5DIII firmware update 30th Oct 2013
 

Apparently if you have an external monitor connected you can circumvent the 29 minute cutoff plus new mirroring feature allows HDMI out alongside using your rear LCD screen

OliviaTech Canon 5D Mark III Firmware Update Features and Improvements

Canon U.S.A. : EOS 5D Mark III Firmware Update

Re: 5DIII firmware update 30th Oct 2013
 

Peter, unless they changed something specific for this, it's not quite how you think….

I have the Ninja II, and yes you can record longer than 29 mins using the HDMI out, but that's not quite the same thing as unattended recording.

The problem is that if you don't touch anything on the 5D3 body for 30 mins then it automatically flips out of live view mode, even though you have sleep set to "never".

It doesn't go to sleep, but it's no longer in live view mode….

I'm running 1.2.1. Now if they changed this in 1.2.3 let me know, but there was no mention of it in the release notes.

I can keep the 5D3 alive by hitting the 'rate' button periodically (I knew there had to be a use for this button!), because it's seen as a live person attending the camera so it doesn't shut off, but doesn't actually 'do' anything else while recording video. Using this workaround I've recorded to the Ninja II from the 5D3 HDMI for 90 mins non stop and got a ProRes 422 file in to the bargain :).