Becareful that it adds a delay of one frame, so it needs to be
flushed on discontinuity and it will return NULL one time.

 It is not yet used, but it will be needed for filter that need to delay
frames.

We now test that the selected fourcc actually works by calling vaGetImage.
Initial patch from Gwenole Beauchesne.

No functional changes.

No functional changes.

Two new functions added:

 * val = libvlc_audio_get_delay( p_mi )
 * libvlc_audio_set_delay( p_mi, i_delay )

The delay is measured in microseconds.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

As suggested by Jan Janak <jan@ryngle.com>

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

Entity encoding was missing (for options) in generation of an xspf playlist.
On the reading side the entity decoding is all fine.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

This reverts commit f5b8b43a.

This reverts commit 8c1d2b3e.

 - add an optional display callback,
 - make unlock callback optional (planes could be static),
 - pass an opaque picture identifier from lock to unlock and display
   callbacks (this would enable multiple pictures later),
 - pass pixel planes back to the unlock callback for convenience,
 - use pointer VLC variables instead of configuration strings,
 - fix an unlikely memory leak.

avcodec native decoder has priority over libvpx one, and I don't know
howto change that easily. Fix #3820

Fixes eg youtube viewing.

The signal handler currently does nothing anyway, so this was a waste.