Generic camera properties

[joshdoe]

Currently most camera sources expose little to no camera attributes through the GObject property interface, the recently merged pylonsrc having the most properties exposed. However because cameras can have so many different attributes, it can become unwieldy to expose them all through the GObject property interface, plus dynamic properties can't be added to a GObject.

Perhaps common attributes could be added as static properties, but then a camera-attributes property could be added which itself is a GObject dynamically populated with camera attributes. There could also be a simple API created to set camera attributes via a C interface. GenApi itself could be used, generalized across all plugins.

Unfortunately either dynamic property approach doesn't work well with gst-launch, so perhaps there could also be a property that contains a semi-colon delimited list of Feature=Value pairs.

Any and all suggestions invited.

[mrstecklo]

Implemented setting all features in pylonsrc with PylonFeaturePersistenceLoad() and config-file property in my flags2 branch. Haven't tested it yet as COVID keeps me away from my cameras now. I'll test it in a couple of weeks. It is based on my other pull request, so it is kind of suspended now.
I've also added possibility to ignore default values for features with ignore-defaults property

[thiesmoeller]

@mrstecklo : for pylonsrc you could always test with the emulated cameras of Basler pylon

to enable them just set PYLON_CAMEMU in your environment
export PYLON_CAMEMU=5
will create e.g. five emulated cameras to be usable by any pylon application in this environment