I would like to test these changes some more days until you commit this pull request, only to be sure it runs some days without problems. But it was working great for me in Ubuntu.

Default Values should be:
stretch height: 0%
stretch width: 0%

then values between 0% and 240% are possible and trigger scaling.

Made some screens again:
http://www.imgbox.de/users/public/images/Ng6dlHSZoD.png

Maybe somebody could check "src/ui/glw/glw_video_common.c", the if/else structure.
This was needed this way, because it frezzes if there occur multiple rescalings in time for me.

Bit like it is now it is working without problems until now, and as long as value stays 0 or the proportional zoom is used, nothing happens at all andgoes over.

OK, for me it is working without problems with Ubuntu as well as on PS3.
Watched full movie on PS3, and let play movies with full 240% stretched width and height, as well as shrinked to 30% / 22% and let it run for half an our, and streched quickly using the sliders, no problems to report, working as expected.