What are best practises to make your film/video shots future proof?
How can you repurpose your video shots for multiple different applications such as traditional interlaced
broadcast, web broadcast, or film production, and do it without introducing significant judder, blur, or
Web broadcasting is gradually changing how videographers select their mode of capture - often to 24p or 30p frame rates determined by imposed limits of 30 frames/second on many video sites in order to save some network bandwidth. While these limits are imposed to reduce costs, it is arguable that capturing video at lower frame rates is a mistake, and that higher frame rates should be used, preferably double the rate, with high quality frame rate conversion (FRC) to rates appropriate for web publishing.
At lower frame rates, if frame-to-frame motion is too extreme, it may be very difficult or impossible to automatically motion-interpolate intermediate frames in order to achieve good results, particularly if they need to be viewed frame-by-frame. All other things being equal, all (repeat ALL) frame rate converters do a better job with higher input frame rates. Other things that influence FRC quality are noise, and lossy video compression.
A higher image capture rate can include deinterlaced field rates for professional quality interlaced cameras.
For example, 30ifr (interlaced frames) per second is actually 60 fields per second (60i), so the effective
scene sampling rate is 60, and can be regarded as equivalent to 60p, but only if used with a very high
quality deinterlacer. Viarte deinterlaces from 30ifr
to 60p and 25ifr to 50p using novel algorithms so that the result is virtually indistinguishable from
capturing progressive at 60p and 50p. By this we mean that there is no resolution loss, no residual flicker,
and no perceptible residual combing. If you have interlaced video cameras, it is actually better to continue
to use them, than to purchase cameras that only work at lower frame rates such as 30p, 25p, or
24p, where FRC is more difficult in general.
If you do decide to replace a high quality interlaced camera with a progressive one, then very, very seriously consider only going from 30ifr to 60p, or 25ifr to 50p. Then you can frame rate convert using a high quality converter to anything you need, whether it is finally converted to interlaced or left as progressive.
So you capture this 60p sequence, and it looks nice and smooth, even with a small shutter angle (fast
shutter). Say it uses 180 degrees, i.e. the shutter is open half the time. At 1/60 of a second between frames, this represents a shutter exposure of
1/60 * 180/360 = 1/120 of a second. Now you decide to frame rate convert it to 24p. At 1/24 of a second,
the effective shutter angle is 360 x (1/120 / 1/24) = 72 degrees. As any videographer will tell you, this
is much too fast for film, and will result in considerable motion judder in a daylight scene with lots of detail.
In general, we usually need to add accurate motion blur as we go from a higher frame rate to a lower frame rate.
To avoid this problem, isovideo provides a configurable/tunable accurate motion blur facility in our Viarte frame rate converter and Viarte server. It can add precise motion blur, so the 72 degrees from the example above can be extended to 180 degrees by adding 108 degrees. While not trivial to do, adding motion blur again comes down to having good frame rate conversion, and a fair amount of compute power, but its attainable.
When downsampling frame rates by larger amounts, adding the correct degree of high quality motion blur to avoid motion judder is a necessity, not a luxury! For example, going from 60p/50p down to 30p/25p/24p would all require adding motion blur.
Note that we define general motion blur as applying to the motion of objects within a scene, and not just from camera motion. The latter also introduces motion blur, but is easier to correct for. This leads us to the following problem: if you capture at 24p, with a commonly used 180 degree shutter (1/24 * (180/360) = 1/48 second shutter speed), and try to upsample to 60p, then 1/48 second shutter speed will occur in output with 1/60 of a second between frames - or 360 x (1/48 / 1/60) = 450 degrees! This will cause the eye to perceive the scene as blurry, because the blur is not commensurate with the human vision queues arising from the higher frame rate and our ability to track motion. How can you reduce the blur? This is an unsolved problem for general motion. It is much easier to motion-blur than to motion-deblur! Even if an individual frame could be motion-deblurred, one could still get issues arising from inconsistencies that occur frame-to-frame (similar to deinterlacer flicker).
It is strongly recommended that the hierarchy of choices for cameras in terms of repurposing would be (best to worst):
60p, 60i (30ifr), 50p, 50i (25ifr), 48p,
and much worse:
30p, 25p, 24p
Note that this list does not change its order based on the output frame rates you wish to use, although 50 or 60Hz countries might reasonably prefer to shoot at rates based on their region in order to simplify or minimize the number of conversions.
Note: When adding simulated motion blur for FRC from 50p to 24p, some fine lines/details may appear less sharp than in the original 50p when viewed frame-by-frame. This same motion blurring would have occured on a real 24p camera.
No one in the business of high-end video capture should be using low frame rates just because of limitations
in distribution channels to rates such as 24p or 30p. This is especially true for sports or action sequences.
We hope that this article helps you make smart repurposing and future-proof choices when making production
decisions on the frame rates used, what cameras to use, and when preparing for a shoot.
Finally, offer our proprietary, IABM/NAB game-changer-award-winning Viarte-based media conversion services, include 100% vertical resolution deinterlacing, cinema-quality frame rate conversion (any-to-any) with the ability to add accurate simulated motion blur for down-frame-rate conversion, detail-retaining noise reduction, etc. For more information, visit Services.