Save volume only on TV Player exit (optimize DB usage)

[angela.schmid@…]

Saving the volume to the DB on each volume change is unnecessary. To optimize DB usage, the patch saves the volume only on exit of the TV Player (TV::PrepareToExitPlayer?).

There was also a small bug: On each volume change in the TV Player the volume is saved twice when software volume is configured:

In libs/libmyth/audio/volumebase.cpp VolumeBase::SetCurrentVolume?

• Calls UpdateVolume?, which calls SetSWVolume, when software volume is configured it saves
• the save in SetCurrentVolume? itself

[Jean-Yves Avenard <jyavenard@…>]

In 85baf66840dbf728af732f1d346ffe63fbe3ab41/mythtv:

Save volume only on TV Player exit

Original patch by angelaschmid <angela.schmid@…>. Thank you

Fixes #12144

[Roger Siddons <rsiddons@…>]

In 26e44bf08cf2f3b17a3eae7efa8afa65156d7fe0/mythtv:

Revert "Save volume only on TV Player exit"

This reverts commit 85baf66840dbf728af732f1d346ffe63fbe3ab41.

AudioPlayer? exits/resets in numerous other places (for example: livetv, end-of-recording dialog, audio stream change)
so catching all of them is difficult and error-prone. An alternative solution will be used.

Refs #12144

[Roger Siddons <rsiddons@…>]

In 874b65bc84bd080ec538d27a12573b2e582ffaef/mythtv:

Audio: Fix duplicate Db writes of volume for software mixer

When using software mixer volume updates were being written to Db twice

Refs #12144

[Lawrence Rust <lvr@…>]

In abaf8ddb8ca4f9cc1196a08ca9593498398f948f/mythtv:

Audio: Offload dbase updates when volume is changed

VolumeBase::SetCurrentVolume? writes the new volume immediately to the dbase.
This dbase update occurs on the main UI thread and can take several mS
on a remote FE. The delay caused by a series of volume changes (e.g. by
holding down the volume up/down button) can adversely affect video playback,
causing minor loss of a/v sync which results in the player dropping frames
which in turn is distracting to the viewer.

This patch delegates volume dbase updates to a separate thread which
also adds a holdoff period in order to reduce the number of updates.

LVR 0.27/0234
Fixes #12144

Signed-off-by: Roger Siddons <rsiddons@…>