Video frame rate is a big selling point for cameras offering video capability, but what do these numbers mean, what do you need and what’s the best speed to use for slow-motion footage?
Well-specified hybrid cameras will come with a wide range of video-focused features included these days but, for those who have yet to seriously venture into filmmaking or who are new to this side of the business, it can be confusing at times working out exactly what’s on offer and whether it’s going to suit the needs of your operation.
Yet again this could be the time to sit down with an impartial expert who’s more concerned with supplying you with the gear you actually need rather than making a quick and lucrative sale. It’s the way they do things at CVP, and it means that your needs will be fully explored and then they will recommend something that can genuinely deliver what you need.
Take video frame rates, for example. If you’ve only ever shot stills these will be outside anything you’ve encountered before, but once they’ve been explained they will make perfect sense and, from there, you’ll be able to work out what you’re going to need and what you might possibly be able to live without. The push at the moment is towards ever higher frame rates, with smooth slow motion being the ultimate goal, but with this on board you’ll obviously be paying for features over and above the standard, and you’ll need to be sure that this is something you really need.
It’s all about stepping back, considering the clients you have and the services you’re looking to offer, and building in a certain amount of future proofing. To do this you’ll need to get your head around what frame rates are all about and the effect that they will have on the footage you’re outputting.
The Basics
Frame rates, otherwise known as frames per second (fps or simply p), tell you the speed you’re shooting at. If you’ve set your camera to 24fps, for example, it’s straightforward to understand that each second of footage you shoot will consist of 24 separate images, each one representing 1/24th second. The reason that 24fps, the standard for cinema, was selected has its roots in history and dates back to a time when the cost of film was high and studios were looking to save on costs by choosing the slowest speed they could get away with.
Humans can typically recognise ten to 12 passing frames as identifiable individual images but, beyond that point, the brain begins to discern the images as motion. Settling on a standard of 24fps back when motion was becoming established gave a smooth enough result but was also economical to produce, so that’s ultimately what was decided.
However, you will benefit from having options and the more that are on board, the more you’ll be able to experiment with different video frame rates as you become more proficient. And naturally, if you shoot at a higher frame rate – typically twice your standard shooting speed – and then play the footage back at your normal rate then the footage will be slowed down and you’ll have a slow motion sequence, something that can offer a wide range of creative possibilities. Select an even higher frame rate, which is something the more sophisticated hybrid cameras are starting to offer as standard, and you’ll have an even slower sequence to work with.
“Having the flexibility to capture a range of frame rates will only make your camera more versatile,” confirms CVP expert Jake Ratcliffe, “and it will open up some interesting and creative new options for you. Looking at the basics first, however, there are two different types of frame rates you need to understand. The first of these is your playback or base frame rate, and this will depend on what you are acquiring and who you are delivering to.
“There are three standards under the umbrella of playback rates that you need to be aware of: 23.98 or 24fps, which is the standard for cinema, 25fps which is the standard for television in the UK or any other country that uses the 50HZ power standard and 30fps, which is the standard in the US or any other country that uses the 60HZ power standard.”
Shooting Slow Motion
Beyond the standards for real time motion capture, you can then move to the second option, which is to increase the frame rate to create slow motion footage and, technically, this will be anything that’s above 30fps.
“Most mirrorless cameras will start their slow motion options at 50 and 60fps,” says Jake, “which you can then slow down in post-production or in-camera to the base frame rate of your choice for delivery. This is hugely important, because slow motion is such a crucial part of modern filmmaking.
“When it comes to slowing things down there are a few things to be mindful of. The first will be your shutter speed. The rule of thumb for natural motion blur when shooting video is normally to set a speed that’s double your frame rate, so if you’re shooting 25fps your shutter speed would be 1/50sec. This also applies as you up the rate so, if you’re shooting at 100fps, your shutter speed would be 1/200sec. However, you can change this depending on how you want your footage to look but, if you’re aiming for a natural-looking result, doubling your frame rate is the way to go.
“The majority of modern mirrorless cameras will allow you to shoot most base frame rates that you might need, and also to film at 50 or 60fps, which will be half speed depending on your region. Your delivery frame rate will depend on your client, while whether you decide to shoot slow motion footage is very much up to the creative requirements of the individual.”
Used sparingly, slow motion sequences can add hugely to a production, especially one where movement is a key feature. Filming an athlete exerting themselves to the full as they race down a track, for example, will reveal every ripple of the muscles, each contortion of the face, and will emphasise the effort that’s being made. Similarly, slowing down the movement of something like a bird of prey in flight will help to accentuate the drama of its powerful wings in action, slowly beating as it moves through the air. There are also other benefits of slowing down the footage, such as making camera shake less noticeable, which can make hand held sequences easier to manage.
These days there are some amazingly well-specified hybrid cameras available, such as the Panasonic S1H and the latest Sony a7S III, that can drive the frame rate up still further, to 120fps and above, which slows the action down even more. This is a hitherto unheard of feature to be found in a relatively affordable hybrid model, and it just goes to show how far technology has advanced in recent years. However, impressive as it is, will the average filmmaker find that faster is better?
“The difference between 60fps and 120fps depends on which camera you are shooting with,” says Jake. “However, for the most part you could experience a reduction of quality when shooting at higher frame rates, perhaps because of more compression or reduced colour subsampling and bit depth. Resolution can also be commonly affected since you could find that you can only reach the higher speeds by shooting with the sensor cropped, which will obviously also reduce the field of view you’re achieving.
“And it could be that, if you’re a commercial operator, you might not need the very highest speeds in any case. With cameras like the a7S III shooting up to 240fps it’s possible to really capture all of the nuances in motion. However, the image fidelity of the 240fps HD that’s produced won’t ultimately be as good as the 4K 120p that the camera is also capable of, which looks absolutely fantastic!”
One of the most important things to remember is that you need to use the effect sparingly and justify why it’s being employed. It’s easy to be so smitten with slo-mo when you’re first starting out that it can become addictive and prone to overuse. Also keep sequences short and sweet, otherwise you could risk losing the attention of your audience.
Choosing Your Rate
Just because the accepted standard film rate for a particular audience is a certain number, it doesn’t necessarily mean that you need to stick rigidly to this for every piece of footage you shoot. It is possible to push the boundaries and to go with non-conventional speeds and, provided you know what you’re doing, the results can look very impressive. Famously, for example, director Peter Jackson shot The Hobbit trilogy of blockbuster films at 48fps throughout for the look it offered him, an exercise that ultimately received mixed feedback from critics.
“When it comes to the different base frame rates, they will ultimately change how your video looks,” explains Jake. “The higher the base frame rate, for example, the smoother your video will appear. This could be good for things such as sports or anything where you want to capture the details in movement, but could look rather odd for certain other applications, so it really comes down to what you are capturing and who you are delivering it to.
“One particular thing to be wary about is lighting when shooting at different video frame rates, since you could end up with flickering if you’re moving away from the frame rates these fixtures were designed to operate at. Because of this, it’s really important to test out your fixtures before taking on a commercial job to make sure that they perform as they need to.”
Finally, these days it’s very common to be shooting video content for online use, and here the parameters are different again. If you’re producing content exclusively for the likes of YouTube or Facebook you don’t need to adhere to the conventional TV or cinematic standards. In fact, there’s so much flexibility built into these platforms that there’s no recommended best frame rate to use. YouTube suggests that ‘content should be encoded and uploaded using the same frame rate that was used during recording. Common frame rates include 24, 25, 30, 48, 50 and 60 frames per second, while other frame rates are also acceptable.’
So, what you decide to go for could be down to the type of content you’re creating. If you’re filming travel vlogs, for example, and want to capture a cinematic look, you might choose to work with 24 or 25fps. If, however, you’re working with a subject that’s full of fast-paced action, it could be that a higher frame rate might work better for you, allowing you to lessen the natural blur in the footage that would result from the choice of slower frame rates.
It’s clear there is a lot to think about as you’re starting out in this area but, then again, it will all start to make perfect sense once you start working with video. Just make sure that you give yourself the best opportunity by investing in a camera that comes with plenty of options.
Next Month:
Codecs can be bewildering but they’re not as complicated as they might at first appear. We’ll be looking at the regular options and the ones you should be looking to use in your own business.
Jake Ratcliffe
One of CVP’s resident team of technical experts, and a self-confessed camera nerd who gets way too excited over kit, Jake’s background mirrors that of so many creatives these days. After graduating with a degree in photography he took up a freelance career and found that many of his clients were asking for video services so, rather than turn the work away, he started to teach himself the filmmaking basics. Having been based at CVP for four years now, Jake epitomises the ‘equipment agnostic’ approach of the company and devotes his time to advising customers who might be looking for impartial feedback on which products to invest in as they look to make the same journey into motion.
If you’d love to learn more about the ins and outs of the camera industry, you might be interested in our upcoming events at CVP.