Does anyone have experience with motion blur added in post? How credible is it?

[Jason Mackey]

I've always stuck with the 180 degree shutter rule and compensated with a variable ND.  I just acquired a BMPCC and learned about the need for an IR cut filter to boot, so it seems I'll now need 2 filters for any shots involving daylight - unless I can crank up the shutter angle and do away with ND altogether?

I know motion blur added in post was used for the three Hobbit movies:

 

...which was a pulldown from 48fps.  Does anyone else here have any experience using plugins (or paid version of DaVinci Resolve) to add in motion blur?  I image there is some sort of tradeoff between the IQ and color of the image sans ND filter and funky looking motion cadence.  The scenes in the trailer above (at least the ones with just actors moving around and not the CGI stuff) seems "normal" to me, but I've only been shooting video for a few years, so I may not yet have a critical eye for it.

[dbp]

I think it's alot like Twixtor, depends on the scene and background.

I've used RealSmart Motion Blur, and it's hit or miss. Sometimes it works great. Other times, if it's a limb passing in front of a complicated background, there can be funky artifacts.

At least with motion blur, as opposed to Twixtor, the artifacts are less noticeable because they occur so quickly. 

I would never depend on it as opposed to a proper ND filter, but it can work in a pinch. 

[Hans Punk]

Reelsmart motion blur can help take most of the sharp choppy shutter artifacts away when using a higher shutter speed to reduce exposure. Like any image analysis that uses optical flow or similar interpolation algorithm - it can only be pushed so much before it will introduce its own edge artefacts. Knowing how to refine the settings in the plugin will give best results.

I often shoot higher shutter speeds when I know that post stabilisation of handheld footage is going to be applied - the sharper frames enable a more accurate stabilisation solve to be made. Then I apply post motion blur to take the quality of motion a step closer to the appearance of a 1/50 shutter. It does not always need a heavy touch, just taking the edge off the sharp frames can help make the footage appear much better, and is far less prone to reveal nasty artifacts.

 

here is a rough before/after example:

 

Password: birds

 

[BasiliskFilm]

Couple of thoughts. Smoothly moving objects on simple backgrounds should be fine. Super fast action with overlapping motion, or lots of particles of fragments, and you might have problems with images "tearing"
Also remember that this is processor intensive stuff. A fast new machine with 1080 footage might be fine for a few short clips, but you wouldn't want to do a whole movie at 4K with an old machine.
If you have any shots where you are adding visual effects or shooting on green screen, then there are good reasons for shooting sharp and adding motion blurring to your final composited image

[M Carter]

I get a lot of drone footage from clients. And the drone guys don't seem to have a clue about frame rates and shutter speeds, I get lots of 60p and even, like, 40p stuff. So generally I have to retime it all. I usually use Timewarp in AE and the blur looks pretty legit; but these are aerial landscapes and so on. If you really examine the blur from Timewarp, you can see it's more of a "replicated pixels" thing than a true blur, but I doubt the average viewer would notice. And it does apply blur naturally, not just globally. Really takes the drone stuff to a higher level and allows me to retime and even do keyframed retiming. (In AE, you really have to remember to label the frame rate on the raw footage before you drop it into the comp - say it's 60p and your comp is 24p. Make sure you check the footage info - like, shift-command G or similar - and enter the framerate of 60p before you drop in the comp, or you'll get flicker.)

If you're doing important scenes and shooting very crisp for keying or stabilizing, I'd say, shoot a take at the correct speed and decide which works best.

I never shoot "wrong" shutter speed for stabilizing though - as long as I get decent marks in the frame, the software is moving the whole frame, motion blurs and all - the only reason I could see to shoot at a higher shutter speed would be if tracking marks were getting blurred. 

[ThomHaig]

Reelsmart Motion Blur can be pretty handy. I typically work in motion graphics, and it's a common tool for 3d artists (where motion blur can take ages to render out of 3d) - and the plugin is marketed to be used in both footage and motion graphics. I've always seen is as a compositing aid really, and it's got me out of some tight spots and helped achieve a more realistic looking composite a handful of times. I'd never consider Reelsmart MB as a replacement to in-camera motion blur though. I can see how that pipeline makes sense in a green-screen heavy project like the Hobbitses where compositors will want a pretty hard edge key on the green screen to avoid spill, and then MB can be added in post to blend everything together. If it's not a green screen project, I'd just base your shutter speed on the amount of MB you want: It's a hassle to do it in post, and you'll be looking at some long render times.

[Jason Mackey]

Thanks everyone.  My biggest takeaway from all of these replies is that it can work in a pinch but I shouldn't be the basis for every shot.  I'll stick with NDs.

[BasiliskFilm]

Another time it might be useful to do in post is if you are speed ramping clips shot at high frame rates. If you shoot at 120 fps, you are going to have quite a fast shutter speed, so when you play back at actual speed in a 24fps timeline, it will look quite juddery 
You can use MB software to simulate a 180 degree shutter in these situations.