I have produced an HEVC (H.265) elementary stream which contains alpha (produced from Apple VideoToolbox framework), from which I would like to extract the alpha channel for further processing.
I'd like to process the alpha in either one of these two ways:-
(a) A series of grayscale PNG/JPEG images, with the alpha channel of each frame
or
(b) A series of PNGs with alpha with the RGB and Alpha composited in a single, semi-transparent image
How can I achieve either of these with FFmpeg/GStreamer?