[WIP] Fix issues on the sequence player

[Claude]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>[bug] Issues on the sequence player</issue_title>
<issue_description>Describe the bug
A batch of issues I found on the Sequence Player.

To Reproduce

1. Open blank scene
2. With no images loaded we can still move the slider
3. Click on play and there is a QML warning

file:///.../meshroom/ui/qml/Viewer/Viewer2D.qml:1880:17: QML SequencePlayer: Binding loop detected for property "loading":
file:///.../meshroom/ui/qml/Viewer/SequencePlayer.qml:29:5

4. Now load images
5. Even though the "Fetch" button is checked it doesn't fetch anything : you have to either press play or click somewhere on the timeline to start creating the image cache

6. Play images so you fetch all images 7. Now remove all images from the Image Gallery. You can see the slider is not empty 8. Delete the CameraInit that holds images. The slider is empty now. 9. Click on play : it seems like there is an infinite timeline

Desktop (please complete the following and other pertinent information):

• OS: Rocky Linux 9.4 (Blue Onyx)
• Python version: 3.11.14 (main, Dec 9 2025, 19:03:34) [Clang 21.1.4 ]
• Qt/PySide version: 6.8.3
• Meshroom version: branch dev/timelineSliderImprov
• Commit reference: 16a5756

Additional context

[!NOTE]
I'm on the dev/timelineSliderImprov but these issues are still there on develop</issue_description>

Comments on the Issue (you are @claude[agent] in this section)

@Alxiice I could get through some of the issues but not all.

For (2) :

Meshroom/meshroom/ui/qml/Viewer/SequencePlayer.qml

Lines 189 to 190 in 16a5756

	TimelineSlider {
	id: frameSlider

We can add :

enabled: viewer && viewer.cachedFrames.length > 0

It will disable the timeline when we have no images on startup, but doesn't fix (7) & (9).

For the issue (3) we can fix it here :

Meshroom/meshroom/ui/qml/Viewer/SequencePlayer.qml

Lines 239 to 246 in 16a5756

	MaterialToolButton {
	id: fetchButton
	text: MaterialIcons.subscriptions
	ToolTip.text: "Fetch"
	checkable: true
	checked: loading
	}

By setting :

checked: false

For (5)

Meshroom/meshroom/ui/qml/Viewer/SequencePlayer.qml

Lines 82 to 90 in 16a5756

	onPlayingChanged: {
	if (!playing) {
	updateSceneView()
	} else if (playing && (frame + 1 >= frameRange.max + 1)) {
	frame = frameRange.min
	}
	viewer.playback(playing)
	}
	}

We can call updateSceneView() always (not only on pause) so that when we click on play it will select the first frame and play.

And then there are probably remaining missing updates on gallery changes :

• use onRemoveSelectedImagesRequest to trigger updates</comment_new>