Explain Bit Allocation

[jriker1]

I usually work with CCE and have to do very little to the bit allocation manually to make sure everything is in the green. In this particular situation that wasn't the case and brought some questions. You have the global bitrate, and the local bitrate for the section you are working with. So let's say I have a 45 minute AVI file and set the global to:

Avg: 2075
Min: 0
Max: 9500

The system says the file will be 683 megs in size. So I'm going forward 10 seconds at a time and find a section in red. I adjust the bitrate for that piece so it's now green. Now the filesize does not change. I would think the average bitrate would adjust to accomodate or at least the filesize change. Does this mean that some other piece of the video has had it's bitrate lowered and may turn red as a result?

If this is the case, this seems like a loosing battle. Wouldn't it make more sense just to up the average and have CCE adjust things as necessary? I thought that manually doing it would provide for a smaller overall final file, however with my question on what happens to the rest of the video if you increase the local bitrate for one area, am unsure.

Any assistance in understanding things would be much appreciated.

One other question, is the conversion done by 2.67 better or worse than 2.70? I sometimes notice that the bit allocation with 2.67 comes out better than 2.70.

Thanks.

JR

[Matthew]

Does this mean that some other piece of the video has had it's bitrate lowered and may turn red as a result?

If this is the case, this seems like a loosing battle. Wouldn't it make more sense just to up the average and have CCE adjust things as necessary?

Yes and IMO yes.

By keeping the global average bitrate constant and adjusting certain sections you are stealing from one part of the video to help another, and second-guessing CCE's bitrate allocation. This could make sense if you have used an unusual bias value, or don't care about the credits, but otherwise I think not.

I use the section post-encode just to get an objective measure of the quality of the output (q values), in particular whether a higher average bitrate is required.

[jriker1]

Thanks for the reply. Perhaps you can answer this. I do a single baseline pass of my AVI file. Do a multipass and set to three passes. When I go to manually alter the bitrate, I am able to get rid of all the red. I run the conversion. Then go back into the bitrate configuration screen after the conversion is done. Everything is al red all over the place.

Is this bitrate allocation working right? When I get rid of red areas and the system adjusts accordingly does it not show the new areas that are now read because of the changes?

JR

[Matthew]

To be honest I don't know, I never do tweaking, I only check post encoding to see if a movie backup can fit on one disc with acceptable quality to me.