broadcast.go & broadcast: use specified broadcast start & end time to schedule "on" & "off" actions

[Saxon Milton]

So far we have immediately performed “on” actions (actions to be performed to start hardware), but this doesn’t make sense if the broadcast start time is later than when we actually create the broadcast. It’s proposed we add a mechanism in the goLive routine (or similar) to wait for the start time and then switch on the devices, and then wait for the end time and switch off the hardware.

[Saxon Milton]

It’s proposed that a timer will be added to the broadcast/youtube.go goLive routine to wait until the start time to begin the transitioning process. In addition, two signal channels will be returned from BroadcastStream to allow for external actions to be performed when it’s time to start the transition (i.e. turn on hardware), and also when it’s time to end the stream.

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[Saxon Milton]

Alternatively, callback functions could be provided to the youtube.Broadcast function to be used for starting and shutting down hardware.

[Saxon Milton]

Resolved by PR #141.