Hi Jeff, I had exactly the same problem when I started putting videos on you tube .the picture was good but the sound wasn't great. Having done a massive amount of research there really are very few mobiles or video cameras even at high prices that record good audio. You have the facility to record either mp3 or wav on the SX900 on the audio record facility.
As has already been mentioned record whilst you are playing and then I always first go to a good program for trimming your audio Audacity is free and great for this.
The reason I say is trimming is because obviously it takes a few seconds to sit at the keyboard and press record and the same to stop. You don't want a long gap either end.
Then when you upload your actual video footage I am presuming you are using video editing software..again there are many free programs out there although they often have limits on how much you can upload , watermarks etc. I personally purchased the VSDC video and sound suite for a year and was approx £18 for the year and worth every penny spent.
You then upload your video into the program and you can add the sound and then with patience and a little cutting and splicing line up.the sound with the video . It can be a little tricky to start but you then get wav quality sound with your video and makes such a difference.
I am no technical wizard but gradually have got quite comfortable putting the sound with videos and then of course you can start adding pictures, text even video clips moving backgrounds and effects with your videos. All depends how far you want to go but for £18 a year plus a decent camera stand with which to take the videos with a good stable mobile attachment the sky's the limit.
I hope this has helped in some way .. best wishes from David another SX900 owner
