PC to TV: frame rate v refresh rate

[hello_hello]

I have my PC hooked up to a Plasma TV using an analogue connection with the refresh rate set to 60Hz (using the "PC" input the TV supports a refresh rate of 60Hz, 60Hz or 60Hz).

I understand when watching 24fps video, 24 doesn't go evenly into 60 etc, but how is the difference in refresh/frame rates handled by the video card?
I'm basically wanting to know if it'd be applying 3:2 pulldown, or if it works in a way I'm unaware of. I ask because I'm not sure if I can see any judder, and kind of suspect I should be able to. Not that I'm complaining....

I've read a whole lot of refresh rate/frame rate info but generally it appears to refer to LCDs. I assume everything which applies to LCDs basically applies to plasmas too?

[setarip_old]

Hi! I ask because I'm not sure if I can see any judder, and kind of suspect I should be able to. Not that I'm complaining....I'd just call myself a happy camper and enjoy the quality visuals ;>}

[hello_hello]

I know I should, because if I keep thinking about it I'll probably start seeing imaginary judder anyway, but I am curious as to how the video card converses with the TV in respect to the refresh/frame rates. I guess somewhere along the way 24fps has to be combined with a 60Hz refresh rate....

Until I bought the Plasma I'd only been running the PC through the CRT monitors and their refresh rate is higher, and I guess being CRT, a frame/refresh rate match isn't so vital, but while I'm thinking about it.... how does the video card send 24fps to a CRT with a refresh rate of 85Hz? Does it repeat frames to match the refresh rate or can the frame rate and the refresh rate be independent when it comes to CRTs? I'm just trying to increase my understanding a little.....

[Blue_MiSfit]

Don't use VGA. Use HDMI, or (at least) component. In my experience, VGA inputs on HDTVs are resolution limited - i.e. even if you have a 1080p TV, you can't send a 1080p signal through VGA. Even if you can, you're probably going to get some blurring...

This isn't always the case, but I always recommend using a digital connection whenever possible.

Derek

[Ghitulescu]

Blue_misfist is right, VGA is intentionally blurred for some 15 years now, in order to fulfill the requirements of TCO95 then TCO98.

[hello_hello]

Don't use VGA. Use HDMI, or (at least) component. In my experience, VGA inputs on HDTVs are resolution limited - i.e. even if you have a 1080p TV, you can't send a 1080p signal through VGA. Even if you can, you're probably going to get some blurring...

This isn't always the case, but I always recommend using a digital connection whenever possible.

I've been meaning to try connecting via HDMI but still haven't got around to buying an adaptor (my video card only has DVI). However....

I'm pretty sure my TV accepts a 1080p signal via VGA. If I change the resolution to 720p on the video card, text and icons etc get a lot bigger, so I assume 1080p is really 1080p.
As far as the blurring goes... well if that's what's happening then in the case of my TV at least, it's a good thing.
I've compared a few different videos of different resolutions using both my PC and Sony Bluray player as the playback device, and the picture produced by the PC tends to look a little better. It seems to upscale a little better but even when playing 1080p video it looks more "natural". In fact I spent a bit of time adjusting picture settings trying to get the Bluray output to match the PC output but never quite got there. It's close, and the difference is really only something you'd notice with both videos running while switching between them but I prefer the PC's picture. I'll buy a DVI adaptor in the near future to see if the difference is the type of connector, or whether the PC's video card is just better than the Bluray player. If running the PC via HDMI improves the picture even more, it'll leave the Bluray player for dead. Unless of course, there's a blur which I think looks more natural....

Why would VGA be intentionally blurred?

[hello_hello]

On the subject of the judder I couldn't see... well I stupidly kept looking and now I can see it very occasionally, but really only if something is moving across the screen at an even speed, and even then it's got to be at just the right speed to notice any judder. A similar judder does occur using the CRT PC monitor too, but being a smaller screen I guess it's less noticeable. I made comparisons by remuxing video with a 30fps frame rate to see if it looked any smoother, but while sometimes it did, sometimes it just changed the judder effect.

It's hard to explain because I'm still trying I'm still trying to fully understand the way the video card outputs video to match the refresh rate, but one example....
I took a 720p episode of a TV series where the credits rolled past quickly (25fps) and were noticeably blurry/juddery. I guess it's more noticeable because the position of the credits on the screen changes quite a lot between frames. I then remuxed it at 30fps and fully expected the credits to run by quite smoothly (because of the 60Hz refersh rate), but they were still blurry and juddery, only the judder was more "even". Then I remuxed it at 60fps and the credits flowed by quite smoothly and without any blur. Not that there's anything I can do about it.... whatever the frame rate I'm just trying to understand how the video card/TV handle each display refresh during which the frame remains the same.... for want of a better way of describing it.

[madhatter300871]

Having the same problem here. My projector accepts 50hz/60hz refresh rates. the only way I can playback 23.976 video 100% smoothly is by speeding up to 25fps and outputing at 50Hz, and then its really really smooth.

I'm guessing that unless your video is played back at a true multiple of the refresh rate then there is no way at all you can get all the frames to display perfectly in sync.

So I am now also guessing that in the U.S. all film converted to NTSC must display with some judder, because US TV sets run at 60Hz but the NTSC video signal runs at 29.97fps, not an exact multiple (damn close though). Am I right or am I barking up the wrong tree here ?

If I am right then it is key to know for sure what the native refresh rate of the display is so you can best decide how to play content on it.

My TV, for example, says in the manual it accepts 24p, but I've not seen many blurays that have 24p content, its usually 23.976, so something has got to give here. Either the TV really accepts 23.976 (in this case 24p material would judder) or it does truly accept 24p (in which case 23.976 material will judder). What gives ?

I am slowly coming round to the idea that for me I'll be playing everything back at 25fps, I mean hey ... that's how all PAL DVDs are authored, so why the change with bluray ?

[Ghitulescu]

AFAIK the graphic card can cope with "integer" fps like 30 or 25 or 24 but not with 23.976 or 29.97.

[Asmodian]

AFAIK the graphic card can cope with "integer" fps like 30 or 25 or 24 but not with 23.976 or 29.97.

This isn't actually true; the performance at different refresh rates is different depending the specific card.

Check out this review:
Anandtech's Discrete HTPC GPU Shootout (http://www.anandtech.com/show/4380/discrete-htpc-gpus-shootout/5)

Edit: well it is true that integer refresh rates usually work but some cards can do the decimal refresh rates well too.

[manono]

So I am now also guessing that in the U.S. all film converted to NTSC must display with some judder, because US TV sets run at 60Hz but the NTSC video signal runs at 29.97fps, not an exact multiple
When people say 60Hz, they really mean 59.94Hz. And DVDs output 59.94 fields per second. If encoded as progressive 23.976fps with pulldown then, yes, there will be judder most noticeable during certain kinds of movement. The judder comes from that 3/2 playback pattern. As an NTSC person, I barely notice it and don't find it the least bit objectionable. PAL people viewing NTSC film material on DVD sometimes really notice it and sometimes really hate it.

If you have an 120Hz (really 119.88Hz) or a 240Hz (really 239.76Hz) TV set, then there's no judder. For film, the original interlaced output is 'intercepted', the fields reassembled into their component frames, and then the TV will play them 5 at a time (for 120Hz sets) or 10 at a time (for 240Hz sets). Even a progressive scan DVD player outputting to a progressive 60Hz display will also reassemble those fields into frames, but they'll be shown in that 32323232 pattern, and thus have the judder.

[hello_hello]

I see judder in places whether the video is progressive or not (once I stupidly went looking for it rather than remaining blissfully unaware). When I speed 24fps video up to 30fps I still see it. The difference being 24fps has the "pulldown" or "uneven" judder, whereas 30fps still has judder, it's just smoother or more even. At 60fps the motion is always perfectly smooth.
When I do see it, and it's really only when there's movement at just the right speed I guess, I don't find the "pulldown" judder any less annoying than the "even" judder. It'd be nice to be able to get rid of both of them. My PC's connected to a Plasma at 60Hz. A couple of times when I've seen a "juddery" section of video I've also played it using the Bluray player to see if it looks any different, but it doesn't. Reclock didn't help as I don't think dropped frames is an issue for me.

I'm seriously considering encoding everything at 60fps in the future, using a script to create "interpolated" frames. Admittedly it's slow, but the result is perfectly smooth natural looking video. http://www.spirton.com/convert-videos-to-60fps/
Another thought, which I haven't really experimented with a lot yet, is trying to use a script to convert the video to 60fps in real time, rather than encode it that frame rate. Then I can use it with my plethora of existing encodes. It works a treat on standard definition content, but not for HD stuff yet as I can't get it to use more than one CPU core. Early days.... anyone else tried converting to 60fps in real time and got it working. How fast a CPU would you need?

[manono]

The term 'judder' (aka 'telecine judder') refers specifically (usually) to the effect of pulldown, the 3 field (or frame) playback followed by 2 fields, by 3, by 2, etc. Therefore something that's progressive 30fps doesn't display 'judder' (as the term is usually, but not always, used), but ... what? ... jerkiness or something, from the framerate not being high enough. Thomas Edison, when trying to come up with the 'proper' framerate for the new movies back at the end of the 19th century, decided that 46fps would do the job. Of course, that wasn't ever adopted but there is talk these days of moving to a 48fps format. Isn't Peter Jackson doing that for The Hobbit?

http://www.firstshowing.net/2011/peter-jackson-talks-at-length-about-using-48fps-for-the-hobbit/

Does watching movies in a movie theater bother you in the same way and to the same degree?

Maybe you should check out one of the 120Hz or 240Hz sets and see if you prefer the interpolated frames they can produce. They'll entirely do away with the judder, but the experience is something completely new and different. Many don't like it; others do.

[hello_hello]

Yeah, I can tell the difference between judder and jerkiness, but if the motion across the screen is at just the right speed then it seems to be either one or the other, depending on the frame/refresh rate.

I'm not sure I've noticed "jerkiness" too much in a theatre, but then I'd be lucky to watch a movie that way more than once a year.

I only bought my Plasma recently but I've read mixed reviews regarding the TVs which produce interpolated frames, and they're more expensive, so I went for a more basic model. Thinking about it, I'm not even sure Plasmas come in the "interpolated frame" variety..... they probably do... but while I did look at a few different LCD TVs, I preferred the picture of a Plasma.

Given I generally watch video played on a PC which is hooked up to the TV, using it to fix the judder/jerkiness would solve my problem. I tried some experimental encodes using the script I linked to and it works a treat. The resulting 60fps encode looks perfectly smooth and natural, and if memory serves me correctly the file size didn't increase as much as I thought it would. I'll just have to play around a bit more to see if I can get it working in real time for HD video. I suspect the script will do a better job at interpolating frames than a TV could do, so it'd probably be the ideal solution. Obviously though it's pretty CPU intensive so at the moment I've only been able to get it to work in real time for standard definition video. I guess I should update AVIsynth to the MT version to see if that makes a difference. At the moment all the work is being done by a single core of the CPU, which doesn't provide enough processing power.

[Ghitulescu]

This isn't actually true; the performance at different refresh rates is different depending the specific card.

Check out this review:
Anandtech's Discrete HTPC GPU Shootout (http://www.anandtech.com/show/4380/discrete-htpc-gpus-shootout/5)

Edit: well it is true that integer refresh rates usually work but some cards can do the decimal refresh rates well too.

That is an excellent info source, but it still doesn't say too much about the real issue.
The issue is the hardware present on the graphic card. The reception part (TV, monitor etc.) is not usually an issue, if designed to cover these fps (if designed for 24fps it can do 23.976 almost always, as the PLL circuit for 24 can easily lock on 23.976, too).
The graphic card must have quartz clocks for each fps (yes, two for 24 and 23.976, two for 30 and 29.94 and so on), because the real difference is the product of three consecutive prime numbers (7, 11 and 13). These are extremely difficult to be obtained one from the other by simple mathematical operations from a single clock, or need tact signals in the order of tens of GHz in order to obtain eg 23.976 from 24, which poses other technical problems.
Only the cards with 3 quartz clocks (for 23.976, 24 and 25fps) are universally compatible (30 is obtainable from 24, so is 29.94 from 23.976). Cards having "user definable" fps would always be best at one fps and provide satisfactory results for another (but not best). On top of this, it comes the ability of the system (SO, drivers, player) to deliver the frames in the required cadence, which is another hurdle.