What shows on 4th device with HDHR Prime?

I have HDHomerun Prime 3 with Channels Plus.
HDHR has 3 tuners, but what happens to the 4th device that runs the Channels app?
Does any of the first 3 device lose streaming?

No. If all tuners are in use, and an additional tuner is requested, then the client trying to access a stream gets an error. I believe for live viewing on a client, the error is something like "Tuner not responding" or "Tuner not available". For the DVR, if a program is scheduled to start recording but there are no free tuners, then an error is recorded in the log indicating that the system could not tune the channel because there were no free tuners.

Conflict resolution is one area that Channels definitely needs work, as it doesn't really have any. For instance, the priority of passes is only consulted when the DVR starts a recording; if there are no free tuners, it does not check to see if the program about to start has a higher priority and stop the lower priority recording. Also, if you are watching a live program and a recording is due to start on a different channel, the system does not inform you and allow you to give up your live tuner to allow the recording to proceed; it will just fail in the background.

Part of the reason for this is that originally Channels did not have a DVR, and each client handled access to the tuners on their own. In this situation, there was no way for individual clients to know what other clients were doing, or which tuners were available. When the DVR was introduced, the default behavior of the clients remained the same; clients are only aware of the tuners in use by the DVR for recording, but not about live viewing. (This default behavior can be changed if you enable "tuner sharing" on the client; then all connections are run through the DVR. However, this is not the default.)

Thank you, but what would happen in this scenario with tuner sharing on? It would help only when trying to access a tuner that's already being used to record or watch the same channel, and only that same channel, right?

And if the user also has TVE access to the same channel, then that could also be the "fourth tuner", yes?

No, TVE sources do not use HDHR tuners. One user has reported having 16 concurrent TVE streams going.

And yes, tuner sharing only has a benefit for streams requesting the same channel. Each cable/OTA stream still needs its own tuner. But, if you want to have a sporting event on multiple screens (say for Super Bowl), then tuner sharing would only use a single tuner; if you did not enable tuner sharing, each screen (and the DVR if you are also recording the game) would each have a separate tuner in use.