[Libva] Ivy bridge PRM and H.264 encoder implementation

[Joe Bloggsian]

It is great that intel have released proper documentation for the Ivy 
bridge GPU/media engines. Kudos to them; if only all silicon vendors 
were so progressive!

In particular it is very interesting to see the detailed information on 
the VME engine in Vol4 Part2, which seems a much more sophisticated 
piece of hardware than I expected.

Comparing the documentation to the even the staging branch of 
intel-driver (in particular inter_frame.asm). It *appears* that there 
are significant hardware features that the current encoder 
implementation might not be using (or could be used better). A couple of 
examples:

1) The search and cost centers of the current implementation appear to 
always be zero. It seems to me this will firstly be resulting in 
improper costings for the motion vector selection (mv cost should be 
relative to an approximation of the predicted motion vectors). Secondly 
it implies a limitation of max MV that can be found to 16  x, 12 y 
integer pixels from the origin (not nearly enough for HD video). This 
seems consistent with the poor MV selection I see in the encoded video. 
It should be easy (and far better) to set the search and cost centers to 
(one of the) MVs found in the macroblock to the left as this is on the 
whole going to be a much better approximation of the predicted MVs, and 
this would also allow the encoder to find long MVs. One can imagine 
other even better ways to set the search position.

2)  It appears that none of the early exit options are used; 
EarlySkipSuccess, IMESuccess, EarlyIMEStop, SkipSuccess, etc. These 
ought to be a "free" significant performance gain just for setting some 
registers?

Does the above seem reasonable and are there any existing plans to 
implement these kinds of improvements?
If not already being worked on - would it be interesting for me to 
attempt to make changes similar to those I described and provide patches?

Cheers,
Bloggsian