We try to do our best to have the video frames scaled the best way
to fill most space on the final frames, keeping aspect ratio. The user
can later on rescale or move the sources as usual but it makes the
default behaviour a better and more natural especially now that we
set default restriction caps to the video tracks.
And fix the unit test to take that change into account
Basically we were advertising that the source size would be the
size of the track if it hadn't been defined by end user, but since
we started to let scaling happen in the compositor, this is not true
as the source size is now the natural size of the underlying video
stream.
Remove the unit test and reimplemented using a validate scenario which
make the test much simpler to read :=)
The GstFramePositioner might be finalized before the notify callback
Without this commit,
gst-editing-services / ges_basic / test_ges_timeline_remove_track
can reproduce the case.
Now subclassing a ghostpad with an alpha property so that
we can multiply the alpha of the frame positioning meta
and the alpha of that pad, setting it on the compositor pad.
https://bugzilla.gnome.org/show_bug.cgi?id=797169
Otherwise if frame positionner is disposed after track element has been
finalized, it will raise a critical message because we will try to
disconnect a signal handler on a freed track element object.
https://bugzilla.gnome.org/show_bug.cgi?id=766525
