[airtunes] - reset coverart and metadata when starting an airtunes stream - fixes showing stale metadata from previous stream.
Merge pull request #5209 from qaweizoux/airplay_mirroring_fixes

[Fix] Stale metadata/cover art when using airplay audio mirroring
videodb: fix GetMusicVideoAlbumsNav() in combination with masterlocks (fixes #15385)
videoplayer: adapt lateness detection and dropping to buffering
video player: present correct pts to user for a/v sync (after buffering in renderer)
videoplayer: some rework and documentation
renderer: bump buffers to 5
videoplayer: update frametime, it might change due to fps detection
videoplayer: give streams with invalid fps a chance for fps detection
dvdplayer: allow rewinding at end of stream, do a seek after rewind
dvdplayer: observe pts counter overflow
dvdplayer: avoid short screen flicker caused by unnecessary reconfigure of renderer
vdpau: advanced settings for auto deinterlacing
player: fix rewind
OMXPlayer: some caching fixes for pvr
fix incorrect display of fps when dr kicks in
ActiveAE: slightly reduce buffer size
Revert "vdpau: comment some features that will be added later"

This reverts commit e00b4f65864d623ab4d2e9e5c06db138e661f1cf.
ffmpeg demuxer: faster channel change for PVR addons without internal demuxing
(such as MediaPortal, ArgusTV, MythTV, NextPVR)
Credits: FernetMenta, Davilla, Popcornmix, Whaupt
ffmpeg demuxer: make sure we start mpegts video with an i-frame