A video player using FFmpeg, which began as an example for the Spout SDK, has evolved as a useful player with transparency for both Spout and NDI output, overcoming the lack of transparency support for the Openframeworks video library at the expense of seeking speed.
The project is hosted as an FFmpeg branch of “Spout Video Player” and the latest release can be downloaded from here.
FFmpeg is required and instructions for download and install are documented in the release download.