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Discussion Starter · #1 ·
Don't know if this is in right place, so feel free to have a mod move it.

I currently am in the process of setting up a setup where I have windows server 2012 running with Next PVR, Centon 6 Channel tuner, and Plex Media server. From there I want to use XBMC useing the Next PVR plugin as the live tv front end. I thought I would just load up a Raspberry Pi with XBMC, but then I saw that a Rasberry Pi only runs at 30fps. I was wondering if it makes a difference for sports because it is only running at 30fps (I heard that cable televisions max is 60fps) . Also how does HZ fit into the equation (would it just add more filler Frames).

Also I have a mix between 120hz tv and 240hz tv's.

One last question does anyone know if next pvr has a max fps/hz transfer rate.

Thanks
 

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I've never heard that the Pi only supports up to 30fps. This seems to suggest otherwise http://www.raspberrypi.org/forums/viewtopic.php?f=91&t=75589

In a typical situation historically the signal going to a television in North America is 59.94hz (often referred to as 60hz). The actual images making up this signal are either 24fps (23.976) for film or 30fps (29.97) for video. Interlaced "fields" add another level of complexity, so thats why historically your source device just figured out how to divide those various inputs into a standard 59.94/60hz signal.

Your tv refresh rate is completely seperate. Those various screen refresh rates are attempts to translate the source signal into smoother motion. You don't need to feed signal X to get the tv to refresh at signal Y. As I said historically televisions just accepted one signal rate (60), but now many can accept 24 as well. You won't be sending either of your tvs 120hz or 240hz.

In a perfect world live tv watching would be done at 60fps and movie watching would be done at 24fps. I don't know how well the Pi can be configured to spit out different signals like that. My television has a 600hz refresh rate, but only accepts a 60hz signal, so thats what I send it.
 

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60hz is 60 fields per second, and 2 fields makes one frame.

Example:
60hz is 30 frames /60 fields
120hz is 60 frames / 120 fields

No one really uses interlaced signals anymore. Well I guess they do with 1080i actually, perhaps I am wrong IDK.

All HD TVs can do 60 FPS or 60 Hz as that is in the spec. 60 Hz means the screen refreshes it's image 60 times a second, therefore a 60Hz TV is perfectly fine for achieving 60FPS. The 120 Hz that you see for LCD is an attempt by the makers to overcome an inherent weakness of LCD's that can result in afterimages and motion blur. By generating more pictures then the signal has (no signal has 60 fps, never mind 120) they hope to over come problems.

Film is only 24fps, but if you speed it up to 60fps it looks like video.
 

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No one really uses interlaced signals anymore. Well I guess they do with 1080i actually, perhaps I am wrong IDK.
Majority of cable is 1080i mpeg 2 with a few exceptions

By generating more pictures then the signal has (no signal has 60 fps, never mind 120) they hope to over come problems.
A lot of tvs that say 120Hz accept 60fps but not 24. With 60fps source, they can do several things. Some input a black frame, or inverted frame, or interpolated frame

Newer 240Hz and 480Hz sets will almost always accept 24. They will also input some black frames, as well as interpolated frames . . . if you have their motion-effect-whatever-they-call-it enabled
 

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60hz is 60 fields per second, and 2 fields makes one frame.

Example:
60hz is 30 frames /60 fields
120hz is 60 frames / 120 fields
I'm not sure about this. You always see 1080i30 and 720p60, which I assumed was due to bandwidth.

TCM HD is 1080i30. Check out the resolution and frame rate. I think Video Redo reports interlaced signals as PROG OR INT and progressive signals as PROG. Also notice the laughably low bitrate on the "HD" signal (but thats a topic for another thread) - its lower than DVD!.




FOX HD (at least my affiliate) broadcasts a 720p60 signal:

 

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A lot of tvs that say 120Hz accept 60fps but not 24. With 60fps source, they can do several things. Some input a black frame, or inverted frame, or interpolated frame

Newer 240Hz and 480Hz sets will almost always accept 24. They will also input some black frames, as well as interpolated frames . . . if you have their motion-effect-whatever-they-call-it enabled
I think most 120hz televisions at this point accept 24p signals. They can do one of a few different things, depending on the model and mode selected
-flash the same frame 5 times in a row (24x5=120)
-flash the same frame and mix in blank black ones (the number of blank ones determined by how "strong" the effect is)
-flash the real frame and interpolate artificially created ones
 

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I think for "P" sources like 480p/720p/1080p then just two fields = 1 frame so you just get all 480/720/1080 lines at the same time twice, where as with 1080i you get 540 of them, then the other 540. With oldschool 480i then it was 240 then the other 240.
Yea thats a good way of putting it. To add I found this on about.com that reitterates that

Progressive scan differs from interlaced scan in that the image is displayed on a screen by scanning each line (or row of pixels) in a sequential order rather than an alternate order, as is done with interlaced scan. In other words, in progressive scan, the image lines (or pixel rows) are scanned in numerical order (1,2,3) down the screen from top to bottom, instead of in an alternate order (lines or rows 1,3,5, etc... followed by lines or rows 2,4,6). By progressively scanning the image onto a screen every 60th of a second rather than "interlacing" alternate lines every 30th of a second, a smoother, more detailed, image can be produced on the screen that is perfectly suited for viewing fine details, such as text, and is also less susceptible to interlace flicker.
 

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Back when progressive was introduced I was selling video products at circuit city while I was still in college. I remember how I used to explain it was with my fingers and hands.

Basically spread out your fingers so that the fingers from one hand can pass through the spaces between the fingers on the other hand. Then bring one hand closer and farther away shifting back and forth. The fingers are like the lines, you get half then the other half, swapping back and forth. With progressive scan you'd get all the fingers at the same time, and twice as often to make up the difference in time.

Example probably does not translate well on the PC and text but in real life it's obvious the differences.
 

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I think for "P" sources like 480p/720p/1080p then just two fields = 1 frame so you just get all 480/720/1080 lines at the same time twice, where as with 1080i you get 540 of them, then the other 540. With oldschool 480i then it was 240 then the other 240.
It doesn't quite work like that. If your source is progressive, then there are no fields at all. All LCDs display progressive images and cannot display interlaced images at all. Only a CRT can display an interlaced picture. As such, all LCDs deinterlace 1080i signals to 1080p before displaying them, but because the source is 1080i, you only get effectively half as much vertical resolution (540 lines) when the scene is in motion. This is one of the reasons that 1080p from a Blu-ray looks better than 1080i from HDTV (the other main one being that Blu-ray effectively has 4x as much bandwidth to work with, which eliminates the compression artifacts that HDTV often has).

If you have a 120 Hz TV, then it works pretty much as pittsoccer33 described. You can divide 120 by 24, 30, and 60, so you can display any North American content without using duplicate frames, which makes the motion smooth. If your TV is only 60 Hz, then 60 is not divisible by 24, so you need to use duplicate frames during the extra screen refreshes, which makes the motion jerky.

Film is only 24fps, but if you speed it up to 60fps it looks like video.
Uhh... no. You wouldn't want to do that, because it would cut the runtime of your video by more than 50% and make everyone talk and move really fast. :D

Using duplicate frames to pad 24 fps to 30 fps and then showing each frame twice gets you up to 60 fps for the sake of a 60 Hz monitor, but those duplicate frames reduce the smoothness of the animation.
 

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60hz is 60 fields per second, and 2 fields makes one frame.

Example:
60hz is 30 frames /60 fields
120hz is 60 frames / 120 fields

No one really uses interlaced signals anymore. Well I guess they do with 1080i actually, perhaps I am wrong IDK.

All HD TVs can do 60 FPS or 60 Hz as that is in the spec. 60 Hz means the screen refreshes it's image 60 times a second, therefore a 60Hz TV is perfectly fine for achieving 60FPS. The 120 Hz that you see for LCD is an attempt by the makers to overcome an inherent weakness of LCD's that can result in afterimages and motion blur. By generating more pictures then the signal has (no signal has 60 fps, never mind 120) they hope to over come problems.

Film is only 24fps, but if you speed it up to 60fps it looks like video.


All ATSC sub-channels are 480i these days. ATSC HD broadcast is either 720p or 1080i. I have never seen a 1080p broadcast. Not sure what the native mode is for a standard DVD.
 

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Discussion Starter · #13 ·
Final

So at the end of the day the raspberry Pi will not decrease the quality I got from the cable source.

Also it will also transport it in the HZ the cable box provies it with either 60 or 24.

Also it will transport it in the FPS the cable box provides it with either 60 or 24.

Last question whats the difference between FPS and HZ when talking about source feeds.
 

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fps is used for "frame rate" of a video source (the number of frames, i.e. the complete pictures, included per second), while Hz is used for "refresh rate" (the number of the complete pictures refreshed per second) of a display device. 1080i cable TV is 30fps, but it is interlaced, so each frame is split to the odd field and the even field so 60 fields per second. Raspberry Pi should be able to send it as is (i.e. 60 fields per second or 1080i) to the display and the display device should be able to deinterlace it so that the video is converted to 60fps (for video) or 24fps (for movie) and displayed.

Or Raspberry Pi should be able to do basic deinterlacing task (i.e. bob) according to this discussion: http://www.raspberrypi.org/forums/viewtopic.php?t=18096, so that it outputs 60 frames per second instead of 60 fields per second and the display device does not have to deinterlace it.
 

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Discussion Starter · #15 ·
According the the forum post it should deinterlace natively, correct? Also is it better for the Rasberry Pi to deinterlace or the TV.


Thanks
 

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Yup, Raspberry Pi can do deinterlacing with a proper player, but it's only "bob" i.e. converts each field to a frame by merely doubling its vertical size. Usually TV can do a lot finer deinterlacing algorithms such as "motion adaptive" (Raspberry Pi is too weak to run such an algorithm).
 

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Discussion Starter · #20 ·
I tried a raspi. It was totally ineffective and unpleasant. Slow, and poor laggy performance. A $35 celeron chip runs circles around it, and can run of USB stick and XBMC just the same. Throw the raspi out and get a cheap PC oriented build. You'll be happier.
Would you be willing to share what other components you used for the Celeron build. Also do you have the celeron interlacing?
 
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