Yea what Don said.
You need to have an audio "In" on your video recording device for the best audio quality. The Kodak Zi8 has that and can record in 1080. Connecting the line outs from the keyboard to a camera audio input gives a richer, fuller, true sound. I love Dave's videos, and even his awesome live performances would be enhanced with a similar setup.
It can be done with an android cell phone but you need a special cable to connect to the headphone jack for recording. A dedicated camera with an audio in is the way to go.
Ebay has Zi8's for sale and cheap. Canon also makes video cameras with a "mic in". That's what you want to be looking for "mic in" /"audio in"
Another way is to record your performance with your cell phone camera, with the line "out" from the keyboard to a PC line "in". And record both simultaneously, and then later sync audio and video with a video edit program.
You have different options, but having great audio is just as important as the video quality, especially in music videos.
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Larry "Hawk"
♫ 🎹🎹 ♫ SX-900