Question about bitrate redistribution vs quant matrix used

[Insomniak4700]

I've read a lot about redistribution (and tried it on a couple of discs), and I was wondering what happens If I choose different quantization matrices for the main feature and for the extras. (let's say avamat6 for movie and avamat7 for extra).

Is the bitrate redistribution done on a per VTS basis? Will my extras matrix be used or is the main feature matrix used through out the whole redistribution process?

(Am I being clear? :)

[jdobbs]

By default redistribution is only done to the main feature VTS. If you select "redist_all=1" it will be applied to all (not on a per VTS basis -- the constant Q will go across the entire disc).

[Insomniak4700]

Thanks, but sorry I wasen't clear..
redist_all is enabled....

A single Q value is used for redistribution, but is a single matrix used throughout the whole process, or is the specified matrix used?

Let's say VTS_01 is main movie... avamat6 is specified. I know redistribution will be done using this matrix.

now if redist_all is enabled, and let's say VTS_02 is the extras, and I selected avamat7 for extras... will avamat7 will be used for redistribution of VTS_02?

[jdobbs]

No. Matrices are not used for Q encoding, including redistribution. That's mainly true because most of the matrix selections are based upon bitrate -- which is unknown during Q encoding (at least until it is complete). You'll also find that changing the matrix will significantly alter the Q value -- and could leave you with wild swings in quality, even though you have a constant specified Q (defeating its purpose).

The matrix selection for extras is also left out (it's all in the same routine right now) -- but I guess I could probably change that for redistribution. It would make the extras a different quality level than non-extras, though. If you're looking for constant quality across the entire disc -- you really need to use a single Q and a single matrix.

[Insomniak4700]

Maybe redistributing the extras (with the extras matrix) could be a good idea.... on most full disc encodes, not a lot of bitrate is left for discs packed w/ extras.. (and so far, it seems redist helps a lot in low bitrate situations)

I tried backing up my Ghost Rider R1 dvd this week, and I wasen't able to get good results until I used the redist_all option..

[jdobbs]

That probably means the extras were on the edge of acceptable in terms of bitrate on the original -- so the reduction put it over that edge. With "redist_all" set it is very likely you took some of the available space from the main feature and added it to the extras, keeping them at a viewable level.

[Sharc]

@Insomniak4700:
If you like to explore Q, matrices and redistribution in more detail you may want to try out RB-Opt. If you are using CCE you can freely select matrices and redistributions on a per VTS basis.

[Insomniak4700]

Thanks Sharc, I'm currently using RBOpt for that purpose...
But I always love seeing jdobbs adding cool features to RB ;)