It's easy to take and edit quick videos on the iPhone, but getting great audio isn't always as simple as pointing and shooting. The iPhone microphone isn't too shabby at close distances, but when you're trying to film in a crowded room, it's not quite enough. Here are a few of my favorite ways to avoid tinny or terrible sound when shooting iPhone video.
Get closer to your subject when in a noisy environment
One of the biggest audio mistakes beginning videographers make is trying to film someone speaking from across a room when there's no way to clearly hear their audio. Background noise, room echoes, and outdoor sounds can all contribute to poor quality here. Instead, if you can't use an external microphone, try getting closer to your subject. Your shot may be a little more zoomed in than you'd like, but your audio will be crisper.
Use another iOS device
Of course, you don't have to get close to your subject when using an external microphone. If you have an older iPhone or iPod touch, or you can borrow a friend's, you can use it as a portable microphone with little problem. Use your iPhone to film how you'd like, then set up the second iPhone near where you want audio. (If you're filming interview-style, you can even hold it like a portable microphone or hide it, mic-side-up, in a jacket breast pocket.)
To record, just open the Voice Memos app on the second iPhone and dictate what clip you're shooting ("Christmas party, kids playing with new toys"). Then set your video camera to record, and clap your hands in front of the frame — it's an old trick, but a good one.
When you finish shooting, you'll have the video and a separate audio track; you can bring both into iMovie on the Mac and edit accordingly.
Buy an external microphone
If you're trying to shoot something a little more high-quality, chances are you'll want to pony up a little cash for an external microphone. There are a few different categories here: on-device mics, wired lavalier mics, and wireless microphones.
There are a bunch of on-device mics available for your iPhone or iPad, depending on what you plan to record. I've personally heard good things about Photojojo's Mighty Mic ($70), Blue's Mikey Digital ($100), and the Zoom iQ6 ($100); the first is designed for shooting on the go, while the latter two are more for single-room recordings and music captures.
In the wired lavalier section, you've got the Movo PM10 ($22) as a cheap but well-reviewed option, and the Rode smartLav+ ($78).
If you have professional wireless lavalier and portable microphones you own, you can hook them up to your iPhone, but you'll need to pair them with a 3.5mm adapter first.
Those are some of my tips and recommendations; anyone have a setup or tips they like to get good audio when shooting on the iPhone 6? Put 'em in the comments.