We now should wait for libvpx integration

Ref #3630

Ref #3630

This patch implements art display in the default skin, in the same way as it is
implemented in qt4 interface, namely if no video is available, art is displayed in lieu of video.

This patch gives skins developpers the possibility to display the art file
 associated to the current input in an image control.

It features the following :
    - a new 'art' boolean parameter is added for the Image control (skin.dtd)
    - when set to true, the skin engine will reuse this control to display
      the current art file
    - in addition to 'scale' and 'mosaic', the resize parameter can now accept
      a new 'scale2' value, that respects the original aspect ratio of art files

If, for instance, video is not embedded and visible="vlc.hasVout" is used
for a video control, the video control background was not refreshed.
Yet, partial redraw (overlapping windows) could occur, leading to a visual artefact.

The black borders are removed by modifying the width of the window.
It also fixes the behavior of zoom when used in fullscreen.

Untested

Close #3621
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

For some reasons, only Qt/Win32 is affected.
Close #3612

Close #3627

Close #3622

Close #3607

Fix parsing to get trailertype. Should help to view all the trailers now.

libavcodec doesn't allow multiple threads on some codecs, so blacklist them
to have only 1. Not sure if it would be easier just to revert few commits to
default whole to 1 thread.

I did't spot any other codecs that would exit if thread_count > 1 in libavcodec.

Fix #3613

add demux=avformat and play-and-pause, remove play-and-stop as it's
playlist-option not item. demux=avformat seems to help littlebit on
constant seeking (we don't want to dos as http-access closes and starts
new connection on seek currently ).

It closes #3512.

It is needed to be sure that the first image displayed after a discontinuity
(flush or seek) is the right one.