Produces a split-screen output from two video inputs:
- video: one frame is used for the top half of the output.
- video2: one frame is used for the bottom half of the output.
If only one stream is connected, the other half is filled with black. Output is a single stream (one split-screen frame per call).
Scope currently passes only the primary stream as video. To use two physical streams, Scope would need to support a second input (e.g. a second track) and pass it as video2 to the pipeline.