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Thread: how can I tell if I need inverse telecine (24fps)?

  1. #1
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    how can I tell if I need inverse telecine (24fps)?

    I got a .TY, and once encoded to an SVCD 29.97fps .MPG using TMPGEnc, I notice when I use PowerDVD and advance frame by frame manually, I see the video has 4 frames of movement, but the 5th frame is a duplicate of the 4th. So the sequence is like 1234456788...etc. And you can see the duplicate frame as a frame pause while playing.

    But if I encode with TMPGEnc using the "inverse telecine 24fps" option, every frame has movement, and it plays smoothly.

    So I guess this means that this .TY requires inverse telecine encoding?
    Is there any method to know which .TYs require IT?
    Or is the method of encode-and-see-for-yourself the only way?

  2. #2
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    Some pieces of software have a "detect 3:2 pulldown" - which is the method used to make a 24fps film "work" in 30fps (er, 29.97, darn those drop frames) video.

    Generally speaking, any movie that you're capturing probably *will* have 3:2 pulldown. Anything shot on video most likely will not. Anything shot on film (e.g. West Wing) ... you might have to go check.

    I've never used TMPGenc (or the plus version), so I don't know if it has the ability to autodetect 3:2 pulldown in the source.

    Maybe displaying this sort of information might be a useful add-on to tytool/tystudio?

  3. #3
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    Well in messing around, I've found that DVD2AVI will load a .ty file. Very very crude and not really supported, but it'll open it right up and show you when your video changes to 24fps, 30fps, interlaced, progressive... Not too accurate, but you get an idea.

  4. #4
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    Originally posted by Pro-289
    Well in messing around, I've found that DVD2AVI will load a .ty file. Very very crude and not really supported, but it'll open it right up and show you when your video changes to 24fps, 30fps, interlaced, progressive... Not too accurate, but you get an idea.
    Doesn't mplayer w/ ty support do this also (at least to the console)?

  5. #5
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    I wouldn't know. I've only found Linux versions of Mplayer. But I'm using WinXP.

    Anyone know what a windows guy could do to play Tys and see a bit more technical details?
    Last edited by Pro-289; 07-23-2003 at 12:01 AM.

  6. #6
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    Re: how can I tell if I need inverse telecine (24fps)?

    Originally posted by Pro-289

    Is there any method to know which .TYs require IT?
    Or is the method of encode-and-see-for-yourself the only way?
    In TMPGEnc, instead of just checking "inverse telecine" you can double click it. That will bring up a tool that will let you see the effect with the processing on and off.

  7. #7
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    Alright, so I guess encode-and-see-for-yourself is the only way for a windows user then.

    I like that I can use DVD2AVI directly on a .TY to see before I even think about converting it to an Mpeg, but it's not accurate, and I found a .ty it wouldn't even load.

  8. #8
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    Inverse Telecine (more than you ever wanted to know)

    Wow. Finally, a subject I know something about.

    Here's a little primer about film, video, and telecine.

    Film is shot at 24 fps. NTSC video is 29.97 fps. In order to transfer film to video 3:2 pulldown is used. Basically, frame 1 is transferred to the first 2 fields of video, frame 2 goes to the next 3 fields, frame 3 goes to the next 2 fields, and so on. When you view the video frames frame by frame it's likely you're only looking at a single field - this results in the 4 unique frames / 1 repeated frame thingy. While it looks like this you're actually seeing a 3 field, 2 field pattern. But anyway...

    Stuff originated on video has not been telecined. Nor can it be. So it can't be inverse telecined.

    Obviously, given the limited space on a dvd, it is desirable to put as little information on there as possible. Since the 3:2 pulldown introduces redundant information to pad out the 24fps film, on many dvds the true 24fps stream is recorded and it's left to the player to add the pulldown. This reduces the file size considerably.

    So reverse telecine is desireable for film based stuff.

    HOWEVER

    If a production was never intended to be screened theatrically it's unlikely that a finished negative was ever prepared. This negative is what would be transferred to video for the final video release. It's called "Film Finishing" Basically the pulldown occurs as a repeating pattern from the beginning to the end of the film.

    On a film based TV show, like West Wing, the post production process is as follows:

    Shoot show on film
    Transfer all the film to video (adding pulldown)
    Edit the video into the final show.
    Broadcast.

    Here's the problem: When you cut from various reels of film transferred to video there is no guarantee that you're going to be grabbing each segment at the same place in the pulldown pattern. In fact it's highly unlikely. So the pulldown might go 3:2:3:3:2:2:3:2:3:2 etc. What this means is that the auto inverse telecine tools won't work because the cadence changes at each cut. Just imagine what happens during a dissolve from shot A to shot B with differing cadences in each....


    So. Use inverse telecine on feature films. Don't bother on stuff that's video cut or, even worse, shot on video.

    And you'll have a hard time on a feature that's got commercials in it, too.

    Hope this helps.

  9. #9
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    Re: Inverse Telecine (more than you ever wanted to know)

    Originally posted by micktravis
    Here's a little primer about film, video, and telecine.
    Great explaination.
    Thanks for the input.
    It's a bit clearer now.

  10. #10
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    Dont' forget that NTSC DVD players expect the full framerate, not 24 fps. To fix this, use pulldown.exe from doom9.org
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  11. #11
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    Originally posted by FredThompson
    Dont' forget that NTSC DVD players expect the full framerate, not 24 fps. To fix this, use pulldown.exe from doom9.org
    So if a DVD did have 24fps, would it require one of those DVD players that advertise they do automatic 3:2 pulldown?

  12. #12
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    No, use fixpulldown.exe (sorry, I typed pulldown.exe earlier) which you can find at doom9.org to modify the header of your MPEG2 so it will work in a standalone NTSC player. I do that a lot with captures of film. It gives you more bandwidth per frame. If you've got a really odd framerate, like some early film, there are special decombing routines.

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