Short answer: Final Cut Pro.
Explanation: Before getting the Roland Go mixer I would, for example, record myself playing piano on the iPhone video app (with the iPhone built in mic, for reference). Simultaneously, I would be recording the audio separately in the DAW. Then I'd load the iPhone audio/video track and the DAW audio track into Final Cut Pro and slide the tracks into sync, then muting the iPhone audio of course. Hope that makes sense.