Guide for connecting HTPC to flatscreen (1 Viewer)

[knutinh]

it is connected via VGA--> VGA and is running at 1360*768@60Hz

How good is that VGA connection for transferring 50fps "PAL" material?

i also tested it (very quickly) with a hdmi-->hdmi connection and it was also very cool.i have not tested any DVI-->hdmi tricks, but i suppose its right what people say, the only thing is: i cant imagine how the picture coul be any better then it already is now with VGA (-;

Are you saying that you setup your PC to 1360x768, connected PC to tv using DVI/HDMI and the tv displayed the entire picture, no scaling, cropping etc?

In that case I would have to revise my view of Sammie.

-k

 

[smnnekho]

it is connected via VGA--> VGA and is running at 1360*768@60Hz

How good is that VGA connection for transferring 50fps "PAL" material?

well. i never really thought about that? does it really matter via a PC? looks fine to me. I'll test @ 50hz when i'm @ home though.

i also tested it (very quickly) with a hdmi-->hdmi connection and it was also very cool.i have not tested any DVI-->hdmi tricks, but i suppose its right what people say, the only thing is: i cant imagine how the picture coul be any better then it already is now with VGA (-;

Are you saying that you setup your PC to 1360x768, connected PC to tv using DVI/HDMI and the tv displayed the entire picture, no scaling, cropping etc?

In that case I would have to revise my view of Sammie.

-k[/QUOTE]

no, thats not what i said.

vga-->vga fine
DVI --> hdmi NOT TESTED
hdmi-->hdmi: fine

(-;

 

[knutinh]

it is connected via VGA--> VGA and is running at 1360*768@60Hz

How good is that VGA connection for transferring 50fps "PAL" material?

well. i never really thought about that? does it really matter via a PC? looks fine to me. I'll test @ 50hz when i'm @ home though.

It matters if you like movement. For still-images they look the same ;-)

i also tested it (very quickly) with a hdmi-->hdmi connection and it was also very cool.i have not tested any DVI-->hdmi tricks, but i suppose its right what people say, the only thing is: i cant imagine how the picture coul be any better then it already is now with VGA (-;

Are you saying that you setup your PC to 1360x768, connected PC to tv using DVI/HDMI and the tv displayed the entire picture, no scaling, cropping etc?

In that case I would have to revise my view of Sammie.

-k

no, thats not what i said.

vga-->vga fine
DVI --> hdmi NOT TESTED
hdmi-->hdmi: fine

(-;

Well, as HDMI is a superset of DVI I tend not to separate those two.

So you have got a HDMI equipped graphics card, connected it to a Samsung lcd-tv using a HDMI cable, setup your desktop to 136x*768, and got a nice sharp picture with no scaling, cropping or overscan?


For more info:
http://reclock.free.fr/
"What is it ?
The purpose of ReClock is to definitely get rid of jerky playback of AVI and MPEG material on a PC (or a HTPC driving a TV, a flat panel, or a video-projector). It's a DirectShow filter which is loaded in place of the default directsound audio renderer.
It provides a new reference clock that is locked to the video card hardware clock, in order to ensure that frames are played at the exact speed of what is expected by the video card vertical sync.
It also provides a frame rate adaptator for media files that do not match a multiple of the video card refresh rate (ex: playback of 23,976fps IVTC NTSC on a PAL TV).
The combination of the two will give you the true experience of smooth playback with your PC.
Finally it is an audio renderer with hardware or software rate adaptation in real-time, multi-channel audio, audio timestretching (pal speedup compensation) and dynamic range compression capabilities.
For a full description of ReClock, please read carefully the README file in the distribution. There is also a little FAQ at the bottom of the page that answers common questions. You can also visit the forums here to meet other users.
...

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What is ReClock?
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Said simply the purpose of ReClock is to definitely get rid (I hope) of jerky playback of AVI and MPEG material on a PC (or a PC connected to a TV).

ReClock is born from my own frustration. I have a fast PC, a good video card, and when I play a DVD or DIVX on my brand new Home Cinema, I get dropped frames here and there for no reason, or a completely jerky and un-watch able movie. This is very annoying.

The following sections will give you a complete and I hope clear explanation of what cause jerky playback, and how ReClock will try to solve these problems.

The last section will give you the instructions on how to install and use ReClock.

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The not so great history of frame rates
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In basic terms, a video can be thought of as being made up of numerous snapshots, called frames. The frame rate is the number of frames displayed each second

As you know there exist 3 common broadcasting formats: cinema, TV, and computers

Cinema is the oldest. It is the format of the movies you see in your favourite theater. Cinema movies play at 24 frames per second ( fps). It’s very simple: every 1/24th of a second, your see a new frame. This is also called “progressive scan”.
A television, however, does not deal with video in terms of frames. Instead, it displays video using half-frames, called fields. Each frame contains exactly two fields. One field is made up of the odd horizontal lines in a frame. This is called the odd field or the top field since it contains the top line of the image. The other field is made up of the even horizontal lines in a frame. This is called the even field or bottom field. This way to broadcast video is called “interlaced scan”
Now there are three common TV standards: PAL, SECAM and NTSC. All of them use “interlaced scan”.
Let’s start with PAL, which is the European TV standard. It is also used for DVD and DIVX material. PAL material is played at 25 fps (or 50 fields per second). You see the first problem here: how can we play a 24 fps movie on a 50 fields per second PAL TV? Well first of all, we can present each movie frame two consecutive times to make the movie play at 48 fields per second. But playing the movie like this would give jerky playback every second because one movie picture would be missing. So the movie is just played 50/48 times faster to match 50 fields per second. So a cinema movie that has duration of 60mn plays on PAL in 57mn36 seconds. That’s why movies you watch on your PAL TV are always a bit shorter in time.

SECAM is the French brother of PAL and works exactly the same way. It is still used in France because it gives better colours when broadcasted by radio waves (less sensitive to noise).

And now here is NTSC, the American brother of PAL. NTSC is also used for DVD and DIVX material, and plays somewhere near 29.97 fps (to be exact it is 4.5 MHz/286/525). You see a bigger problem here. How can we play cinema movies on NTSC. Accelerate them? Sure no, because you would notice that the film plays much too fast (a 60mn movie would play in 48mn3s). So NTSC engineers came with a solution called “telecine” or “3:2 pulldown” which is quite complicated. To convert a film that runs at 24 fps to run at 29.97 fps, it is first necessary to slow down the video by 0.1% to 23.976 fps. Then approximately 6 frames are added to the video each second, bringing the frame rate to 29.97 fps. This is done by adding one extra frame to each group of 4 film frames. Although they could simply duplicate 1 out of every 4 frames to produce the extra frame, this method is not used. This is because the duplication of one frame would cause that frame to be displayed for twice as long as the other 3 frames, which leads to jerkier motion. Fortunately, film producers can make use of the field-based nature of video to more gradually introduce the extra frame. Instead of adding a whole new frame at once, 2 fields are introduced separately to each group of 4 film frames. Since 2 fields make up a frame, this method is equivalent to adding 1 new frame. However, since the 2 duplicated fields are not added at the same time, this reduces the jerkiness of the video.

Let’s finish with computers. Computers are quite simple, they just do work like cinema and use “progressive scan”. But they use many more frame rates: 60 Hz, 75 Hz, 85 Hz, 100 Hz when watching your monitor, 50 Hz when connected to a PAL TV, and 60 Hz when connected to a NTSC TV. To obtain a smooth playback on a PC you just have to make sure that your video card uses a refresh rate that is an exact multiple of the movie you play. You can already see that PAL can be played fine at 50 Hz, 75 Hz or 100 Hz, but NTSC cannot be played without begin jerky because all we have is 60 fps which is not a multiple of 29.97 fps.


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The nightmare of badly born DIVX
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DIVX for the most are created from DVD material, and DVD material generally comes from movie material.

DIVX created from PAL material are generally fine, because they were created from 24 fps material simply accelerated to 25 fps or from direct 25 fps material. PAL is a good guy.

And now you have telecine for NTSC. Since telecine can only be displayed correctly on “interlaced scan” hardware, it must be removed for PC playback. This operation is called “inverse telecine”. Doing this on a film will revert the frame rate of the movie to 23.976 fps. Funny, but … jerky on every PC you will use to play the movie.

Some people that create DIVX from NTSC don’t even know that inverse telecine must be done. So those DIVX stays at 29.97 fps and will have artefacts when watched on your PC because interlacing artefacts do not compress well at all.

And to add another thing to the story, some DIVX has sound and movie sync problems that are solved by … modifying the frame rate a little bit so the movie duration matches the sound track duration. This is a quick and dirty way to do it. Imagine a 25 fps DIVX that is modified to play at 25.001 fps; well every 1000 frames (that’s only 40 seconds) the playback will become jerky.


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The bigger nightmare of PC hardware
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When you connect your PAL DVD player to your TV, things are really simple. Your player read the movie from the disc at 25 fps, and sends the signal to the TV at 25 fps.
Now imagine that your player is a little too fast and send the movie to the TV at 25.01 fps. What will happen? Jerkiness? No … In fact your TV is smart, and will stay synchronised with your player as long at the player plays near 25 fps. To be more precise no player in the world plays the movie exactly at 25 fps because clocks are never accurate. So every player play the movie “near” 25 fps, but this is no problem for your TV since it is locked to the video signal it receive.

Now when you play a DIVX on your PC and watch it on your PC what happens? First of all, if the refresh rate of your monitor is not a multiple of the frame rate of your DIVX, jerkiness will happen for sure. Do you remember that DIVX can be 24 fps, 25 fps, 23.976 fps, 29.97 fps, or even 25.001 fps? This is the first and main cause of jerky playback.

The other source of jerkiness is much more subtle and harder to understand. Suppose you play a 25 fps movie on you PC. Well your PC isn’t smarter that any DVD player, it will play it “near” 25 fps because it uses its internal clock, which is inaccurate. But it should not be a problem because DVD players also do that? Bad luck, it is a very big problem, because your video card does not synchronise its speed with the speed of the movie like a TV would do with a DVD player. In a PC the clocks used in the video card (to show the video) and in the PC (to play the video) are completely distinct, thus there always is deviation between them, and then jerkiness is inevitable.


"

-k

 

[Spragleknas]

Thank you su much for that! Cleared up things a bit. I really enjoy reading your tech-posts - and somtimes I even understand it!

Please keep sharing your wisdom - seriously!


Q1: Do you then recommend that "all" users should use ReClock? (Stupid Q, perhaps)
Q2: "t's a DirectShow filter which is loaded in place of the default directsound audio renderer." Changing the directsound renderer in MP often causes stuttering. Should I then be worried when trying ReClock? If all goes to hell; a simple uninstall will bring everything back to normal?

 

[CHli]

Q1 : Yes but it will mainly benefit non SPDIF users, and ReClock is not compatible with every sound card driver I think. But you can try, see Q2.
Q2 : No problem with trying, Yes uninstalling will resolve any problem.

 

[knutinh]

To be really honest, I have uninstalled Reclock on my system. In theory, it should be the cure to all problems.

However:
*It does not do any good for live (tv) sources
*It does limited good in case you are decoding DD/dts streams in your surround-receiver

Also, it seems to me that it is difficult to get a setup that just works - without user-interference. My GF does not respond nicely to pop-up-boxes stating anything involving "24p-IVTC"

Many HD-sources seems to be "dirty" with mixed telecine, interlacing and weird framerates. This evidently is difficult for Nvidia purevideo and Reclock (and any other combination that I have tried) to get right. Typically, you get occasional stutters, occasional frames with combing (bad deinterlace/IVTC), etc etc.

Sadly, my lcd-tv wont do 24/48/72 Hz and wont do 1:1 pixel at any usable frame-rate, meaning that I am still forced to accept 2 passes of scaling and/or nasty framerateconversion from e.g. ~24fps to 60fps. The world is far from ideal

I am still waiting (and willing to shell out) for a combined audio/video card with HDMI out and hardware synchronised clocks so that audio and video will always be in sync without doing any software trics.

-k