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DVD encoding question

Discussion in 'Blu-ray & DVD Players & Recorders' started by StooMonster, Dec 6, 2002.

  1. StooMonster

    StooMonster
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    My mate Ray says that I am wrong when I think all DVDs are encoded with either 25 or 30 fps (PAL and NTSC respectively). We're just talking about US and UK discs here, no other countries.

    He believe that some "film" transfers to DVD are at 24fps, like real physical film.

    We also believe that some DVDs have data stored in progressive and the player converts to interlaced, and others are stored in interlaced format. (Or the other way round if you have a progressive player.)

    Where can I find out more information? Or does anyone here know about this stuff?

    StooMonster
     
  2. Private Penguin

    Private Penguin
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    Good question StooMonster.

    My limited understanding is that film material is always 24fps on DVDs, however different techniques are required dependant on the refresh rate of your display, e.g. for NTSC (60Hz) 3:2 pulldown and for PAL (50Hz) 2:2 pulldown.

    But then this would suggest there is no difference between NTSC and PAL discs, hmmm, I'm confused too :blush:

    I also understand that film material on DVDs is in interlaced format, therefore the above mentioned techniques are used for creating a progressive scan output, i.e. sample two fields and then output a single combined field.

    Does this make sense. Am I completely wrong. Any input would be very much appreciated.
     
  3. StooMonster

    StooMonster
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    From: Martin France (mfrance@nomail.to.me)
    Subject: Re: Question about interlacing and dvd?

    Briefly, MPEG-2 video can be progressive or interlaced. This is a matter both of encoding and (potentially subsequent) flagging. You can switch the interlace flag without re-encoding, but using the correct setting in the encoder is vital. If you are encoding interlace, then encoding as progressive will give very significantly poorer results. And if there is no interfield timing difference (the video is "progressive") going in, then encoding in progressive should give some benefit, especially at lower datarates.

    The above is true for material at 25 fps ("PAL"), 23.976 fps ("NTSC Film"), or 29.97 ("NTSC"). However, for 23.976 material, it will rarely be (correctly) flagged as interlaced (!), and you can set an additional flag for "pulldown." Such video then reports a ramerate of 29.97, and instructs a suitable decoder (such as is found in "set-top" DVD players) to add either 2:3 or 3:2 pulldown fields, depending on which type of pulldown is flagged.

    However, a DVD player capable of outputting a progressive, 23.976, frame stream (such as a software player on PC, or a standalone "prog-scan" DVD deck) can simply ignore the flagging and present the underlying progressive video.

    Here's a table of what might be found on various DVDs:

    "PAL" DVD (MPEG-2 video):

    25 fps. Progressive. No pulldown.
    25 fps. Interlaced. No pulldown.

    "NTSC" DVD (MPEG-2 video):

    29.97 fps (23.976 progressive w/ 2:3 pulldown).
    29.97 fps (23.976 progressive w/ 3:2 pulldown).
    29.97 fps. Progressive. No pulldown.
    29.97 fps. Interlaced. No pulldown.

    Now, it doesn't have to be *quite* that simple - in particular the field order can also be flagged, and the possibility exists to switch types mid clip!

    Incidentally, I haven't come on a DVD player which accurately reports the information for any particular "clip." You can rip the DVD to HD, extract the MPEG video stream(s) and then analyse them, of course.

    Hope that helps a bit....

    Marty


    Also found this...
    From: Tom Jordaan (99037613@brookes.ac.uk)

    Entirely up to the MPEG-2 encoder; MPEG-2 can handle interlaced and progressive video.

    In practice, an MPEG-2 encoder fed from a progressive source (e.g. a decent 2k or 4k transfer of film) will use frame-based encoding, while an encoder fed from an interlaced source (e.g. SDI) will use field-based encoding.


    More food for thought there!

    StooMonster
     
  4. RAMiAM

    RAMiAM
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    Yeah, that's me that is the "mate Ray" :)
     
  5. StooMonster

    StooMonster
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    Hello mate!

    Sent all my research to your email at work. Interesting stuff!

    StooMonster
     
  6. Squirrel God

    Squirrel God
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    :eek: Glad to hear it :eek: :D
     
  7. StooMonster

    StooMonster
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    I should've checked Marty France's post more closely!

    Hopefully English is his second language, if not... :eek:

    StooMonster
     
  8. kevb

    kevb
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    I have but it was an accident.:blush: Mind you It was a nice looking one.:D
     
  9. Private Penguin

    Private Penguin
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    Now that is funny :D
     

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