Question on the video functions of Canon SLRs

[Sean Setters]

Canon SLRs do not autofocus while recording video. Several Nikon SLRs have the feature, but we've yet to see it in Canon's.

EDIT: It looks like I was incorrect. Reading up on Canon's Learning Center, I found:

AF modes are:

Quick Mode AF:
By far the fastest and most positive option for AF, especially in low-light situations, or with subjects that don’t have a lot of detail. It’s the only AF mode for video that uses the camera’s 9-point AF system and dedicated AF sensor. However, it does require interrupting live viewing to perform, and it cannot be used at all during actual recording.

Live Mode AF:
This AF method reads focus off the imaging sensor, so there’s no interruption of live viewing. It’s not as rapid and positive as Quick Mode AF, but in a pinch, it can be used during actual recording — although it’s best-used to pre-focus before recording begins. Live Mode AF cannot focus-track moving subjects.

Live Face Detect AF:
This method is similar to Live Mode AF, but is able to recognize human faces in a scene, and will target the nearest (or largest) face it detects to focus upon. If no faces are visible, it reverts to Live Mode, with a central white rectangle as its focus target (this can be moved around most of the picture area if desired). Again, it cannot focus-track moving subjects. Unlike when shooting still images, there is no AI Servo AF capability.

AF is always activated on the EOS 5D Mark II with the rear AF-ON button. Pressing half-way down on the shutter button will not engage AF, unlike some other EOS models.

Hmm....So basically, there is autofocus, but no tracking. So, really, the autofocus isn't terribly useful if it cannot track subjects. It's just as easy to prefocus before recording.