Add support for experimental add-on filters by bmatherly · Pull Request #1813 · mltframework/shotcut

bmatherly · 2026-04-11T16:57:21Z

This includes a new selection dialog and generated UIs
The --experimental option is required to expose the selection
--experimental is only available when Shotcut is compiled for debug

When --experimental is enabled, the filter selection menu adds a hamburger menu before the search bar with a single action called "Manage Add-on Filters"

This action opens a new Add-on Filter selection dialog which lists ALL available filters in MLT:

The user can select and de-select MLT filters to be added to the main filter selection as Add-on Filters. After the dialog is closed, the main filter selection is updated with the selected (or de-selected) filters

When the user selects an Add-on filter that has been added to a clip, the UI for that add-on is auto-generated and cached in a temporary folder.

The help button (?) opens a non-modal dialog with a detailed view of all the properties for that add-on filter

I find this feature useful for exploring filters - especially the host of OpenFx filters. This has also exposed some opportunities for improving metadata for some MLT filters - which I will submit in different PRs.

Review comments are welcome.

I recommend that we wait until after the April release before we consider merging this.

This includes a new selection dialog and generated UIs The --experimental option is required to expose the selection --experimental is ony available when Shotcut is compiles for debug

bmatherly · 2026-04-11T17:00:11Z

+bool FilterController::ensureAddOnTempDir()
+{
+    if (!m_addOnTempDir.isValid()) {
+        m_addOnTempDir = QTemporaryDir(QDir::tempPath() + "/shotcut-addon-XXXXXX");


A new Temporary directory is created for every Shotcut instance. If someone opens/closes Shotcut a lot, they can accumulate. But this handles the case of regenerating the UI for software updates or multiple versions installed at the same time. It also makes development easy since I don't have to delete the generated files every time I make a change to the code.

bmatherly · 2026-04-11T17:02:55Z

    QmlMetadata *meta = m_attachedModel.getMetadata(m_currentFilterIndex);
    QmlFilter *filter = nullptr;
    if (meta) {
+        if (meta->objectName().startsWith(QStringLiteral("addOn.")) && !ensureAddOnFilterQml(meta)) {


The UI QML for an add-on filter is only generated when absolutely needed - when a user has selected an add-on filter in the UI. If present, the cached version is used. Else, it is generated. So, in many cases, the temporary directory will never be created if the user opens shotcut, but never uses an add-on filter.

bmatherly · 2026-04-11T17:04:18Z

+            Shotcut.Button {
+                id: addOnMenuButton
+
+                visible: enableAddOns


This button only appears when --experimental is passed to Shotcut.

bmatherly · 2026-04-11T17:05:13Z

        QCommandLineOption gpuOption("gpu",
                                     QCoreApplication::translate("main", "Use GPU processing."));
        parser.addOption(gpuOption);
+#ifdef QT_DEBUG


The --experimental option is only available when Shotcut is compiled for debug.

bmatherly · 2026-04-11T17:05:51Z

+        if (experimental)
+            ::qputenv("MLT_REPOSITORY_DENY", "libmltqt:libmltglaxnimate");
+        else
+            ::qputenv("MLT_REPOSITORY_DENY", "libmltqt:libmltglaxnimate:libmltopenfx");


The experimental option also enables openfx to be loaded at startup.

bmatherly · 2026-04-11T17:06:41Z

+    return settings.value("filter/addOnServices").toStringList();
+}
+
+void ShotcutSettings::setAddOnFilterServices(const QStringList &services)


When the user selects add-on services in the dialog, they are saved in the settings so they can be reloaded very time shotcut starts (only with --experimental)

Copilot

Pull request overview

Adds an experimental add-on filter workflow (debug builds only) that lets users opt-in to exposing arbitrary MLT filter services in Shotcut’s filter menu, with auto-generated parameter UIs and a metadata/help viewer.

Changes:

Add --experimental (debug-only) flag and wire it into MLT repository deny-list behavior (e.g., OpenFX availability).
Add add-on filter management UI: hamburger menu entry in the filter menu + a new “Manage Add-on Filters” dialog backed by a new AddOnServiceModel persisted via settings.
Generate and cache QML UIs for enabled add-on filter services on demand, plus a non-modal metadata/help viewer.

Reviewed changes

Copilot reviewed 25 out of 25 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/settings.h	Adds settings API for persisted add-on filter service list.
src/settings.cpp	Implements persisted add-on filter service list getters/setters.
src/qmltypes/qmlutilities.cpp	Registers new QML type used for the add-on menu popup.
src/qmltypes/qmlfiltermenu.h	Declares C++ QML-facing menu helper for add-on actions.
src/qmltypes/qmlfiltermenu.cpp	Implements popup menu that opens the add-on manager dialog.
src/qmltypes/qmlapplication.h	Exposes `showAddOnFiltersDialog()` to QML/C++ menu helper.
src/qmltypes/qmlapplication.cpp	Implements dialog launch for add-on filter management.
src/qml/views/filter/filterview.qml	Plumbs generated-UI help signal up to the dock for display.
src/qml/views/filter/FilterMenu.qml	Adds the experimental hamburger menu button.
src/models/addonservicemodel.h	New model for enumerating MLT filter services and enabled selections.
src/models/addonservicemodel.cpp	Implements MLT filter discovery + persistence of enabled add-ons.
src/mltcontroller.cpp	Adjusts `MLT_REPOSITORY_DENY` based on experimental flag.
src/mainwindow.cpp	Threads add-on service model into `FiltersDock` construction.
src/main.cpp	Adds debug-only `--experimental` option and sets app property.
src/docks/filtersdock.h	Adds support for showing non-modal add-on metadata help dialog.
src/docks/filtersdock.cpp	Wires QML signal to a `QTextBrowser` help dialog; sets `enableAddOns` context property.
src/dialogs/addonfiltersdialog.h	Declares add-on filter management dialog.
src/dialogs/addonfiltersdialog.cpp	Implements searchable, checkable list of all MLT filter services.
src/controllers/filtercontroller.h	Adds add-on UI generation/caching members and add-on metadata loading hooks.
src/controllers/filtercontroller.cpp	Implements add-on metadata insertion/removal and on-demand generated UI caching.
src/controllers/addonqmlgenerator.h	Declares generator for add-on filter parameter UI QML.
src/controllers/addonqmlgenerator.cpp	Generates parameter UI QML + metadata help text for add-on services.
src/controllers/addonmetadataparser.h	Declares parser to normalize MLT metadata into descriptors.
src/controllers/addonmetadataparser.cpp	Implements metadata parsing into generator-friendly descriptors.
src/CMakeLists.txt	Adds new sources (model, dialogs, generator, parser, QML type helper) to build.

Comments suppressed due to low confidence (1)

src/docks/filtersdock.cpp:53

The addOnServiceModel parameter is not used in this constructor, which can trigger unused-parameter warnings (and it’s unclear why it is being threaded through MainWindow). Either use it (e.g., expose it to QML via a context property) or remove it from the constructor signature/call sites; if it must remain, mark it with Q_UNUSED(addOnServiceModel) to make the intent explicit.

FiltersDock::FiltersDock(MetadataModel *metadataModel,
                         AddOnServiceModel *addOnServiceModel,
                         AttachedFiltersModel *attachedModel,
                         MotionTrackerModel *motionTrackerModel,
                         SubtitlesModel *subtitlesModel,
                         QWidget *parent)

Include all the metadata fields

ddennedy · 2026-04-13T22:37:15Z

Thank you; it is nice to have. The first filter I tried avfilter.rotate crashed (Windows). Not looked into it yet but a reminder this is full of landmines. I think we should filter out the ones that already have an installed QML if not too much trouble.

ddennedy · 2026-04-14T19:15:10Z

avfilter.rotate crashed

I found that the avformat module was incorrect about metadata and pushed a change. Now, it does not crash.

bmatherly · 2026-04-15T02:00:56Z

I think we should filter out the ones that already have an installed QML if not too much trouble.

I am on the fence about this. On the one hand, it would reduce redundancy. On the other hand, filters can be exposed/represented in many ways. Maybe we are exposing a service through our curated UI, but not exposing some of the parameters or doing it in a limited way. It might be good if the experimenter can work with the raw filter even if we have exposed it through our supported filters.

As a reference, the following services are used in multiple Shotcut filters:

autofade (2)
brightness (4)
channelcopy (2)
frei0r.alpha0ps (2)
frei0r.IIRblur (3)
ladspa.1204 (2)
lift_gamma_gain (2)
mask_start (5)
movit.opacity (2)
panner (2)
qtcrop (2)
qtext (2)
volume (4)

As a variation on this comment, for each add-on filter, I could add a note somewhere to indicate which supported filters are using that MLT filter. Perhaps as a column in the manager dialog. Or maybe a tool tip in the generated UI.

ddennedy · 2026-04-15T02:09:32Z

I am on the fence about this.

OK I see your point.

Use LineEditClear Replace hamburger menu with "configure" button

Add support for experimental add-on filters

cb259b3

This includes a new selection dialog and generated UIs The --experimental option is required to expose the selection --experimental is ony available when Shotcut is compiles for debug

bmatherly commented Apr 11, 2026

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bmatherly requested a review from Copilot April 11, 2026 17:09

Copilot started reviewing on behalf of bmatherly April 11, 2026 17:09 View session

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ddennedy force-pushed the master branch from f7d5b05 to 704e3c8 Compare April 12, 2026 05:13

bmatherly added 2 commits April 12, 2026 19:41

Resolve review comments

3883602

Refactor addon filter help dialog

a4e539d

Include all the metadata fields

bmatherly force-pushed the autogen_filters branch from a4657e5 to a4e539d Compare April 13, 2026 02:17

ddennedy reviewed Apr 13, 2026

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Comment thread src/dialogs/addonfiltersdialog.cpp

ddennedy reviewed Apr 13, 2026

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Comment thread src/qml/views/filter/FilterMenu.qml Outdated

bmatherly and others added 2 commits April 14, 2026 21:41

Resovle review comments

1f516da

Use LineEditClear Replace hamburger menu with "configure" button

Move 720p video modes to Other

3c1a910

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ddennedy commented Apr 13, 2026

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ddennedy commented Apr 14, 2026

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bmatherly commented Apr 15, 2026

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bmatherly Apr 11, 2026 •

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