[MPlayer-DOCS] More XviD encoding options documented for XML doc

[Jeff Clagg]

On Tue, Jul 05, 2005 at 03:45:24PM +0200, Guillaume POIRIER wrote:
>   <emphasis role="bold">qpel</emphasis>
>     Increases the precision of the motion estimation from halfpel to
>     quarterpel.
>     The idea is to find better motion vectors which will in return
>     reduce bitrate (hence increasing quality).

qpel increases the number of *candidate* mv's, I don't think it makes
sense to say the mv's themselves have increased quality. Or I'm just
being too pendantic.

>     However, quarterpel precision motion vectors are coded in the
>     bitstream with a few bits,

How about: "Motion vectors with quarterpel precision require a few extra
bits to code,"

>     so if the content do not feature
>     enough possibilities to find better motion vectors through
>     <option>qpel</option>, it will in fact hurt compressibility.

How about:
"but the candidate vectors do not always give (much) better results.
Quite often, the codec still spends bits on the extra precision, but
little or no extra quality is gained in return."

>     <option>qpel</option> can be almost double encoding time, and
>     requires as much as 30-60% more processing power to decode.
>     It is not supported by all standalone players.

I thought it was agreed the penalty is usually no more than 25%?

>     This almost always raise PSNR, but significant slows down
>     encoding (and also needs more processing power to decode).

"significantly slows down encoding"

>     <systemitem class="library">XviD</systemitem>'s GMC (which are
>     more sophisticated than DivX's are not supported by all
>     standalone players.

"XviD's GMC is more sophisticated than DivX's, but is not supported by
all standalone players."

My impression was that most standalone players don't support ANY GMC,
but I don't really know firsthand.