The recording time left timer was being called an unnecessary time,
in the stats constructor, when it should have only been started
when the recording starts.

A previous refactoring to make DrawMatrix unnecessary has left behind
unreachable YUV conversions. Even if this code was somehow reachable,
DrawMatrix for YUV -> RGB doesn't exist anymore, so they would render
incorrectly anyway.

Minor cleanup

Variable was never used. Clean up both C++ and shader code.

Incoming texture is UNORM, so the value must already be saturated.

Lambda replacement was added, but old function was left behind.

Shuts down browser panels early to ensure that cookie data doesn't
necessarily get lost.

UI: Remove 5 file limit for drag & drop

(This commit also modifies the UI, obs-ffmpeg, and obs-output modules)

Fixes a long-time regression where the program would lock up if an
encode call fails.  Shuts down all outputs associated with the failing
encoder and displays an error message to the user.

Ideally, it would be best if a more detailed error could be displayed to
the user about the nature of the error, though the primary problem is
the encoder errors are typically not something the user would be able to
understand.  The current message is a bit of a generic error message;
improvement is welcome.

Another suggestion is to try to have the encoder restart seamlessly,
though it would take a significant amount of work to be able to make it
do something like that properly, and it sort of assumes that encoder
failures are sporadic, which may not necessarily be the case with some
hardware encoders on some systems.  It may be better just to use another
encoder in that case.  For now, seamless restart is ruled out.

UI: Dark theme consistency for Scenes vs Sources

- Selected but unfocused Source colour
- Scenes font
- Padding when editing Source name

UI: Fix hotkey theme issues

UI: Add hover color to hotkey icons

libobs/UI: Add Transition Previews

This commit adds a preview to the properties window for transitions.

The preview will play back the transition at the global transition
duration or the transitions fixed duration, between two private scenes
with an A and B label, and different background colors.

This commit adds a function to forcefully stop a transition, and to
increment/decrement the showing counter for a source with the MAIN_VIEW
type.

These functions are needed for the transition previews to work as
intended.

Closes obsproject/obs-studio#1639

Fix VAAPI CBR

libobs: UI: Remove Qt usage from graphics thread

libobs: Restore casts to fix Clang warnings

obs-outputs: Fix undefined MSG_NOSIGNAL

This fixes Xcode warning about detecting UI usage from another thread.

Define MSG_NOSIGNAL even if CRYPTO is not defined.

Clang doesn't like it if you convert T** to const T* const* without
casting even though it should be safe. Might be a C language thing.

Avoid sigpipe on writing to closed file descriptors

obs-frontend-api: Add method to trigger a Studio Mode transition

obs-qsv: Fix QSV failing with new DCH drivers

obs-frontend-api: Add methods to get/set transition duration

This patch fixes QSV failing with new DCH graphics drivers. QSV is not
initializing under certain conditions when the graphics adapter 0 is not
set to iGFX due to outdated MSDK dispatcher. Updating to MSDK with new
dispatcher to enable proper initialization of QSV encoder with DCH
drivers.

This can happen when trying to write to a closed socket (in the case
of an RTMP server closing the connection).

This could happen if writing to a socket which was closed by the peer.

libobs: libobs-d3d11: Fix alpha blend