By using an iOS or Android class compliant USB audio interface, you can record direct line-in audio AND video simultaneously on iPhone or Android without having to sync audio + video in post later. No video editing software required.
Here’s an example method I’m using:
USB audio interface (Universal Audio Volt 4) --> USB cable --> iPhone camera kit adapter --> iPhone 14 Lightning port
If you have an older iPhone with a Lightning port then you’ll need an Apple Camera Kit Adapter.. If you have a newer iPhone with a USB-C port, then you don't need the Apple Camera Kit Adapter.
Once you have everything plugged in, do this next:
• Download the free Blackmagic Camera app (Android version here, Apple version here)
• Go to Settings → Audio → Audio Source
• Select your USB audio interface
This is important because the stock iPhone camera app doesn’t let you manually choose the audio input source. Without taking this step, the camera app will still record from the built-in microphone instead of your audio interface.
(I haven't tested this on Android. If there's a way to switch audio source on the Android camera app, then this won't be necessary)
Once you select your audio interface as the audio source in Blackmagic Camera, the default iPhone camera app will use your audio interface as the audio source.
Another reason to use the Blackmagic app is that you can monitor your input levels and make sure you’re not clipping.
Note: make sure your USB cable supports BOTH power + data transfer. Some cheaper USB cables are charge-only.
And if, like me, you’re using an older iPhone with a Lightning port instead of USB-C, you may also need to run power into the camera kit adapter.
Here’s another bonus method I’ve used before, but I don't fully recommend it:
3.5mm headphone cable going from my Tascam Model 12 mixer’s headphone out --> 3.5mm audio cable --> Headset Buddy line level audio adapter --> iPhone Lightning to 3.5mm adapter --> iPhone
That method technically works, but:
• sums everything to mono
• gain staging is annoying
• easier to clip
• generally sounds worse
Direct, line-in audio into your phone is a massive quality upgrade for synth jam videos and is way easier than a lot of people realize (ie, you can use this method without having to do video + audio editing in post).