The truth about 23.976 frames per second

L

Leo123

n00b
Joined
Jul 27, 2009
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57
Hi,

I am thinking of building a small Sandy Bridge-based HTPC but the one thing that is putting me off is the issue over the onboard graphics not being able to handle 23.976fps.

There is so much on the web about this being a problem but not much on people with first-hand experience.

1. In what exact circumstances will not being able to play slightly below 24fps actually result in a problem? (i.e. a judder)
2. Is this a problem that is actually noticeable?

Thanks v much.

A
 
Leo123 said:
I am thinking of building a small Sandy Bridge-based HTPC but the one thing that is putting me off is the issue over the onboard graphics not being able to handle 23.976fps.

There is so much on the web about this being a problem but not much on people with first-hand experience.

1. In what exact circumstances will not being able to play slightly below 24fps actually result in a problem? (i.e. a judder)
2. Is this a problem that is actually noticeable?
Click to expand...
You're confusing graphics output with video output. This concern is a non-issue.
 
If you're looking for better video output, you could look into an llano apu instead.
 
Foronine said:
If you're looking for better video output, you could look into an llano apu instead.
Click to expand...
That's still graphics output. The OP is looking at specs that have to do with actual video output, ie: video broadcasting -- which is a non-issue for HTPC using graphics output.
 
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I am not sure I really understand the difference between video and graphics output.

In what circumstances would the 24fps of HD2000 graphics cause a judder to video?
 
Leo123 said:
I am not sure I really understand the difference between video and graphics output.

In what circumstances would the 24fps of HD2000 graphics cause a judder to video?
Click to expand...
In the computer desktop world, "graphics card" and "video card" are used interchangeably. In the broadcast world, they are two distinct entities. Graphics cards deal with pixels and refresh rate; video cards deal with fps, resolution, refresh rate, and refresh pattern (bottom field first, top field first, progressive).

Some of the terms may still seem ambiguous or interchangeable, but there is a distinct difference. Some examples of video card vendors would be from Aja, BlueFish, or Black Magic Design. Personally, I use the Black Magic Intensity Pro quite often. These cards ingest and output raw video streams, and often have native broadcast-style connections like SDI. Also, the cards are not detected on a computer as a desktop card. You will not be able to use them as a second monitor to see your desktop.

However, all of the above gets away from the point that the primary issue you're describing is likely a codec issue. And the next step to testing is playing the same file in VLC Player, as they use their own internal codecs instead of whatever else is installed on the machine. If both your first player and VLC shows issues, then chances are it is an encoding issue and you should try re-encoding in a more standard way.

As for the 23.97, 23.976, 24, 29.97, 30, etc for fps, I have all of the above on my development box in a variety of video containers (MP4, MOV, MPEG2, WMV, etc.), and across many framerates, stream types, encoding sources, etc. I don't have issues playing through the Intensity Pro card as raw video stream, and Windows Media Player and VLC Player all work fine as well through my graphics card.

If there truly is something wrong with Intel's IB graphics driver, then you're likely stuck waiting until Intel releases a fix as a driver update and/or BIOs update -- which is not really a different scenario than if ATI or NVidia had the possible issue. But we're still a little ways away from IB release: Q2 2012.
 
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It's not really noticeable. If it bothers you, a really cheap AMD or nVidia GPU from at least the ATi/AMD HD2000 generation, or the nVidia 9000 generation would do fine (some of the 8000 generation cards had a really inadequate video decode block).
 
PTNL said:
In the computer desktop world, "graphics card" and "video card" are used interchangeably. In the broadcast world, they are two distinct entities. Graphics cards deal with pixels and refresh rate; video cards deal with fps, resolution, refresh rate, and refresh pattern (bottom field first, top field first, progressive).

Some of the terms may still seem ambiguous or interchangeable, but there is a distinct difference. Some examples of video card vendors would be from Aja, BlueFish, or Black Magic Design. Personally, I use the Black Magic Intensity Pro quite often. These cards ingest and output raw video streams, and often have native broadcast-style connections like SDI. Also, the cards are not detected on a computer as a desktop card. You will not be able to use them as a second monitor to see your desktop.

However, all of the above gets away from the point that the primary issue you're describing is likely a codec issue. And the next step to testing is playing the same file in VLC Player, as they use their own internal codecs instead of whatever else is installed on the machine. If both your first player and VLC shows issues, then chances are it is an encoding issue and you should try re-encoding in a more standard way.

As for the 23.97, 23.976, 24, 29.97, 30, etc for fps, I have all of the above on my development box in a variety of video containers (MP4, MOV, MPEG2, WMV, etc.), and across many framerates, stream types, encoding sources, etc. I don't have issues playing through the Intensity Pro card as raw video stream, and Windows Media Player and VLC Player all work fine as well through my graphics card.

If there truly is something wrong with Intel's IB graphics driver, then you're likely stuck waiting until Intel releases a fix as a driver update and/or BIOs update -- which is not really a different scenario than if ATI or NVidia had the possible issue. But we're still a little ways away from IB release: Q2 2012.
Click to expand...
You're overthinking this. Its a matter of the internal clock generator in the clarksdale GPU being incapable of producing an ouput at 23.976 FPS (or Hz). The output signal is only capable of producing 24.000 FPS, which results in a framerate mismatch on "24p" content, which is actually 23.976 FPS. This results in an extra frame at a set interval, which introduces the judder the OP is talking about. This defect is also present in the HD2000/3000 Sandy Bridge generation iGPU because this part of the chip was copied directly from Clarksdale without modification. It is not a driver issue and it cannot be fixed. it is unavoidable for 24p (aka most Blu Ray) playback.

How noticeable it is... well thats completely a matter of personal preference. If you don't notice it you'll never care, but other people get driven crazy by it. If you want more information, the HTPC forums are probably the best place, since the problem is pretty much limited only to 24p movie content. I'm also not 100% sure what kind of workarounds there are and whether different playback software and refresh rates change anything, since I've always used a discrete card or, in my current case a Zacate APU, which do not have the design flaw.
 
Activate: AMD said:
You're overthinking this. Its a matter of the internal clock generator in the clarksdale GPU being incapable of producing an ouput at 23.976 FPS (or Hz). The output signal is only capable of producing 24.000 FPS, which results in a framerate mismatch on "24p" content, which is actually 23.976 FPS. This results in an extra frame at a set interval, which introduces the judder the OP is talking about. This defect is also present in the HD2000/3000 Sandy Bridge generation iGPU because this part of the chip was copied directly from Clarksdale without modification. It is not a driver issue and it cannot be fixed.
Click to expand...
Ah, I wasn't aware of this carry-over issue. Thanks for the clarification.
 
Thanks very much for everyone's help with this. So this is only a problem with Blu Rays?
I actually have a i3-2120 in my desktop computer, so I guess the best thing to do is actually watch a Blu Ray on it and see if I notice the difference.

You are absolutely right about this thread having been started in the HPTC section. Is there any way I might be able to move this thread over there rather than reposting?

Thanks again.
 
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