AirPlay was one of the most nebulous topics up for discussion today at Steve Jobs’ special press event regarding iOS, iPods, iTunes and Apple TV. In many ways, it’s something we already know a lot about, since it’s the successor to AirTunes. In others, it’s a mystery.

AirTunes, for those who didn’t know, was the technology that allowed iTunes users who also owned AirPort Expresses to to speakers connected to the portable routers. It was good, but you had to pay $99 for every AirPort Express, and connect them either with optical audio or mini stereo cables to your sound system or receiver.

Now, AirPlay will provide the ability to , which will include offerings from Denon and JBL, among others. Along with music, AirPlay will also stream track and artist information, including album artwork, either over a wired ethernet connection or wirelessly using Wi-Fi.

That’s not all AirPlay is good for. It’ll also allow you to stream video and audio content from your iPad, iPhone or iPod touch running iOS 4.2 when that drops in November. You’ll be able to stream your content from those devices to the Apple TV, for one, as Steve demoed today during the press event.

Here’s where things get murky: Will you be able to stream content to your iPhone, iPod touch or iPad from other sources, like your computer? Jobs cleverly eluded any mention of such a feat, which makes me suspect that the streaming magic is one-way only. That’s troubling news, especially when Google’s acquisition of Simplify Media means such a feature is likely on the way for Android devices.

Many might also wonder why Apple doesn’t just put to use an existing open standard for media streaming, like, say DLNA, that’s already got the backing of many hardware manufacturers. My guess? DLNA has received some major hate, and not without reason. Apple might want to sidestep that debate altogether, and at the same time retain tight control over which hardware partners they work with. AirPlay is less about freeing your music and video and more about a controlled expansion of the iTunes ecosystem.

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