frontend: Refactor and update Audio Mixer

[Warchamp7]

Description

Moves a bunch of logic out of OBSBasic into a central AudioMixer class, refactors a bunch of code to clean up, and adds a pile of new functionality to the mixer.

Adds a new MenuCheckbox widget for having a checkbox toggle inside a QMenu that does not close the menu after clicking.

The primary addition in this PR is a new audio monitoring toggle button in the mixer itself. Other features have also been added such as the ability to show Hidden sources, Inactive sources, adjust how they get sorted, and an easier way to toggle the layout.

PR also depends on #12734 for icon coloring.

Motivation and Context

With the fixes made as part of #12175, it is now far more reasonable for us to expose audio monitoring more directly to users. It is often very desirable to be able to toggle on monitoring for things like Media Sources or some Video Devices such as capture cards.

I elected to also clean up the Audio Mixer code a bunch while working on this feature addition, and add some other additional features and UI adjustments.

There is more that I want to do and clean up still but I'm trying to keep this PR at least moderately reasonable.

How Has This Been Tested?

Tested muting and monitoring on multiple audio sources both via the Mixer dock, the Advanced Audio Properties window, as well as a separate Audio Mixer window utilizing the same widget, to test that things are properly encapsulated and not kept in any local widget state.

Types of changes

• New feature (non-breaking change which adds functionality)
• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[gbdlin]

Small request for this redesign, if it's feasible and easy enough: can you add one more checkbox to the menu to show sources that are inactive, but present on the previewed screen? Of course it only makes sense in the studio mode, but it would be a great help when you need to adjust levels of a source that will become active with next transition, but without having to find it in the list of all available sources.

[Warchamp7]

Small request for this redesign, if it's feasible and easy enough: can you add one more checkbox to the menu to show sources that are inactive, but present on the previewed screen? Of course it only makes sense in the studio mode, but it would be a great help when you need to adjust levels of a source that will become active with next transition, but without having to find it in the list of all available sources.

This was in fact not straightforward but I added it as default behaviour

[nyanpasu64]

This PR causes ugly pixelated rendering of VolumeMeter text on Linux at 125% DPI scale (and probably Windows as well).

I think you're rendering the text off-screen (backgroundCache?) and blitting on-screen. Unfortunately this may not be easily fixable, because Qt 6 lays out widgets in integer virtual pixels (unless you set a rounding policy, which may cause layout errors when changing DPI at runtime), and you don't know how many physical pixels the QImage/Pixmap will appear on-screen due to position-dependent rounding.

Looking at the QPixmap docs, I found https://doc.qt.io/qt-6/qpainter.html#drawing-high-resolution-versions-of-pixmaps-and-images:

High resolution versions of pixmaps have a device pixel ratio value larger than 1 (see QImageReader, QPixmap::devicePixelRatio()). Should it match the value of the underlying QPaintDevice, it is drawn directly onto the device with no additional transformation applied.

One interesting possible strategy is "multiply size by DPI, round to nearest pixel, then set the QPixmap DPR to the screen, then blit to the widget". If you can convince Qt to not scale it at all (haven't tested), you could get exact rendering, possibly with one pixel cut off or missing at the edges :(

Still waiting for Qt to add https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserverEntry/devicePixelContentBoxSize 🦗 VS Code faced a similar problem with their terminal at xtermjs/xterm.js#2662 (comment) and xtermjs/xterm.js#3926

[Warchamp7]

This PR causes ugly pixelated rendering of VolumeMeter text on Linux at 125% DPI scale (and probably Windows as well).

Thanks for catching this. I'm travelling this week but hopefully the fix will be as simple as adjusting the Pixmap size to be

size() * devicePixelRatioF()) instead of just size()

[PatTheMav]

During testing I found that there are two ways to toggle the display of hidden sources: Either via the Options menu or via the hidden source counter.

That itself is a bit of a UX smell, because there should be a single, canonical, way to do this, not multiple ways. But because there are multiple ways, this creates a bidirectional state binding between both of these controls and at least in my tests, toggling the display of hidden sources via the counter label does not also uncheck the checkbox in the "Options" submenu, even though it should.

So either this binding needs to be made truly bidirectional, or the duplication in functionality is resolved.

---

Also the on_actionMixerToolbarMenu_triggered function never seems to run in my tests, even though I get the context menu both by clicking on the "Options" button or right-clicking into the mixer area. How is this menu triggered?

Similarly debugHideControls exists, but doesn't seem to be hooked up to anything?

[Warchamp7]

During testing I found that there are two ways to toggle the display of hidden sources: Either via the Options menu or via the hidden source counter.

That itself is a bit of a UX smell, because there should be a single, canonical, way to do this, not multiple ways. But because there are multiple ways, this creates a bidirectional state binding between both of these controls and at least in my tests, toggling the display of hidden sources via the counter label does not also uncheck the checkbox in the "Options" submenu, even though it should.

So either this binding needs to be made truly bidirectional, or the duplication in functionality is resolved.

Fixed the state getting desynced.

Also the on_actionMixerToolbarMenu_triggered function never seems to run in my tests, even though I get the context menu both by clicking on the "Options" button or right-clicking into the mixer area. How is this menu triggered?

This is a leftover action from before the refactor. Removed it from the main window UI file and the associated function.

Similarly debugHideControls exists, but doesn't seem to be hooked up to anything?

This was a debug method per the name and left in by accident. Removed.

[RytoEX]

Some questions, some nits.

[RytoEX]

Questions about pointers. Technically should update copyrights in new file headers to 2026.

[RytoEX]

LGTM