A musical reader is anxious to perform to a remote audience and writes:
I know you’re a musician and I’m hoping you can answer this one for me. My family lives across the country and I’d like to perform a concert for them via the Internet. I have a MIDI keyboard and play through Apple’s Mainstage 3. Is there some way I can stream my performance to them?
There is. I’ve tried this using a couple of different setups and the one I’ve settled on is Rogue Amoeba’s $59 Nicecast. The gist is that Nicecast allows you to use any app as an audio source and stream its output over a local network or the Internet. Specifically, here’s what you’d do.
Download a copy of Nicecast. (If you’re a starving musician you should know that the trial works perfectly for 60 minutes before the audio intentionally degrades, so you can try it out before you decide to buy.) Launch Nicecast and click the Source button. In the pane that appears click on Select, choose Select Application, and navigate to Mainstage. It should launch. (If it doesn’t, launch it yourself and then choose it from the Select pop-up menu you just clicked on.)

Nicecast is a nice way to stream your Mac’s audio.
Now click the Share button. In the resulting pane you’ll see the addresses for your stream—one for the Internet and another for your local network. Click the Copy button to copy the Internet address to the Mac’s clipboard. Paste that address into an email or text message (or Tweet or Facebook post or whatever) that you then share with your family so they know how to tune into your stream. (They can do this via a Web browser or, if they’re Mac users, they can launch QuickTime Player, choose File > Open Location, and then add the address to the resulting field and click Open.) You’ll want to coordinate the time of your performance with your audience so they know when to tune in.
When it’s time to start, just click on the Start Broadcast button and begin banging the keys. You’ll know that Nicecast is receiving Maintage’s output when you see the Level meter light up. You should be able to hear your playing as you normally do—likely through headphones or speakers attached to your Mac. Depending on the speed of your connection, people tuning into your performance will hear it begin a few seconds later.

You may need to open port 8000 on your router.
A word of caution: You may need to configure your router so that Nicecast can do its job. Specifically, you may have to open up port 8000, which is how Nicecast gets ’er done. If you have an AirPort base station, the process goes like this:
Launch AirPort Utility, click on the base station attached to your broadband modem, and click Edit. Click on the Network tab in the resulting pane and in the Port Settings area click the plus (+) button. In the sheet that scrolls down enter a description in the same-named field (Nicecast has a nice ring to it) and enter 8000 in the Public TCP Ports and Private TCP Ports fields. In the Private IP Address field enter the IP address of the Mac that you’ll be streaming from. (You’ll find the IP address in System Preferences’ Sharing preference.) Click Save and then click Update to configure the base station with these new settings.