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23.976 Hz refresh rate - impossible?

Discussion in 'Rivatuner Statistics Server (RTSS) Forum' started by puntloos, Apr 22, 2009.

  1. puntloos

    puntloos Member

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    Hi,

    I think the subject says it all.. but some explanation if needed..

    Movies are pretty much always 23.976 fps. Nvidia standard drivers - even with the custom resolution settings - will not do 23.976. (best I can get is 23.980)

    Suggestions?
     
  2. Pill Monster

    Pill Monster Banned

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    Oh noes not this gain......:bang:


    Nevermind just an inhouse joke....









    No you can't and No you don't want to.

    Refresh rate is NOT the same as FPS...........


    Have a nice day.:)
     
  3. puntloos

    puntloos Member

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    Ah! Smugness :)

    Care to let me in on the joke?
    :( why not? No way to (for example) remove 24fps mode and only keep 23.976? Tried to do a custom mode - failed. No way to tweak modelines? I tried powerstrip and a few other things.. no luck.
    Oh I think I do
    Maybe I explained it a little shortly, fine, if you take it literally then t is something else. But I suppose I should elaborate then.

    The movie is shot in such a way that if you play it back at 23.976 frames per second, it will play for exactly the right time. Why is this important? Because the audio, for example DTS or AC3 is encoded to run exactly the same length. And, the decoding of AC3/DTS is done by my receiver, not by the computer, so the audio will not be slowed up or down by frame rate differences.

    (no, you don't want to decode by computer, because the output is HDMI, which only takes PCM/AC3/etc and you don't want to decode, then re-encode to send it over HDMI.. encoding AC3 on the fly is bad, quality wise, but it is also pretty unstable currently)

    For this reason, I need to play back the video at exactly 23.976 fps. Now if the refresh rate of the TV, set by the video card, is not exactly 23.976 fps as well, funny things happen. If the computer is 'aware' of this discrepancy, it will compensate by doing stuff like 3:2 pulldown, or interpolating, or if I'm unlucky, it will introduce judder. If no hardware is aware of this difference, which happens when we're at 24 and 23.976 respectively, then audio/video will slowly desync.

    Yes. Perhaps try again with some more detail?
     
  4. Pill Monster

    Pill Monster Banned

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    Ok , refresh rate of your TV has no bearing whatsoever on how many fps your movie will play at.
    The only time this becomes an issue is when the fps are higher than the refresh rate of the tv/monitor, hence screen tearing. 3:2 pulldown is used when converting a video from one format to another, because different formats use different frame rates. It's nothing to do with your refresh rate.. As far as I know there isn't much you can do about interpolation, it's a consequence of converting video formats. That's what the 3:2 pulldown is used for, as well as stopping A/V desynchronization..
     

  5. puntloos

    puntloos Member

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    This is true, or at least mostly.
    - The video card sets the refresh rate of the TV
    - TV refresh is usually pre-defined by the user, not defined by the movie or the player (that would be nice..)
    Yes. That's what I said :)
    Exactly the point. I do not want to convert, or interpolate or reencode. My TV is capable of playing back the movie at the same framerate as the source movie. In theory everything can be sent unaltered to my TV + receiver.
    Yes. And this is what we do not want. I don't want a changed, then recoded/converted/pulldowned video, which then gets corrected.

    The source is 'perfect' and as far as I know all the hardware I have can play this source without altering. The only thing needed is having the video card output video at exactly 23.976.
     
  6. Pill Monster

    Pill Monster Banned

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    I think I see where this is going - have you got some downloaded HD movies you'd like to watch on your TV?
     
  7. ElementalDragon

    ElementalDragon Ancient Guru

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    puntloos: eer.... no.... it's not the VIDEO CARD that sets the refresh rate of the TV. Yes, you can change the refresh rate using the video card.... but typically only to refresh rates that the TV can support, unless you force a refresh rate, which could damage the TV.

    This also isn't the day and age where software/games were controlled solely by computer speed (Kind of like how if you run Scorched Earth on a remotely recent computer, you'll have a hell of a time playing it). I have never had a situation where audio was "slowed down or sped up" because of the refresh rate of a monitor.

    To elaborate a bit on the "FPS =/= refresh rate" thing a bit.... movies will play at the framerate they were designed to play at (typically around 24 fps). Your TV has a refresh rate typically anywhere between 60-160hz (depending whether it's LCD or CRT). Your refresh rate has absolutely zero impact on how many frames per second a video is played at, nor does it have an impact on synchronization with sound or distortion of sound.
     
  8. Pill Monster

    Pill Monster Banned

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    You can't. And unless you watch the movie on a 24 fps projector at a movie theatre I don't think you'll be able to avoid any interpolation either.....
     
  9. roguesn1per

    roguesn1per Ancient Guru

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    HD movies are 25/50 or 60 fps. 23.976 is a NTSC fps, Menaing Not HD its standard Resolution.

    BTW NTSC is Interlaced, so i dont think you would want to see the orginal image in the first place....Deinterlace that sucker.

    Unless your TV is Capable of Supporting 23 herzt i would not even try it.
     
    Last edited: Apr 22, 2009
  10. puntloos

    puntloos Member

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    You're being a bit nitpicky there. Sure, the refresh rate of the actual display hardware is fixed. I said 'TV' however, which I see as a 'black box' with input hardware that will accept video frames, and instructions of at what virtual refreshrate - if you will - it needs to play this back. What it does afterwards is irrelevant to this story.

    And uh, damaging the TV? This is not a 80's CRT :)

    Then you're lucky :)
    Let's assume for a second that the TV is capable of exactly (by interpolation, pulldown, frameskipping, whatever) playing back a movie at the right speed, averaging at the correct # of frames every second.

    Assume the movie is an hour, i.e. if it is 23.976 fps it will be 86313 frames.

    If the videocard/driver send 23.976 frames per second to the TV - and tells the TV it is 23.976,will run for an hour.

    If the videocard/driver sends 24 frames per second to the TV - and the TV renders this at 24 frames per second, the 86313 frames will last 3596 seconds.

    The problem is that the audio (which always plays exactly the same lenght, audio is frequency locked at 48Khz (for example)) will always play the exact hour, so after an hour the audio will trail the video by 4 seconds.

    Now there are setups that detect this problem and rerender the audio, slowing it down a little, then recompressing, but this is of course not desirable.

    Anyway the end result is the same: I need the nvidia driver to send 23.976 fps to the TV, not 24.
     
    Last edited: Apr 22, 2009

  11. puntloos

    puntloos Member

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    No I don't.
     
  12. puntloos

    puntloos Member

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    Modern 24Hz capable TVs do exactly that. (yes, they do the same with 23.976)
     
  13. ElementalDragon

    ElementalDragon Ancient Guru

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    There are only a handful of displays that apparently support 24hz . And the only apparent reason for needing such a thing is supposedly if you're watching BluRay/HD DVD movies. I've never seen an issue with a BluRay movie on my monitor, or on our TV.... and i've never heard of an issue with sound being out of sync.
     
  14. puntloos

    puntloos Member

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    Sadly I'm a perfectionist. Although not being able to tolerate 4 seconds out-of-sync after an hour...

    So the question stands.. how can I force 23.976 refresh rate with nvidia drivers?
     
  15. bp9801

    bp9801 Ancient Guru

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    You really can't because odds are, your monitor doesn't support that low of a refresh rate. I won't get into why you don't need the refresh rate being the same as your frames for a movie, because its already been explained. The lowest a monitor/tv can do, is a horizontal refresh of 30 hertz. As has been stated, the hertz of the tv means nothing for frames. Unless you're editing sound to a movie clip that has none, I don't see why or how your sound can be out of sync because of your hertz. Its just not really possible. I've been around tvs long enough, hertz only effect movement of the pixels.. not the frames.
     

  16. Pill Monster

    Pill Monster Banned

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    Then why are you trying to play the movies through your PC?



    But they won't be out of sync that's what 3:2 pulldown is for - partially..

    Look maybe if you had all the right equipment maybe you could do it, but you apparently don't, so you'll need to make some compromises..
     
    Last edited: Apr 25, 2009
  17. ElementalDragon

    ElementalDragon Ancient Guru

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    bp9801: i tried to basically explain that..... that the refresh rate has nothing to do with how many "frames per second" the video card outputs.... but he seems to have this odd theory that, if i understand what he's trying to say correctly, the video card sets the refresh rate of the monitor, and thus plays the video at that speed, but the audio won't necessarily be played in sync with the video then.

    Again.... like i said.... the only reason anyone mentions of needing such a refresh rate is for BluRay/HD DVD movies.... and i've played BluRay movies on my 60hz LCD monitor, and i've never noticed the sound out of sync. And perfectionist or not, you'd be a freakin idiot to not notice a 4-second sync difference by the end of a movie. You could probably be so drunk you'd believe watching paint dry is an olympic event, and still be able to notice such an A/V sync issue.
     
  18. bp9801

    bp9801 Ancient Guru

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    See, its people like him that made me leave the tv sales business. Because people have a preconceived notion of what they want the tv to do yet the technology hasn't been invented yet. I watch Blu Ray all the time on my 720p 60hz tv, its perfectly fine and I have yet to notice anything being out of sync anywhere. Now, I can do just fine with that, but getting a 1080p 120hz tv with an HDMI input of 1080/24p, then you just might notice a difference. But thats because the input is designed to handle 24 frames for a movie and the typical 60 frames. Frames does not equal hertz, like ElementalDragon said, they just don't work like how you think they do.
     
  19. Grendel_66

    Grendel_66 Master Guru

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    Not. The audio/video streams are physically linked together at the source (video disk) and will not "desync" over time, since frames are not buffered. If you worry about the video quallity, get a 120Hz TV.
     
  20. puntloos

    puntloos Member

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    Not a monitor. HDMI out -> TV that is intended to display 23.976 sources like blu-ray disk player.
    That last statement makes no sense at all.
     

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