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Detection of Non/Progressive DVDs

Discussion in 'Projectors, Screens & Video Processors' started by aki, Jul 29, 2002.

  1. aki

    aki
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    Is there any software utility that with give information about the DVD video in particular whether the DVD is progressive or not (most R1/R2 Hollywood DVDs are but many are others are not) – I need to find a way of detecting if the video on a DVD is progressive or not? Or am I looking for something that doesn’t exist?? :blush: :confused:
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    At present I don't believe there are ny DVD's that are encoded progressively. Of course, that doesn't mean to say they cannot be de-interlaced and output progressively by a suitable DVD player or video processor

    Gordon
     
  3. aki

    aki
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    OK let me rephrase or confuse issues more :clown: What I need to know is ways of detecting if the video on DVD is mastered from film or from a video source. By film I mean from a progressive 24fps encoding and video 30fps interlaced encoding. Often I see DVDs that are naturally from film but have been mastered using video mode ie non-progressive (extreme example would be say Gladiator is film based, but someone has used a VHS as source for DVD). Is there anyway of detecting which source type is used? Am I making sense or am I one confused nod? :blush:
     
  4. museumsteve

    museumsteve
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    I may be talking rubbish but isn't this what the Iscan does. It has a film indicator that detects a 'film' signal..I'm sure Gordon can explain it better..:)
    I have an Iscan and the little blue light comes on from time to time..;)
     
  5. RAMiAM

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    just thought I would chip my 2 pennies worth in.

    My understanding is that all PAL DVDs are encoded using 25 fps and all NTSC DVDs are encoded using 30 fps (actuall 29.97).

    The difference between progressive or interlaced is in easy speak how the picture is drawn on the monitor.

    Interlaced draws one set of even numberd lines and then one set of odd numbered lines to give a complete picture every 30Khz (actually 31.468 for NTSC and 31.254 for PAL).

    Progressive draws the complete picture in one go every 60Khz (actually 62.94 for NTSC and 62.50 for PAL)

    Actually reading back by message the scan rates I have quoted may be double what they should be - It's been a while since I used this stuff - I'll check and send another post if it's all wrong.

    If someone else has some input - much appreciated.
    I'm getting old and it's getting harder to remember technical gumph.

    RAM
     
  6. RichardA

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    ALL DVDs are compressed in interlace 59.94Hz or 50Hz, none are encoded on disk as true Progressive scan.

    There is a 'Flag' embeded within the bitsream that is supposed to indicate whether the original material was scanned from a Filmic source (i.e. one where both fields relate to a single frame) or a video source (where each field is independent of any other).

    However these flags are not always set correctly during the authoring of the disk (Dr Who TV series is a classic) so external de-interlacers have to use other methods to determine whther the source material is filmic or not, and switch de-interlacing methods accordingly. This is what is happening on an Iscan when the 'film' led comes on - it's indicated that it reckons it is seeing a filmic source.

    Most Progresive scan DVD players use this dynamic analysis of the signal to work out what to do rather than rely on what's on the disk. PC systems I'm not so sure about, but most probably use the disk flags.

    The difference in 'quality' of de-interlacers and scalers usually comes down to how reliably they can detect filmic material so the methods used are not likely to be widely discussed (we don't want to give away our secrets!)

    Those who attended Gordon's original event can certainly attest to the variations available.

    Hope this helps.


    p.s. RAM,

    I think you are getting your field, frame and line rates muddled up!

    PAL is 50 fields per second (or 50Hz) and 25 frames per second (or 25Hz)
    NTSC is 59.94 fields per second (59.94Hz) and 29.97 Frames per second (29.97Hz)

    De-interlaced (i.e. progressive scan) outputs a frame in the same period as the original fields (so for 'PAL' progressive that is now 50 frames per second, 'NTSC' 59.94 Frames per second) To acheive this the time for each scan line halves (and therefore the frequency doubles) so for normal interlace the line frequency is about 15.625KHz for PAL (15.75KHz for NTSC) and for de-interlaced it's about 31.250KHz for PAL (31.5KHz for NTSC)
     
  7. Chris Bellamy

    Chris Bellamy
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    RichardA,

    Whenever I see people discuss deinterlacing film-based material on Region 2 dvds they talk only about 2:2 pulldown, because the orginal 24fps film has simply been speeded up in telecine transfer to 25fps and 2 fields generated per film frame.

    However, I read (in Dominic Case?s book on post production film technology) that most modern telecines can run film at 24fps and use a framestore to insert additional fields to make up the correct frame rate for tape. Every 12th frame of film is recorded onto 3 rather than 2 consecutive video fields.

    Presumably this would be a more complex scenario to present a deinterlacer, since every ½ second the relationship of video fields with film frames changes step. Are any/many films transferred to dvd/video in this way? If so, are most deinterlacers advertising 2:2 pulldown likely to be able to properly deinterlace this sort of telecine transfer strategy?

    Hope the question makes sense,

    Regards,
    Chris B.
     
  8. RichardA

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    Chris

    Yes, all Telecine machines can run at 24 fps(or 23.97Hz), and the common method to get 59.94Hz for R1 disks is to add an additional repetition of a field on alternate frames (i.e. the 3:2 bit) however I'm not aware of any disks or systems that add an additional frame to fill up the "missing" 1 in 25 fps.

    With this system you would find the video going slightly fast relative to sound and then hopping back each second (or half second if a field was inserted)

    For a reasonable de-interlacer (i.e. one with a very fast recovery time) it would detect 2:2 correctly for most of the time but would fall back to video mode around the additional field/frame - this would cause a repeated change in apparent resolution in the image and would be rather distracting.

    There are disks out there that have standards converted 24Hz to 25Hz so that the sound is correct, but they have used fairly ordinary converters that confuse most scalers (as the field relationships fall apart) - the Talking Heads disk is one, I believe.

    Interestingly in Japan they use 30fps film and convert to 60Hz 2:2 pull-down for TV programming and adverts intended for TV release rather than 24fps and 3:2 to 60Hz due to the visibility of stutter in 3:2!

    Anyway, I hope this is of interest.
     
  9. Chris Bellamy

    Chris Bellamy
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    Thanks, Richard, much appreciated.

    Maybe what the book is describing is the 'fairly ordinary converter' such as you mention.


    Chris B.
     
  10. RichardA

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    Further to my earlier reply about putting in an additional frame in every second of film to go from 24fps to 25fps.

    With some more investigation, I've found a couple of references to this technique, but it is extremely rare and seems to be confined to Australia. In fact this issue recently came up on one of the pro-cinematography sites and Dominic himself was advocating not using this method!
     
  11. Chris Bellamy

    Chris Bellamy
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    Thanks again for taking the trouble, Richard. Very interesting.
    Reading Dominic Case's book has certainly given me new insight into the complexity of post-production work,

    Chris
     
  12. MJS

    MJS
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    Richard, Chris,

    The 24/25 fps 'extra frame' issue is alive and well I'm afraid. Film editors often make a 25fps offline tape for viewing on standard beta SP or vhs decks and the technique used is simply to repeat every 24th frame once. The result is material that effectively runs at the correct speed when viewed at 25fps. As these are offline edits - they're normally compressed images produced by something like an Avid editor, they're of rather low quality and simply used to work with when producing the final version. I'm sure I have more than a couple of DVD's where the supplemental material includes the offline stuff that didn't get used in the film and you can see the effect quite clearly.

    The trouble is sometimes you only get the 25fps offline to work with and then you're reduced to cutting out every 25th frame to work with it at film rate - but that's going off topic now....

    I hope this is of interest,

    Mark.
     
  13. Mr.D

    Mr.D
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    The 24fps transfer to 25fps video (with the extra frame generation) is to enable the EDL (edit decision list) to translate correctly back to the 24fps film material for final neg cut ???

    So its not got much milage in the real world? Actually 4MC are advertising a 24fps telecine service to avoid speedup in there front window on Wardour Street at the moment...I think. Not sure what use that would be ..pop promos maybe??
     
  14. RichardA

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    Hi Mr D,

    Indeed 4MC are advertising 24fps telecine in their window, they call it Slow PAL - but I believe it's a little different to the mentioned 24 to 25 fps.

    The concept 4MC are putting forward is for US compatibility, work can be done in the 24fps world, and when converting to NTSC or HD then 3:2 is added and no need for standards conversion. The signal path for 'Slow PAL' is 625/48Psf using modified players etc...

    But, when I get back into the office I'll have a closer look at the literature I picked up from them last week to make sure I've got the story correct!


    EDIT: Having checked 4MC's literature, what they are advocating is telecine to PAL (i.e. with the 4% speed up) do any work in the PAL domain (restoration etc..) and then play out on a modified machine at 24fps through a 3:2 inserter and into a NTSC machine.

    With Telecines, they tend to use frame count rather than timecode so I guess that an offline edit using frame count would still be OK for the on-line at PAL, but it would certainly be a bit problematic is using timecode!
     
  15. Jonny B Goode

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    I think I know what your getting at. You want to know if say for example a feature film is mastered for the DVD directly from the film source or is it mastered from a source that has already been put onto video first.

    I'd imagine some older films, that get put out as vanilla releases by minor companies could well have been mastered from an old video source that could be over 10 years old.

    The answer is, you must guess.
     

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