If you have a 5D Mk II you may already know about the Magic Lantern firmware hack that adds a bunch of features that really help cinematographers. One key feature is the ability to turn off the Automatic Gain Control on the audio which can result in better audio as well as on-screen audio meters.
The folks at Magic Lantern have released some videos showing that they have video recording working on the EOS 50D which has never had native video recording before. Of course, since the 50D doesn’t have a microphone you will need to use an external audio recorder such as a Zoom H4 or similar device and then syncing the audio and video in post production. While this may sound like a pain, dual-device recording is actually the industry standard for best quality audio.
While the Magic Lantern Firmware isn’t officially released for the 50D yet, it looks like it is almost ready so you 50D owners out there that have wanted to get into video, now is the perfect time to go find a good audio recorder and get ready for some DSLR Video love coming your way soon.
However, if you have a 5D Mk II, 550D, 600D, or 60D you might want to head over and check it out.
Magic Lantern Wiki: http://magiclantern.wikia.com/wiki/Magic_Lantern_Firmware_Wiki