Your iPhone already comes with everything you need to capture great video. You will have better audio captures with a decent microphone though. The ZealSound Bluetooth Lavalier Microphone for iPhone helps you capture your interviews, podcasts, and presentations in better quality.
This smart Lavalier mic is compatible with a variety of iPhone and Android smartphones. It has an MFI certified chipset and lasts up to 6 hours on battery. It can capture audio in 48kHz quality and allows for real-time monitoring. The SmartMike+ app gives you control over various recording parameters.[where to get it]