Creating alpha channels for VIP

Glad to know that you have found solutions to the problem.

Just one thing to note, If the alpha stream is separated from the video stream using Color Plane Sequencer, and sent to a consumer block, e.g. Alpha Mixer, a FIFO buffer (and probably Timing Adapter to convert between ready latency 1 and 0) is needed at the alpha path to avoid deadlock. The Chroma Key probably does not need this because it already has a build-in output FIFO. A depth of 8 or 16 pixels should do the job.