Judder created by 24 frames per second video (also called 24p) makes camera movement look stuttered, and is especially noticeable with panning shots. It is a result of a mismatch between the refresh rate of a TV panel and the frequency of 24 hz video, and can occur both over a 24p signal and when a 24p video is sent via a 60p or 60i signal.
Luckily, some TVs are able to adjust themselves and play 24p movies judder-free. A few can also remove judder from 24p video sent via 60p and 60i signals. As part of our testing process, we check whether every TV can do judder-free 24p, and also judder-free 24p via 60p/60i.
When it matters
24p judder only matters when you watch movies, so if you don’t watch movies, you have nothing to worry about.
Overall, 24p judder is not a major problem; most people will never even notice it. If you’re wondering whether it’s an issue for you, take a look at this video and compare the look of 24p with judder (left) to judder-free 24p (right). If you don’t notice the judder on the left, or it doesn’t bother you, there’s no need to worry about getting a TV that can do judder-free 24p. If you do notice it and it bothers you, make a point of getting a TV that can.
This evaluation verifies whether a TV has judder on 24p videos sent via a 24 hz signal. This will tell you whether a DVD or Blu-ray player, or a TV’s native streaming services, will have judder when playing movies. If you’re a big movie buff and use one of those mediums to watch movies, this test is somewhat important (more important if you’re bothered by 24p judder).
To conduct the test, we play a 24 fps video on the TV (download it here), sent from our PC over HDMI. The test video cycles a white square through 24 slots in one second. While it plays, we photograph the screen, using a 1 second exposure.
To pass this judder-free 24p test, a TV must be able to recognize that a 24 fps video is playing and adjust its refresh rate so that the video is played at 24 frames per second. If the color of the squares is a uniform grayish color, it means each of the 24 slots displayed the square for the same amount of time, and so the TV has passed the test (above, left). If certain squares are light, and others are dark, it means the TV failed to play each frame for an even amount of time, and therefore had judder (above, right).
Judder-free 24p via 60p
This test is to determine whether a TV has judder on 24p videos sent via a 60p signal. This will tell you whether movies played over a 60p signal (streaming devices, game consoles, etc) will have judder. If you hate judder and watch movies over one of those devices, you should get a TV that passes this test.
This test uses the same test process used in the judder-free 24p test, but with the 24p video sent over a 60hz progressive (60p) signal. To pass, a TV must be able to recognize that a 24 fps video is playing over a 60p signal, and adjust its refresh rate so that the video is played at 24 frames per second.
Once again, if the color of the squares in the resulting photo is not even, the TV has judder.
Judder-free 24p via 60i
We also test whether a TV will have judder when playing a 24p video sent via a 60i signal. This will tell you whether movies played over a 60i signal (mainly cable & satellite boxes) will have judder. If you watch lots of movies through your set-top box and don’t like the look of judder on 24p video, this is an important test for you.
This test uses the same test process used in the judder-free 24p test, but with the 24p video sent over a 60hz interlaced (60i) signal. To pass, a TV must be able to recognize that a 24 fps video is playing over a 60i signal, and adjust its refresh rate so that the video is played at 24 frames per second.
As with the other 24p judder tests, if the color of the squares in the resulting photo is not even, the TV has judder.
The cause of judder on 24p video
TVs commonly have one of two refresh rates: 60 hz and 120 hz. 30 hz and 60 hz videos divide into those refresh rates evenly, which makes it easy for the TV panel to get the video to meet the panel refresh rate. For example, a 30 hz TV show would have each frame displayed four times on a 120 hz panel.
Likewise, most 120 hz panels can display 24 hz video without issue, because 24 goes into 120 five times. But some 60 hz TVs have difficulty. Because 24 does not divide into 60 evenly, doubling the frame rate still leaves 12 frames missing from meeting the TV’s refresh rate. To get to 60 fps, 60 hz TVs use a feature called ‘telecine,’ or 3:2 pulldown. This makes the video’s frames alternate displaying two and three times – hence 3:2 – which makes up the missing frames. The image below illustrates this.
The video lingering on some frames longer than others adds a jerkiness, or judder, to the movement when there is a camera pan. There’s jerkiness to other movement too, but it’s less obvious than what you see with a pan. To get around this, it’s necessary to get a TV with a film mode that reverses the telecine, as that will eliminate judder.
The cause of judder on 24p via 60p/60i video
If you’re watching a movie off of cable, or from a PC, you may see judder even if your TV can play movies from 24 hz sources judder-free.
The problem: the signal being sent from the cable box or PC is likely 60 hz (either 60p or 60i), so even though the movie is 24 hz, your TV is registering a 60 hz signal. This means telecine (3:2 pulldown) is altering the frame rate of the 24 fps video so that it is 60 fps, which could create judder.
How to get the best results
Here are the settings to enable to get judder-free 24p on compatible TVs.
- Samsung: Automatic most of the time, but inconsistent – sometimes 24 fps video will have judder via 60p and 60i. For 480i and 1080i video, go to Menu > Picture > Picture Options and set ‘Film Mode’ to ‘On.’
- On some TVs, setting 'Auto Motion Plus' to 'Custom' with both sliders to 0 will fix it without adding any soap opera effect.
- Sony: Go to Menu > Picture and Display > Picture Adjustments. Set ‘MotionFlow’ to ‘TrueCinema,’ and set ‘Cinemotion’ to ‘High.’
- Vizio: Go to Menu > Picture > More Picture and set ‘Film Mode’ to ‘Auto.’
- LG: Go to Menu > Picture > Picture Mode Settings and set ‘Real Cinema’ to ‘On.’
- Motion interpolation settings can also remove judder from 24p video. Keep in mind that interpolation can sometimes introduce occasional frame skipping to the video, and also adds the soap opera effect. We talk more about motion interpolation here.
- When testing for 24p judder, we never use interpolation during these tests. It increases the frame rate, which defeats the point of testing for judder-free playback of 24 fps video.
24p judder makes camera movement in movies look stuttered. It’s not a huge deal for most, but could be a pain for people who are sensitive to this kind of issue. We test to see whether a TV has judder on 24p movies sent via a 24p, 60p, and 60i signal, which covers just about any device or service you might use to watch movies.
To avoid 24p judder, get a TV that supports judder-free playback over whatever signal type you normally use to watch movies, and then enable any of the necessary settings we outlined above.
Questions & Answers
I am interested in buying the Samsung JU6500, which according to your reviews doesn't support 24p playback.
Is there anyway to make the problem less noticeable or is there any possibility of a firmware update to alleviate the playback judder?
If you want no judder when you are watching a movie, you can change your graphics card's output to 24 fps. You will need to do it manually and remove it each time, though.
Judder isn't very noticeable, so it's not something to worry about much. Odds are good that it isn't going to bother you.
As for a future solution, it's certainly possible that one could be released with a future OneConnect box, or even potentially with a firmware update. You could also get around the issue by setting your laptop to output a 24 hz signal, which won't have judder.
Even though the set is 60hz, it seems like you are saying that the panel can change the refresh rate for different purposes, so it can achieve true 24p even though it is not 120 or 240hz. Is this correct? I just want to make sure that the set doesn't have to apply something artificial (such as some version of motion interpolation) to achieve 24p at 60hz.
A related question: I know streaming devices such as Apple TV output at 60 hz. Do they also adjust their refresh rate when playing back 24p content, or does it have to use 3:2 pulldown? If Apple TV can't output 24p, is there a setting on the TV (aside from motion interpolation) that corrects this and achieves 24p from these devices? Finally, does this Vizio set automatically play back 24p content from native smart TV apps (like Netflix) at 24p, or would I have to make sure film mode is set to on or auto? Thank you!
Some devices can output proper 24 fps - Xbox and PlayStation are two examples - but Apple TV does not. That said, some TVs, including the M, can detect this and do the reverse 3:2 pulldown.
You'll need to set Film mode to 'Auto' to get the streaming apps to do judder-free 24p.
Thank you for your feedback. We do our judder tests with 1080p signals. Using 4k signals is a test we can consider adding in the future. A 120Hz display helps because it means a 24p source over a 24Hz signal can be played by repeating 5 frames. For the judder tests of 24p over 60p or 60i, it depends more on the processing of the display (reverse 3:2 pulldown) and not on the refresh rate. The 120Hz is useful for people who like the soap opera effect, and motion interpolation. This is a personal preference.
We have just tested our KS8000 with a 4k signal and found that movies over 24p play smoothly, and movies over 60p play smoothly when 'Auto Motion Plus' is set to 'Custom' and both sliders to 0. The TV does not support a 4k @ 60i signal.
We watch broadcast (antenna) TV, DVD movies, and use an old ReplayTV (480p, I assume) which we love because it automatically strips out the commercials. We also will want to be able to stream video off the web. Which sub-$1,000 (street price) TV would you recommend that can upscale from this old technology, has 24p support, minimal motion blur, good sound, and of course a great picture?
There is so much marketing hype and "double-speak" out there. I love your reviews and how you explain the features and underlying technology. Thank you.
Unless you can find a different reviewer that also tested this, the only way would be to test the TV for yourself. The simplest way would be to connect your PC to the TV, and then play a movie with a panning shot. If you notice a slight jittery look to the pan, you're noticing judder.
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