Dynamically assign bitrate, always on

[Msc_Alex]

Just a question about turning on "Dynamically Assign Cell Bitrates" always.

When backing up dvd's which have constant bitrate say 8000 kbps my
assumption was that RB would use same settings in bitrate for all cells.
In these cases I normally turn of DACB and let cce do the work
(my settings are normally 3 pass vbr cce). Was this wrong ?


quote:
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- The bitrate calculating algorithm can now examine the original allocation by Cell and assign bitrates to each cell consistent with that of the original DVD. This essentially uses the original DVD as a "first pass" and gives more bandwidth to cells that need it. This could (theoretically) result in better quality. This "dynamic" bitrate allocation can be enabled by selecting "Dynamically Assign Cell Bitrates" from the "Modes" menu.
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[onesoul]

Well, if a source dvd had always a bitrate of 8000kbps then it wouldn't make any difference turning off or on DACB. But to be honest I have many doubts that there is such a DVD.

You are confused about what DACB does, it only chooses an average bitrate independently for each cell so that overall reduction of all cells are proportional to the original ones.

If you had disabled before DACB then the calculated average bitrate needed to do the overall reduction would be used for all cells, which isn't the best method.

About CCE or any encoder doing all the work, it is always doing what is supposed to do, DVD-RB passes a maximum, an average and a minimum bitrate, the encoder then will try to do what it was told.

[cmsoliveira]

Hi,

only to complement onesoul post, let's say you have a low motion scene, an high motion scene, an another low motion scene.

With DACB off

Low motion -> 4000 kbps
High motion -> 4000 kbps
Low motion -> 4000 kbps

The bitrate is equal on all cells;

With DACB on

Low motion -> 3000 kbps
High motion -> 7000 kbps
Low motion -> 2000 kbps

DACB assigns bitrate were is more needed (in this case the high motion scene). So it makes perfect sense that this option is always on.

@Jdobbs: DVD-RB keeps getting better and better... Thanks for all the hard work in making this amazing tool :)

[Msc_Alex]

Originally posted by cmsoliveira
With DACB off

Low motion -> 4000 kbps
High motion -> 4000 kbps
Low motion -> 4000 kbps

The bitrate is equal on all cells;

With DACB on

Low motion -> 3000 kbps
High motion -> 7000 kbps
Low motion -> 2000 kbps



No, we were talking about CBR movie's with DACB on it would still be 4000 for all motion scene's.

And yes there are lots of CBR movies, it's not the best way i know, a lot of the first disney dvd's are. I like to use RB with dvd's I made from standalone recordings. Thats great with maestro, you can make a dvd of 12 Gig and drop it in to RB for the perfect reduction :)

[cmsoliveira]

And yes there are lots of CBR movies, it's not the best way i know, a lot of the first disney dvd's are.

Interesting. I didn't know that, because i never encountered a dvd with CBR (but i don't have any disney dvd's).

Even so, the fact that DACB is on doesn't affect nothing. It will, most probably, assign the same bitrate for all segments, just like you said.

[jdobbs]

If you have a CBR movie -- that sucks. So why would you want to make it suck again in the output.

VBR is always better for a DVD. So DVD-RB encodes at VBR.

If you had a CBR source it would probably assign the same average bitrate for all segments -- but a VBR average bitrate, which would then be distributed. In other words you would get the same thing as if you didn't have DACB on... so what would be accomplished by having it as an option? The output for DACB will always be as good or better than non-DACB.

But its a moot point. After several hundred test DVDs -- I have not found one single CBR source. I think you are mistaken about the Disney sources.

Why wouldn't you author your own using VBR? I realize you could set the bitrate to the max... but that makes it the same as you'd get in VBR on the difficult parts, and way more than you can use on the simple parts...

[Msc_Alex]

This one i still had on my HD, ok bitrateviewer could be wrong
but it shows as a flatline in maestro:
http://img172.exs.cx/img172/2126/aliceinwonderland1ob.th.gif (http://img172.exs.cx/my.php?loc=img172&image=aliceinwonderland1ob.gif)
Alice in wonderland, pal r2 (maybe thats why)

I don't use cbr (just in menu's), but on some dvd's the source m2v are from a standalone recorder (just one pass;) )

[jdobbs]

Hmm... is this a commercial DVD -- it's also interlaced, which is strange.