I think you are oversimplifying some things and are mistaken about some others. You make it sound like a trivial feature to add, but if that was the case it would have been added when Live View first came out. Obviously, there are some complications. Processing speed is certainly one. I would bet good money that the D90 is limited to 720P because of processing speed.
I would agree. I would also say that processing speed is, by far, the primary difficulty.
Another significant issue is the sensor. The image from the sensor on the D90 is polled over a relatively long period of time. For rapid motion, the subject can move visibly during the polling. The result is a "jello" motion. I haven't seen it, but people online are complaining about it. We won't know whether Canon has overcome this issue with the 5D until we have more real-world reports.
Exactly - as I'll follow up on later in this message.
As for auto-focus and auto-exposure, the 5DM2 does both during video. The auto-focus is via contrast detection, so it is pretty slow. Of course, that's how most video cameras work already, so it isn't really a step backward for shooting video unless you have a video camera that supplements with an external autofocus system.
The auto-exposure of the 5D is still a bit confusing to me. From what I can tell, getting it to auto-expose is easy. Getting it to lock exposure is a bit more work. The shutter speed is fixed at 1/60 or 1/125 (which is probably all you would want for 99% of 30P shooting). You can control the aperture while shooting and let the camera set the ISO, or you can do the reverse.
This is the first I've heard of it doing these features. This is part of the problem, Nikon with the D90 and Canon with the 5D2 are releasing incomplete information, which is frustrating when they're hyping the video feature as hard as they are. As far as I can tell, both companies are completely mute about such basic things as focus and exposure.
If you don't think that the D90 and 5DM2 are amazing, you should spend some time on some serious video forums. People are practically wetting themselves with excitement. On the other hand, they are infuriated by the small but critical limitations of these products.
Well, I think they're being sold a false bill of goods. See my mention above - the companies are being extremely vague about just what their video features can and cannot do. Consumers are being sold this as if you can throw away your camcorder, but the reality is far different. Heck, you couldn't even record Illuminations with one of these!
Amazing cameras? Perhaps. Amazing camorders? Debatable. Amazing on a technical level? I'm not convinced. Please don't misunderstand me - I'm talking
purely about the video recording on a technical level. Nothing else.
On a purely technical level, I find the D90's video feature to be no more impressive than the K20D's 21fps capture, and that was announced almost a year ago. Nikon just went a different route - instead of 21 separate photos per second, they give you more lower-resolution photos per second with more compression and with a basic microphone. Without knowing the tech specs of either, I suspect that either camera could have the same functionality as the other, but obviously outputting separate pictures requres writing a lot more data, so you will fill the buffer much faster.
The 5DM2 costs almost 3x as much as the D90, and it offers higher resolution but possibly the same limitations. I'm not sure how this is so technically amazing. We're still talking about cameras with 14.6 or 12mp outputting <2mp video or one with 21mp outputting just over 2mp video. Even if it adds AF and AE, those are features that are pretty common in LV nowadays. The lack of more processing power (and speed to write to the card) is the only reason why they couldn't capture even higher resolutions.
Again, I believe the only technical differences between these cameras and any others that have Live View functionality is the processing speed and presence of a microphone. All it takes is grabbing the Live View picture at a lower resolution and dumping it to a memory card quickly enough. Heck, Sony's DSLRs could probably beat out most any others at video due to their faster-than-the-rest contrast-detection AF and in-body IS. But, they forgot to put in a microphone, so...