Constant Q and Target Bitrate

[Somewhat Damaged]

I am encoding for a PMP device and would like to use a constant quantifier of 2, however I have a max bitrate of 2.5mps. Is there a way to limit the high end of the bitrate for constant q?

[Sharktooth]

no, it's not possible or better... it's a nonsense.

[Somewhat Damaged]

Thank you Shark Tooth, I was pretty sure you couldn't however I had hoped for some type of custom matrix or something. Two pass target bitrate it is then...:D

[foxyshadis]

no, it's not possible or better... it's a nonsense.

What's nonsense about constant quant that gets raised to accept a bitrate cieling? MPEG-2 encoders do it all the time, they have to.

You just have to set your level settings appropriately; I don't know if you want custom or not, for 2.5Mbps and no resolution restriction you'll probably need to ask Celtic_Druid for a custom profile. If xvid can't do it in cq mode, then use one-pass abr with some insane bitrate, with min-quant 2, and level restrictions for approximately the same behavior.

[Teegedeck]

It certainly would be news to me if MPEG-2 encoders respected max bitrate without changing the base quantizer or AQ. How should that work?

[manono]

I think you misunderstood foxyshadis, Teegedeck. She was saying that in CQ or OPV MPEG-2 encodes, like with CCE, the quant can get raised to take into account the max bitrate. And by extension, it's not too much to expect a profile for XviD that does the same thing, as Somewhat Damaged was requesting.

[Teegedeck]

I am encoding for a PMP device and would like to use a constant quantifier of 2[...]
What's nonsense about constant quant that gets raised to accept a bitrate cieling?
The confusion seems to be one between const. quant. and constant quality. A constant quantizer cannot be raised, otherwise it wouldn't be constant. We had some discussion here (http://forum.doom9.org/showthread.php?t=114811) about how a new constant quality mode in XviD could be implemented that wouldn't simply mean constant quantizer.

[GodofaGap]

A constant quantizer cannot be raised
I think this is getting a bit to semantical. :)

It seems the OP is requesting an encoding mode that always uses a certain QP, unless the bitrate rises over a certain kbps value (in which case the QP must be raised). This has nothing much to do with constant quality.

[Teegedeck]

:) Well, yes. That was theorizing. And as XviD's const. quant. mode is very semantical, I think foxyshadis' practical suggestion of going CBR at an insane bitrate is the best solution.

[Sharktooth]

Constant QP of 2 is ... constant QP of 2... if QP gets rised during the encoding, well, it is no longer "constant"...
Also rate control doesnt play any role in Constant QP so i cant see how you can limit the "bitrate" in the actual implementation.
Limiting the bitrate in a non-bitrate based mode is simply a non-sense.
A more practical approach would be a 1pass ABR mode or a Nth pass mode with max bitrate cap.
For future xvid dev a CRF mode wont be that bad...