This fixes crashes that could occur while processing Qt events during a
source's destruction.

Originally the processEvents code was added to make sure that any window
messages being sent to the browsers were being processed by Qt.
However, that was only necessary for browser panels as they are actually
associated with windows/views.  Browser sources are OCR, thus they do
not need this.

Cuda appears to be a bit buggy and can result in corruption where as
it's not being seen with other hardware decoders.  Remove cuda for now
as a hardware decoder to prevent the possibility of corruption.

rtmp-services: Update GameTips.TV

Fixes a bug where hardware frames would not transfer to RAM for the last
few frames of a video.  The 'ret' variable can be 0 even though there
are still frames ready.

Bicubic/Lanczos Shader Improvements

deps/media-playback: Use hardware decoding with non-alpha WebM files

When "custom FPS" is disabled, ensures that OBS and the browser always
use the same FPS even if the user changes it in settings.

Fixes same issue as 5c04876d, but reverts that and changes it so that
external_begin_frame_enabled is not used instead, which seems to fix
that issue.

There are 6 mixers, so we want 0x3F for 6 bits, not 0xF which is only 4
bits.

B-frames on sandy/ivy bridge do not work, so disable for those
platforms.

On 3770, when many (5+) browser sources/panels are active at once,
browsers started freezing.  It is apparently due to this particular
issue:

https://bitbucket.org/chromiumembedded/cef/issues/2483/osr-invalidate-does-not-generate-frame

The solution is to remove the "WasHidden(true)" call.

This fixes a race condition where the audio/video backends/threads may
start using sources before their obs_source_info::create function has
been called.

This function is not used outside of the source file, so make it static.

When a source type has been removed (i.e. its plugin has been removed)
info can be null, which is permitted.

- Fix: Ensure (1, 1) coordinate gets clamped.
- Fix: Increase weight precision by premultiplying UV in VS.
- Cleanup: Group coordinates 012/345 instead of 024/135.
- Cleanup: Remove unnecessary branches.

NVIDIA RTX 2080 Ti, Intel GPA, SetStablePowerState

256x224 -> 1323x1080: 123 us -> 123 us

Also increase weight precision by premultiplying UV in VS.

Intel HD Graphics 530, Intel GPA, SetStablePowerState

256x224 -> 1323x1080: 1221 us -> 1020 us

obs-ffmpeg: Set some parameters for dynamic bitrate in new nvenc

The FAILED() macro is for HRESULT values; NV_FAILED() is what should be
used for NVENCSTATUS.

This forces an I-Frame when reconfiguring encoding parameters so that
the changes apply immediately.

The hardware accelerated decoder context needs to be explicitly unrefed
when it's no longer in use, otherwise it and many resources associated
with it will leak.

When hardware accelerated decoding is enabled, sometimes it can't
initialize for whatever reason, so it will fall back to software on its
own.  When this occurs, it will not use the hardware pixel format on the
frame; instead it will defer to a standard format on the frame.  So if
the frame format does not match the expected format, assume software
decoding.  (This was also what the hw-decode.c FFmpeg example did if the
format did not match the expected format)

Prevents log spam when dynamic bitrate is used

When the streaming audio track was separated from the recording tracks
in advanced output mode in be8c0633, it mistakenly removed the opus
audio encoder code when FTL is used.  This restores that code.

CEF outputs multiple audio streams at once, and OBS was only able to
handle one at a time.  This fixes it by using audio lines for each CEF
audio stream, and mixes them together itself.

Adds the "audio_line" internal source type as a bare source type for the
sole purpose of outputting audio, and the obs_source_info::audio_mix
callback which allows mixing of those audio lines, which is then treated
as normal audio for the source.  Audio line objects should be added as
sub-sources when multiple audio lines from a single source are needed,
then mixed together with the audio_mix callback.

The difference between the new obs_source_info::audio_mix callback and
obs_source_info::audio_render is that obs_source_info::audio_mix (along
with the audio_line source) are only one track, and it outputs audio to
the source automatically via obs_source_output_audio() when the call
completes.  This allows the mixed audio to be treated like a normal
source's audio, in that you can filter it, change its volume, or monitor
it.

This change was necessary because the CEF (used with the browser source)
outputs multiple audio streams at once to a single browser source, so
it's the program's responsibility to mix those streams together itself.

UI: A couple of pause changes

UI: Fix inconsistency with spaces

Adds dynamic bitrate support (marked as beta) to the advanced settings
for now.

The dynamic bitrate operates based upon estimating the current bitrate
output, and then adjusting the bitrate on the fly as necessary when
congestion is detected as a replacement for dropping frames.

This may still need adjustment, as it is difficult to accurately emulate
real-world frame drop scenarios.  This does not currently drop frames at
all, and because of that, very high congestion may cause additional
stream delay to viewers (because data will be buffered), but from
limited testing, most congestion will not cause that and it can safely
recover pretty quickly without adding significant delay.

(This commit also modifies mac-vth264, obs-ffmpeg, obs-qsv11, and
obs-x264)