One of my favorite features of iOS 4.2 (and later) and the second-generation Apple TV is that if I've taken photos or video with my iPhone, I can use Apple's AirPlay technology to stream those bits of media directly from my iPhone to the Apple TV—I don't have to first sync the media to iTunes or iPhoto. This makes it easy to, for example, show my mother-in-law the video I took of my daughter's first "solo" bike ride at the park.
Notice I didn't say "quickly show." If you've ever streamed iPhone-captured video to an Apple TV using AirPlay, you know the process can be quite slow. (If only there was a word for "as slow as you can imagine while still actually progressing.") Video files are huge to begin with, the video on your iPhone hasn't been compressed, and wireless networks present additional bandwidth challenges—the end result is that it can take five or ten minutes for the Apple TV to buffer a two-minute iPhone-filmed video. (And the Apple TV decides on its own when it's received enough video to allow playback to begin.)
As I discovered over the weekend, when I attempted to show the aforementioned bike-ride video, this makes for a less-than-impressive demo. (Cut to scene of me telling the family, "Go ahead and do what you were doing; I'll let you know when it's ready.") But what I also realized this past weekend is that there's a way—with a few limitations—to "queue up" these videos for instant playback.
The latest Apple TV doesn't have a hard drive, but it does have 8GB of internal memory. Some of that memory is used to store the Apple TV's operating system and other software, but a big chunk of it is used to cache media—video, audio, or photos—for better performance. If you've ever streamed a movie from your Mac or from Netflix, you've seen the blue progress bar "fill up" as the Apple TV stores a chunk of that content (a technique often called buffering). When you're watching the video, the Apple TV actually reads the stored data, rather than the data streaming over the network; as stored data is used, it's discarded and replaced by new data. This is why you (usually) don't see stutters and freezes in streamed video, even with a choppy network connection.
But this caching doesn't just happen with media streamed over the Internet or from your Mac—it also happens when streaming, say, video from an iPhone. And, in fact, that video stays in the Apple TV's cache until the memory is needed for something else.
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