Having a pattern which notably changes in time makes it clearer that
sources keep playing even when they are not active.
# The following pipeline works
PIPELINE = """
videotestsrc pattern=0 ! selector.
# The following pipeline works
PIPELINE = """
videotestsrc pattern=0 ! selector.
-videotestsrc pattern=13 ! selector.
+videotestsrc pattern=18 background-color=4294901760 ! selector.
input-selector name=selector ! autovideosink
"""
input-selector name=selector ! autovideosink
"""