Judder Problem with 23fps clips in 1080p - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 4 Old 01-03-2011, 08:09 PM - Thread Starter
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When I am connecting my 120Hz LCD TV to my Laptop(via VGA port) I can see a lot of Judder during scenes with panning for a MP4 video clips(1920 x 1080) with frame rates 23fps.

Now the same video clip if I play directly in my TV (Yes it has a USB port to play directly from flash drives) then I don't see any judder. I checked my TV setting and it has "120Hz Smoothing effect" turned on. And yes, if I turn it off I see judder effect even when playing directly in the TV.

After the above observations I tried to turn on "120Hz Smoothing effect" on my TV while connecting it back to Laptop's VGA port. But it won't allow me to do so as the option itself is disabled when connecting to my PC through VGA port.

My laptop has ATI Mobility Radeon HD 3400 Series. And the processor is Intel Core 2 Duo P9500@ 2.53Ghz. RAM = 4GB
My TV is Samsung LN40C630

1. Now I am trying to build a HTPC from scratch and I am worried do we really have a good Graphics Card(GPU) which can work at 120Hz?
2. OR we really don't need 120Hz GPU to reduce judder?
3. What are the other ways to reduce judder?
4. Anything to do with HDMI? Will a card with HDMI port reduce the judder?
5. Any recommendation for Graphic cards for full 1080p movie viewing @ 120Hz

Sorry if my questions are stupid ... I am kind of new to these things.

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post #2 of 4 Old 01-04-2011, 12:13 PM
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First, while your TV can display a 120hz signal, it cannot accept a 120hz signal, so whether or not your video card can output at 120hz is irrelevant.

Second, your smoothing effect probably works when you hook up via HDMI port. So you need a video card with HDMI or DVI and a DVI --> HDMI adapter. Monoprice.com has them for next to nothing.
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post #3 of 4 Old 01-06-2011, 12:50 AM
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Your laptop would probably be outputting the 23fps (actually closer to 24fps) video as 1080p60: this would result in judder because 23/24 doesn't go into 60 evenly.

It is highly unlikely your TV would be able to convert the 1080p60 input back to 23/24fps (and then internally multiply that evenly to 120Hz) to reduce the judder.

However, if you were to output 1080i60 from your laptop (interlaced, not progressive), your TV might have the ability to convert it back to 1080p24 internally.

When you play the 23/24fps video directly on the TV, I expect it retains the original 23/24fps and so is able to smoothly multiply that to 120Hz.

Your problem is the conversion that the laptop is doing, because 60Hz is a VGA standard.

As someone else mentioned, if you can output HDMI via a DVI->HDMI adapter from the laptop to the TV and set the laptop refresh to 24Hz, you will probably notice less judder.

If you can't do this, I would suggest trying 1080i60 output from the laptop and see if the TV has a feature to convert that back to 23/24fps for display.
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post #4 of 4 Old 01-06-2011, 03:07 PM
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some things to note.

24P is not the most common encoding rate. 23.97 known as 23 is. most Nvidia and some ATI cards do not do 23.97 they only do 24. What compounds this is that they will tell the user they are outputting 23.97, but if you use a program to snoop they are really outputting 24.

Next: depending on your TV the same problem will be there. Just becasuse it says it does something... in this case 23 does not mean it will. Also if you are using the overdrive (i.e 120) with 23.97 content every 40th frame or so will repeat. This could be the judder you are seeing. If you turn overdrive off and play the movie at the given refresh rate you can determine if the issue is the TV or something in the computer.

Anandtech or Tomshardware has a good article on this or just do a wed search. I will see if I can find the article and post the link.


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