I have mine set this way: Press share button once to take screenshot. Double tap it to begin recording. Hold to bring up share menu as well as saving the last 15 minutes of gameplay. I'm still not sure if that's how it works when it comes to saving past 15 minutes. But I think you can only save past 15 minutes if you bring up the share menu by holding the button. Otherwise you're just beginning a recording from when you double tap or single press depending on which control scheme you use.
There's mics on the camera, one in the controller, and the mono headset mic plugged into the controller. Which mics are being used for online multiplayer? I'm always hearing someone's microphone in AC4: Black Flag and am wondering if maybe they don't know which device is recording as well.