Just ahead of Lumia Denim and Lumia Camera 5 arriving for the likes of the 930, 1520 and 830, Microsoft has pushed out a necessary companion application. I have to say that I'd thought that the 'moments' functionality (from short video bursts) was going to be baked into LC5, but it seems that it's a standalone app that's, presumably, called upon from LC5. Anyway, screens and links below.

From the Store description (it states that Denim is needed, but it'll work on any captured 1080p and above video, on the supported phones, it seems):

With Lumia Moments you can extract great action shots from your videos or 4K Moment shots on your Lumia (or full HD shots on the Lumia 830).

Use Best Frame to find pictures and save them as Living Images, then see them brought to life in the camera roll or Lumia Storyteller. Action Shot lets you add a strobe effect to show action or add blur to emphasise motion.

Lumia Moments is available for Lumia 830, Lumia 930, Lumia Icon and Lumia 1520 as part of the Lumia Denim update. 

The idea is simple enough, pick a supported high resolution video and then frame grab as needed using a streamlined interface (or indeed composite multi-frame action shots). Here's Lumia Moments on my 830:

The two main options, of which 'Best Frame' is the obvious to look at. The idea is that something's happening (e.g. at an event or with kids or pets), you take a long press-burst of video on the shutter key and then later on you pick out the perfect full resolution photo/frame.

After the initial loading, the timeline scrubbing tool works quickly and well - it's easy to select the frame you need, following which there's a second or two of processing while the full resolution (2MP or 8MP) image is calculated, and the option to save to the Camera Roll.

The end result was indeed 2MP images, as expected (i.e. much more than simple screenshots, which is often how other OS and devices implement frame grabbing). On the 930 and 1520, 4K video will result in full 8MP images, which is pretty impressive.

In terms of performance, loading up the video in the first place on the 830 took around ten seconds, I'd imagine similar performance for 4K video on the 930 etc. While this might seem on the slow side, remember that frame grabbing from MP4 video is extremely complex because of the way individual frames are built up from parts of the previous master frame and then incremental changes - so there's a LOT of calculation going on.

Results are good, though obviously it's all tuned for use with Lumia Camera 5, which I don't have on any of my devices at the time of writing (Friday evening), I'll put up more examples in due course.

In the meantime, grab Lumia Moments from the Windows Phone Store, have a play if your device/OS version is compatible and please report back.