[MPlayer-dev-eng] key frame extractor / vo_jpeg use YV12 instead of RGB patch

[Trent Piepho]

On Thu, 15 Mar 2007, Andreas Krebs wrote:
> this is how far I got, however this already created some interesting results, so vo_jpeg
> now runs almost twice as fast on my PC, simply to the fact the it now directly uses
> YV12 rather than converting to RGB and back, also  the image quality seems to have
> improved a bit by this (at least the resulting jpegs look better to me - but maybe it's
> only my imagination ;-) ).

It's much better to do it this way, sending YUV to libjpeg rather than converting
to RGB and then having libjpeg convert back to YUV.

You are not doing it quite right though.  The YUV data in video formats is
almost never full range, but has something called ccir r.601 excursions.
JFIF standard jpegs on the other had have full-range yuv data.  So, you
must convert one to the other if you want to create standard jpeg files.