Why doesn't my TV and HTPC output 24p correctly? (1 Viewer)

[Nazgulled]

Hi there,

For a couple of months now that I have this TV:
http://uk.lge.com/products/model/detail/lcdtv_37lg5000.jhtml

And if you scroll down a bit on the specifications you'll see the following:
1080P Source Input: HDMI 60p/50p/30p/24p Component 60p/50p

So, I guess my TV is supposed to support 1080p24p, right?

On to the HTPC part... My HTPC is brand new, it has only about a week but I've been looking for custom parts over the past couple of months to pick the best ones for my needs and I ended up picking an Asus M3N78-EM motherboard with the GeForce 8300 integrated graphics chipset.

And I saw the following on this review:

24 fps Playback: Perfect on NVIDIA

Most movies are recorded at 24 frames per second, however most displays and graphics cards refresh the screen 60 times per second (60Hz). Enter the home theater space and you'll find a number of displays that can properly output a 24 fps signal, but with an HTPC you'll need a video card that can properly output a 24Hz signal. Support for 24 fps playback isn't necessary, but you'll find that without it wide panning shots won't be smooth as the camera moves from one point to the next. The reason is that it's impossible to evenly divide 24 frames into 60, so some frames end up being displayed more than others (the infamous 3:2 pulldown).

On one end of the spectrum we have Intel's G45 which absolutely does not support proper 24p playback. The G45 still does not have official support for it in the drivers and although 24 fps playback is possible in the hardware, we seriously doubt the software group will implement it (that's a dare).

The AMD 780G/790GX results were very choppy at times; even when they seemed smooth we experienced audio sync problems.

The only platform that can properly handle 24 fps output is NVIDIA's GeForce 8200/8300. It just works.

I have all the drivers updated, including the graphics ones and I can see that in the NVIDIA Panel control under "Change the signal or HD format" I can select the signal format to be "1080p24 HDTV". After applying that, I can see on the Windows display properties that the TV frequency is set to 23Hz (dunno if this is correct or if it's a bug) but I can also select 24Hz. I tested my issue (which I'm about to explain below) with both 23Hz and 24Hz at 1920x1080 through HDMI.

My problem is that I don't think that I'm truly seeing a 24p signal. As far as I read about it and what everyone tells me is that the movie should be very smooth, specially on "panning" scenes, but I don't see that. I'm testing this on some MKV files, all of them seem to have a framerate of 23,976. Is that the problem? Does it need to have exactly 24 frames a second? All I know is that if I set my graphics card to output at 50Hz, the image is smoother than at 23Hz/24Hz.

Any ideas on what my problem might be?

 

[frankwaan]

Hi,

The fact that on 50Hz 24 (or 23.976) content looks better because 2x24 = 48 which lies close to 50.

However, when I watch a blu-ray rip (23.976 fps), it's still not very smooth. Even when using reclock, it isn't just as silky as SD content (PAL) is.
Lately I watch a stand alone blu-ray player (on a LCD display) ... smooth as silk.

Anyone knows how to improve smoothness with 23.976 (and 24) fps content?

 

[Nazgulled]

The fact that on 50Hz 24 (or 23.976) content looks better because 2x24 = 48 which lies close to 50.

Yeah, I thought of that too and it makes sense but I think there's something weird going on, let me try to explain this the best I can...

When I play a movie at 50Hz I don't notice any stutter of any kind but in slow (but not too slow) panning scenes you can easily see that there's room for improvement, that the panning is not as smooth as possible.

That panning improves a bit when I put the TV at 24Hz, it's much smoother like that. I know this contradicts my first post but this where the problem starts and I've written my first post before testing this on scene which allows me to notice the problem better.

The problem is that, although 24Hz seems smoother on panning scenes and the like, for some strange reason, the image freezes by a very small instant every single second. I don't think this should happening, 23,976 fps is much closer to 24Hz than 25Hz (half of the real refresh rate, 50Hz). As I see it, this "freezing" should happen at 50Hz and not that 24Hz.

Any reason for this?

 

[frankwaan]

That's strange, indeed. For some reason i cannot get the 23.976 (or 24) fps content smooth....

Do you also play MKV's ?

 

[Nazgulled]

I'm actually talking just about MKVs, I can't afford a Blu-Ray drive for the time being...

 

[frankwaan]

Yeah, I currently don't have a blu-ray drive neither. So for the time being I play MKV's also. Like I said, I can't get them completely smooth (like TV / other SD content). I read an article somewhere that states the encoding isn't always done right. I'll get more into that later and post back.

Greets, Frank

 

[Jeditrav]

I'm wondering if it's possibly an issue with the TV. When I play blu-ray off my PS3 at 24fps, and my TV is set to 24hz, I also get a slight 'hiccup' every second. I'm wondering if maybe some of these tv's, when set to 24hz, just take the 24fps and 'repeat' one of the frames every second (to 'fit' the 24 frames into the tv's native 25fps/50hz), rather than just playing 'true' 24fps/24hz. If I have the PS3 set to PAL output, 25fps/50hz, I get smooth blu-ray playback. Interestingly, I too have an LG tv. I hope I'm wrong and I hope we're not being screwed by our TV manufacturer - if anyone can prove otherwise it'd be much appreciated!

 

[mhunter]

Just to let you know, I get 24p out of the same motherboard (Asus M3N78-EM) with my Toshiba 37" TV.

It plays back really well (very, very smooth), however I then get issues with audio syncing. What I have done is gone for 60hz output from the HTPC, and because the TV is capable of 120hz (2x60hz), the frames divide nicely (120/24 = 5). So this plays back just as well without audio syncing issues.

With the LG TV you have there, it looks like your missing the feature (i.e. True motion), however you have "Cinema 3:2 / 2:2 Pull down Mode" which should do the 24fps to 50/60fps conversion for you. make sure this is ON (but try if off aswell). Nvidia also have this in the drivers but it probably only works on some things and I could never see a difference with it on or off (it's called "inverse telecine" in the drivers).

Being in Australia, I've found 50hz works best for TV and 60hz works best for 24fps content.

In the nvidia drivers try select "1080p" and select 24hz seperately via "change resolution", rather than picking 1080p24.

BTW I have tried this with FFDSHOW H.264 and MPC-HC H.264 decoders and both work well (which codec are you using? Perhaps try another?)

Cheers

Matt.

 

[frankwaan]

Just to let you know, I get 24p out of the same motherboard (Asus M3N78-EM) with my Toshiba 37" TV.

It plays back really well (very, very smooth), however I then get issues with audio syncing. What I have done is gone for 60hz output from the HTPC, and because the TV is capable of 120hz (2x60hz), the frames divide nicely (120/24 = 5). So this plays back just as well without audio syncing issues.

With the LG TV you have there, it looks like your missing the feature (i.e. True motion), however you have "Cinema 3:2 / 2:2 Pull down Mode" which should do the 24fps to 50/60fps conversion for you. make sure this is ON (but try if off aswell). Nvidia also have this in the drivers but it probably only works on some things and I could never see a difference with it on or off (it's called "inverse telecine" in the drivers).

Being in Australia, I've found 50hz works best for TV and 60hz works best for 24fps content.

In the nvidia drivers try select "1080p" and select 24hz seperately via "change resolution", rather than picking 1080p24.

BTW I have tried this with FFDSHOW H.264 and MPC-HC H.264 decoders and both work well (which codec are you using? Perhaps try another?)

Cheers

Matt.

hi Matt,

Do you also play MKV files? And you're not using Reclock at all? You just put your TV in the refresh rate which suits best?

Thanks, Frank

 

[Nazgulled]

With the LG TV you have there, it looks like your missing the feature (i.e. True motion), however you have "Cinema 3:2 / 2:2 Pull down Mode" which should do the 24fps to 50/60fps conversion for you. make sure this is ON (but try if off aswell).

I've been through the TV menus several times and I never saw something like that... I'll take a second look next weekend when I get home...

In the nvidia drivers try select "1080p" and select 24hz seperately via "change resolution", rather than picking 1080p24.

I normally set the resolution manually through Windows display properties, but it's all the same as long as I set it to 24Hz cause I realized that 1080p24 actually changes to 23Hz (for some strange reason).

BTW I have tried this with FFDSHOW H.264 and MPC-HC H.264 decoders and both work well (which codec are you using? Perhaps try another?)

I'm using CoreAVC for H.264/x264 playback. I know the nVidia chip handles DXVA just fine but that still has a couple of issues with subtitles and I prefer to use CoreAVC and have subtitles the way I want.

Maybe the problem is really on the TV and the fact that allows 24Hz is not enough? Where can I read more about that "true motion" thing? I can't find anything about it...