Certain file types can be read and played back while still recording. Some of the slowmo instant replay threads on the old forum showed this. I believe .ts and .mxf files work as long as the editing program supports it and renders to a new file.
We should gather all the slow motion and instant replay links and info in the following thread.
A new thread on implementing edit while ingest with a proper client for that should probably have its own thread as that isn’t exactly simple video playout. The tech should be fairly similar to the instant replay stuff just with a different client and an output file.