How to upload to YouTube a video not taken by the iPhone4

Hello,

I have the iPhone4 (Verizon). I can/have taken video with this phone and uploaded them to YouTube easily.

However, I can't seem to use my phone to upload to Youtube a video not recorded by my phone.

I have successfully taken a video with my digital camera - formated it to MP4 on my computer and transfered to it iPhone via USB cable. My iPhone will play this video perfectly. There doesn't seem to be anyway to upload it to YouTube from the iPhone's Photo app nor anyway to attach it to my gmail and email it to YouTube.

Is there a way to upload a movie NOT taken by the iPhone4 but on the iPhone4 to YouTube?