aspectRatioChanged signal does not get emitted when the aspect ratio changes

[al2950]

Expected Behavior

When the stream info changes (on receipt of VIDEO_STREAM_STATUS msg) the _ar property in FlightDisplayViewVideo.qml should be updated.

Current Behavior

On app start the _ar property is set to 1.77 (16:9), but because VideoManager::aspectRatioChanged is never triggered, _ar is never updated and so aspect ration calculations in FlightDisplayViewVideo.qml are wrong. I believe this only affects camera tracking functionality.

Steps to Reproduce:

This is not particularly straight forward issue to see without debugging. But if you have a Mavlink camera that can do tracking, you can do the following

1. Under general settings, set the Aspect Ratio to a unrealistic large wide video, eg 5
2. Restart QGC
3. Initialise the tracking outside of the image on the left (ie on the black bars)
4. Note the tracking box is then displayed well within the image (as the aspect ratio calcs are wrong)

System Information

When posting bug reports, include the following information

• Operating System: Windows 11
• QGC Version: 4.4.1
• QGC build: Built from source, with custom firmware plugin
• Flight Controller: PX4
• Autopilot (with version): PX4 1.15.0 RC2