h263 vs mpeg quantization

[plugh]

I'm encoding higher resolution material (for example 1280x544@24fps 2.35:1 film), targeting a specific hardware / software playback target - ie xbox/xbmc using mplayer/libavcodec.

Two questions re: quantization type

1) Will switching from h263 quantization to 'standard' mpeg matrix incur much (any?) additional decoding cpu load with that target decoder?

2) Given that resolution and, lets say, a target bitrate of ~5Mbps, should I stick with h263 quantization? Mpeg matrix is recommended for 'high' bitrate, but I'm not sure this qualifies given the resolution - 4 times the typical 640x272 'SD' encode.

I've got tweaked xvid 'HD' encodes playing well on that platform at the moment using h263 quant, I'm trying to decide whether to invest time/effort re-characterizing using mpeg matrix.

I note that all but one of the dxn hardware profiles (including their 'High Def' profile) require use of h263 - is it because it requires less target cpu resources? Significantly higher bitrates? Or is it simply to make life simpler for chip makers?

Any 'gotchas' with relatively recent mplayer/libavcodec code and non-h263 quantization?

Thanks!

[Manao]

1) It may ( marginally ) : h263 dequantization can be optimized a bit more. It would represent nothing more than 1-2 % of the decoding time however.

2) Use the quantization / matrix that pleases your eyes most. We really can't decide for you.

[plugh]

Just a followup, for future reference...

In my test piece, there were two noticable effects from using mpeg matrix vs h263 quant.

1) Keyframes were significantly larger.

2) Just about every time there was a scene change (ie one of the large keyframes) the target system would increment its 'late frame' counter. Seems the added processing wasn't quite enough to cause a frame drop on my target, but was enough to trigger the counter.

I guess the dxn folk had reasons for requiring h263 in their hardware profiles.