Pick The Right Video Frame Rate

Posted on by Larry

One of my readers wrote in recently asking how to decide what video frame rate to shoot. So, in the interests of contributing to the discussion, here are my thoughts.

BASIC THEORY

Here’s my take: You pick the video frame rate that yields the image “sharpness” that you want.

By this, I mean that the slower the frame rate, the greater the motion blur on all moving objects. The greater the motion blur, the harder it is to see the edges of things.

A TRIP BACK IN TIME

Projected film first appeared between 1877 and 1880. And, in the earliest days of recording, film was shot on cameras that were hand-cranked. In fact, the mark of a good camera operator was not their framing, but how steadily they could turn the crank to keep the recording speed of the film constant.

Film was new enough in those days that anything that moved would draw a crowd. But, while hand-cranking film cameras was fine for comedy, because the speed changes enhanced the comedic effect; hand-cranking cameras played hob with dramatic scenes.


Gradually, by 1920, producers and studios replaced hand-cranked cameras with motor-driven cameras. However, there was no standard for frame rate. While it was generally agreed that a frame rate of 16-18 frames per second was necessary to give the illusion of movement, industry practice varied frame rates between 12 and 26 frames per second. And there was no guarantee that the projectionist would display the film at the frame rate at which it was shot.

Producers would often select slow speed frame rates to save on film costs, while theaters would often project films at faster frame rates so they could fit more movies into an evening (i.e. sell more tickets). Since there was no audio synced to picture, no one really knew what speed anything needed to be shot or played at.

This situation changed instantly with the advent of The Jazz Singer, arguably the first “talking” picture. Suddenly, the sound track was on the same strip of film as the picture. Any changes in film speed would be immediately noticed in the audio.

The industry huddled to answer the question: “What is the slowest possible frame rate we can use (to reduce film stock costs) that yields the highest quality audio?” And the answer became 24 frames per second.

Not necessarily because it looks “filmic,” but because it provided the best balance between limiting film stock expenses and providing acceptable audio.

NOTE: A sidebar to the frame rate issue is that in order to minimize frame flicker from projecting 24 fps film, which is a strobing effect seen by the audience when frame rates get too slow, the actual projected image needs to be quite dark. As total projected illumination increases, so does the perception of frame flicker. This is one reason movie theaters are so dark.

FAST FORWARD TO TODAY

There is a lot of debate on the new “high-frame rate” method of shooting film at 48 frames per second. This first rose to the level of public debate with the release of “The Hobbit.”

Long advocated by Roger Ebert, and others, the benefit to faster frame rates is that images contain much less motion blur, which results in much crisper images. These higher frame rate images can also be projected using much brighter lamps, without displaying frame flicker.

UPDATE

My background is video, not film. Some characteristics of film, like shutter angle and shutter speed, I have not completely figured out. So, I’m happy to add the following comments supplied by Philip Hodgetts.

[Larry, let me add]: the higher frame rate the higher the shutter speed by necessity, which is why the image is sharper. (In film this would be called “shutter angle.”) Some film and video has a super sharp (too much imnsho) image where the shutter speed is way faster than the “normal” shutter speed for that frame rate. Each frame rate has a default shutter speed, roughly [half] the frame duration. At 24 fps the frame duration is 1/24th of a second, so the default shutter speed is 1/48th second. (This gives the default looks that Larry talks about in the article.) At 24 fps and 1/200th or even higher shutter speed the image will be super sharp, but the motion will be much less smoother. To me it’s a very disturbing look, but it’s a creative decision if you want to over-ride that.)

Another interesting addition is that film is rarely projected at 24 fps. In perfect conditions flicker fades from perception at about 18fps, which is the speed (on average) of most silent films.  24 fps is the minimal acceptable speed for sound-on-film. Even in a very dark theater, with that big screen, 24 fps projection is going to flicker, which is why each frame is projected twice (or even 3 times) for an effective “flicker” rate of 48 or 72 flickers-per-second, [making it] much less perceptible.

Thanks, Philip. Always pleased to learn new stuff.

HOW TO CHOOSE

For me, the choice comes down to motion and effects. Higher frame rates will yield cleaner motion with the ability to create better effects when chroma-keying or rotoscoping because edges are sharper and contain much less motion blur. (It is far easier to add motion blur in post production, than to remove it.)

Everything I shoot is at 60 frames per second.

For projects going directly to the web, the frame rate doesn’t make any difference, YouTube and the rest can easily handle whatever frame rate you shoot.

When going to cable or broadcast, 60 frames per second in North America, and 50 frames per second in the rest of the world, are standard.

For theatrical release, your choices are more constrained. Film output still needs to be 24 fps. However, for digital projection, you have, essentially, the same frame rate options as you do for the web. With the shift from film to digital, the old constraints of 24 fps (and its cousin 23.976 fps) become less and less important.

As with all projects, always verify what your deliverables need to be before you start shooting. It is FAR easier to shoot at the correct frame rate than it is to convert to it after all shooting is complete.


9 Responses to Pick The Right Video Frame Rate

  1. Julik says:

    Hey Larry, a note here. With all due respect, the ‘motion sharpness’ issue is tertiary at the least! I’ve seen quite a few videos withwrong framerate which were unfixable, so for me there are two primary considerations always:
    – Yuor feamerate should be acceptable with the light you are using. Most non-LED light including available light and practicals flickers at your AC frequency. So if you shoot in tge US, shoot at 30 to fut into tge cadence of the US light – unless you shoot outdoors or you can afford lights that have flicker-free ballast AND you dont forget to switch it! This is no joke. If a ceoss-phase flicker bleeds into your footage the effect will be much more disastrous than a not-exactly-pleasing shutter.
    – Consider your deliverables. Most of todays screens on computers sync to 60 hz, even in Europe. So when you edit on a vomputer screen or output deliverables for the Web there will be spme frame-skipping or interpolation involved if you are not at 30 fps. Even for 24fps material. Broadcasters demand different framerates still – in Europe you will be bound to the 25fps. If you shoot at a different feamerate you will have to speed up or slow down your audio for thus – and you will have the same issue of not being able to use practicals or available light if yoy shoot 24 instead of 25/50i.

    And only AFTER you took care of the two things above you should look for the best shutter setups that look pleasing.

  2. Norman Whitelaw says:

    Thank you for a very interesting piece of information.

  3. ron heydon says:

    Hi Hope you can help
    I live in New Zealand ( pal ) and have purchased a pal camera from ebay
    aghvx200p
    In the recording set up it is all 60i ( ntsc ) and not 50i ( pal )
    Any idea why or how to change to 50i
    ANY HELP APPRECIATED.
    rON hEYDON

    • Larry says:

      Ron:

      First, the camera may have been misrepresented to you as supporting PAL when it does not.

      Second, if possible, you are better off shooting 25p, rather than 50i, just to get rid of interlacing – your images will look better and it is easy to convert 25p to 50i when you need it.

      Third, as I haven’t shot with that camera, you’ll need to download or access the user manual to see how or if you can convert it to PAL.

      Larry

  4. Josh says:

    Hey Larry,

    Thanks for the great article.

    Just to clarify- you talk about camera set up and shooting frame rate.

    Can you tell me if all the editing should be done in exactly the same frame rate?

    I shoot at 50p on Gh4 (and up to 120p on the gopro) . I am setting up projects in FCP at 25fps, but it all looks a bit skippy . I am assuming that these inconsistencies in frame rates are causing the issues. Any suggestions?

    Cheers Josh

    • Larry says:

      Josh:

      In general, yes. You want to edit at the frame rate you shot. However, switching from 50p to 25p should be fairly seamless. Make sure you are setting your project to progressive, not interlaced.

      Larry

  5. julia anderson says:

    I’m trying to frame rate you can’t hide so i can animate it can you anser it

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