Close #6451

Usage: http://localhost:8080/art?item=1234

The slider is not displayed, anyway. But sometimes it flickers through
for a short moment which does not look good.

based on patch by Richard Grenville <pyxlcy@gmail.com>

Note that the origin values can also be negative when we have our window
on a secondary screen.

This fixes playback on an AES-128 encrypted stream I ran into: the key
URL happened to have "iv" somewhere in it, which led VLC to try - and
fail - to parse an IV.
Signed-off-by: Hugo Beauzée-Luyssen <beauze.h@gmail.com>

Coeffs have been recomputed.

Close #6132

There is not that much common code left for the access case, except for
debug messages. The resulting code is a lot easier to read IMHO.
Also I have no way to test the access plugin, so lets split it where it
will not get more broken.

They are mostly used by plugin descriptors.