When a new device is selected, a best-possible frame rate is chosen
for the initial configuration of the device. This has to be set in the
source settings, as those are the "source of truth" for the properties
and the device configuration.
The object has to be created explicitly first before setting the
frame rate value. The source then has to be updated explicitly as well
to ensure that the change will be picked up by the next iteration
of the render thread to "tick" the source and thus make it configure
a capture session with the fallback framerate set.
When a capture card or video capture source is contained in the scene
collection's list of sources, but the source is not a part of any
scene, it will be first created but then destroyed again in a deferred
fashion (as it has no strong references to it anymore).
This will happen before the capture source has finished its own
initialization, hence why the source pointer can be invalid at that
point.
Some devices will report different framerate ranges for formats that
are identical apart from color primaries. Without taking these into
account, only framerates for one color primary variant would be used
to populate the framerate dropdown in the property view of the camera
source.
Checking for a difference in color primaries when iterating over all
available formats for a device thus requires checking for this
variation and adding the additional frame rate range as well.
Some devices do not support all color formats at all resolutions, but
the capture card source automatically uses an available color format
and compares it against the available format for a specific resolution.
Without being able to change this format, some resolutions do not
work as CMIO will not be able to find a compatible format. Thus the
color format needs to be manually selected for capture card sources
as well.
PatTheMav
jcm
Anton Kesy
Sebastian Beckmann