Tag Archives: 25p

More on frame rate choices for todays video productions.

This is another of those frequent questions at workshops and online.
What frame rate is the best one to use?
First – there is no one “best” frame rate. It really depends on how you want your video to look. Do you want the slightly juddery motion of a feature film or do you want silky smooth motion?
You also need to think about and understand how your video will be viewed. Is it going to be watched on a modern TV set or will it be watched on a computer? Will it only be watched in one country or region or will it be viewed globally?
Here are some things to consider:
TV in Europe is normally 50Hz, either 25p or 50i.
TV in the North America is 60Hz, either 30p or 60i (both actually 29.97fps).
The majority of computer screens run at 60Hz.
Interlaced footage looks bad on most LCD screens.
Low frame rates like 24p and 25p often exhibit judder.
Most newer, mid price and above TV’s use motion estimation techniques to eliminate judder in low frame rate footage.
If you upload 23.98fps footage to YouTube and it is then viewed on a computer it will most likely be shown at 24p as you can’t show 0.98 of a frame on a 60Hz computer screen.
Lets look first at 25p, 50i and 50p.
If you live in Europe or another 50Hz/Pal area these are going to be frame rates you will be familiar with. But are they the only frame rates you should use? If you are doing a broadcast TV production then there is a high chance that you will need to use one of these standards (please consult whoever you are shooting for). But if your audience is going to watch your content online on a computer screen, tablet or mobile phone these are not good frame rates to use.

Most computer screens run at 60Hz and very often this rate can’t be changed. 25p shown on most computer screens requires 15 frames to be shown twice and 10 frames to be shown 3 times to create a total of 60 frames every second. This creates an uneven cadence and it’s not something you can control as the actual structure of the cadence depends on the video subsystem of the computer the end user is using.

The odd 25p cadence is most noticeable on smooth pans and tilts where the pan speed will appear to jump slightly as the cadence flips between the 10 frame x3 and 15 frame x 2 segments. This often makes what would otherwise be smooth motion appear to stutter unevenly. 24p material doesn’t exhibit this same uneven stutter (see the 24p section). 50p material will exhibit a similar stutter as again the number of padding frames needed is uneven, although the motion should be a bit more fluid.
So really 25p and 50p are best reserved for material that will only ever be seen on televisions that are running at 50Hz. They are not the best choices for online distribution or viewing on computers etc.
24p, 30p or 60p (23.98p, 29.97p)
If you are doing a broadcast TV show in an NTSC/60Hz area then you will most likely need to use the slightly odd frame rates of 23.98fps or 29.97fps. These are legacy frame rates specifically for broadcast TV. The odd frame rates came about to avoid problems with the color signal interfering with the luma (brightness) signal in the early days of analog color TV.
If you show 23.98fps or 29.97fps footage on a computer it will normally be shown at the equivalent of 24p or 30p  to fit with the 60Hz refresh rate of the computer screen. In most cases no one will ever notice any difference.
24p Cadence.
23.98p and 24p when shown on a 60Hz screen are shown by using 2:3 cadence where the first frame is shown twice, the next 3 times, then 2, then 3 and so on. This is very similar to the way any other movie or feature film is shown on TV and it doesn’t look too bad.
30p or 29.97p footage will look smoother than 24p as all you need to do is show each frame twice to get to 60Hz there is no odd cadence and the slightly higher frame rate will exhibit a little less judder. 60p will be very smooth and is a really good choice for sports or other fast action. But, higher frame rates do require higher data rates to maintain the same image quality. This means larger files and possibly slower downloads and must be considered. 30p is a reasonable middle ground choice for a lot of productions, not as juddery as 24p but not as smooth as 60p.
24p or 23.98p for “The Film Look”.
Generally if you want to mimic the look of a feature film then you might choose to use 23.98p or 24p as films are normally shot at 24fps. If your video is only going to be viewed online then 24p is a good choice. If your footage might get shown on TV the 23.98p may be the better choice as 23.98fps works well on 29.97fps TV’s in 60Hz/NTSC areas.
BUT THERE IS A NEW CATCH!!!
A lot of modern, new TV’s feature motion compensation processes designed to eliminate judder. You might see things in the TV’s literature such as “100 Hz smooth motion” or similar.  If this function is enabled in the TV it will take any low frame rate footage such as 24p or 25p and use software to create new frames to increase the frame rate and smooth out any motion judder.
So if you want the motion judder typical of a 24fps movie and you create at 24fps video, you may find that the viewer never sees this juddery, film like motion as the TV will do it’s best to smooth it out! Meanwhile someone watching the same clip on a computer will see the judder. So the motion in the same clip will look quite different depending on how it’s viewed.
Most TV’s that have this feature will disable it it when the footage is 60p as 60p footage should look smooth anyway. So a trick you might want to consider is to shoot at 24p or 30p and then for the export file create a 60p file as this will typically cause the TV to turn off the motion estimation.
In summary, if you are doing a broadcast TV project you should use the frame rate specified by the broadcaster. But for projects that will be distributed via the internet I recommend the use of 23.98p or 24p for film style projects and 30p for most other projects. However if you want very smooth motion you should consider using 60p.
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Motion “Judder” on the FS100 and other video cameras at low frame rates.

There have been a number of threads in various forums about the way the images from the new Sony FS100 appear to judder or stutter when shooting at 25P or 24P. Most of the complaints appear to be coming from PAL areas where shooting 25P is common. This is not an issue unique to the FS100, in fact motion judder is often more noticeable with video cameras than film cameras even though the frame rates and shutter speeds may be exactly the same. Why is this?

One of the key issues here and I believe a very strong clue to what is going on is that most complain that the issue is most pronounced in areas of high contrast.

Our visual system picks up edges and other areas of high contrast to detect motion, in areas of high contrast any non-smoothness of the images motion will be more noticeable. The higher the resolution/contrast or more precisely the higher the MTF of the camera system the more we will notice judder and stutter.  Just take fast motion in an Imax film as an example, it stutters like crazy.

The FS100 and similar high contrast/resolution cameras will appear to stutter at low frame rates more than a low contrast/low resolution camera. Edges in film are almost never instant changes from black to white, there is almost always some smoothing or dithering caused by the grain structure of film. So when you consider the FS100’s near complete lack of noise, which through it’s random nature will help mask judder and stutter and you have a worst case scenario. A camera with sharp edges and no noise.

Another strong contributing factor is the use of detail correction that adds a very definite, hard, non-motion blurred black or white edge around any areas of medium to high contrast, so unlike the very slightly dithered edges we would see in film we have instant light to dark or dark to light transitions occurring over a single pixel. In the case of a pan that hard edge is going to step uniformly from one position to the next, it won’t have any motion blur and it will increase edge contrast compounding the images judder as our visual system will notice these hard edges jumping from one place to the next.

The PMW-F3 although it uses the same sensor is less prone to this effect as it has a more sophisticated DSP and uses less detail correction and more aperture correction for image sharpening. Aperture correction blurs with motion as it is a type of high frequency boost and as you pan the camera the motion blur of the image reduces high frequencies so the amount of correction also drops thus helping smooth edges as you pan.

You also need to consider the results of watching 25fps video on a computer monitor typically running at 60hz. You will get judder as 25 does not go into 60 evenly, this helps explain why this “issue” is getting more airtime in Europe than in the US where 24P with pull up to 30P is common and of course 30P will display on a 60Hz monitor with no additional problems.

So in the case of the FS100 (or other cameras exhibiting this effect),  I would suggest turning off the detail correction circuits or at the very least reducing the detail level if you are shooting high contrast images or anything with a lot of motion. It would also be interesting to compare similar pans at different speeds with some gain added to see if that helps.

I don’t think this is, as claimed by some, to be camera fault, more likely a result of a very clean, detail corrected image. Even an EX1 or EX3 will do similar things if your detail settings are too high. It’s not unique to the FS100, just one of those things that can happen when you have sharp pictures. When I watched the Sony F65 4k demo film “The Arrival” I noticed a similar increase in motion judder compared to film, again I put this down to high edge sharpness catching my eye and making me notice the cameras motion more acutely. Ohh that F65 stuff looked stunning!