As promised here is the how to video guide, along with a quick demo. Yes My headphones are lime green, I know.
Back on subject, you’ll notice in the video that the Red HDMI cable is plugged in and working at the same time as the usb-composite adapter (Canon AVC-400ST is the proper name). Since both ports stay on while recording (note the flashing red light), you can monitor audio from one port and video from the other. On a Side note, the video output only works on one or the other. So if you’re using the HDMI port you wont get video out of the yellow composite connect, only audio will be output through the Red and White connector. And if you’re using the yellow composite connect for video, then you wont get any video out of your HDMI port.
One other very important thing to remind you all of is that this solution only works if you’re using an external field monitor. The screen on the back of your camera WILL TURN OFF as soon as you plug in the adapter. If you don’t have a field monitor then give my Dirt Cheap monitor project a try or pick yourself up a nice HDMI ready Lilliput 7″ 669gl monitor.
If the Connection demonstration at the beginning of the video isn’t straightforward enough for you to follow let me know and I can post a diagram. There are also a number of other headphone amplifiers available for more and less then the FiiO E5. If you go with one of them, make sure it has a good way to control the volume level. Some of the cheaper models don’t have any controls at all.
I’ve also received a number questions about the usb-composite adapter cable. As far as I know this cable comes with every new Canon DSLR so be sure to check your box before you start tossing things in the trash. A replacement for this cable is $25, so it’s probably not something you want to loose.
Update: Filips pointed out in the comment section that this fix only works if you are using Magic Lantern. He is absolutely correct. If you have the 5D mark II or t2i you are good to go but if you’re using a 7D then no dice. The 60d is in the works but the Magic Lantern firmware update is still a beta version.