great! Thanks for taking the time to explain! A riddle less ;-))

Cheers, NaN