Posted by jag on 04/15/06 18:21

In alt.video.dvd Jan B <nospam@nospam.se> wrote:
: On Sat, 15 Apr 2006 12:01:15 -0400, "~P~" <bmxtrix2005@cox.net> wrote:
:
:>??? - You are saying that film isn't stored on DVD at 480/24i?
:>
:>This goes in direct contrast to what the link YOU provided states and which
:>I quoted.
:>
:>I am not sure what the MPEG2 header says - or what that has to do with what
:>is actually put on the disc itself - do you have any links or quotes from
:>articles that has something to do with the header - since the very detailed
:>page you linked to doesn't talk about the header at all. I can assure you
:>that DVD players pull off the frames in a flagged sequence that is
:>specifically called 3:2 pulldown or 2-3 pulldown (depending on where you
:>read it). Either way, this work is performed by the DVD player processing.
:>It is not encoded on the disc this way, it is just flagged as 24fps based
:>material and requires 3:2 pulldown to be performed. A progressive scan
:>player must go even further to recombined the frames with inverse telecine.
:>None of that is on the DVD natively, but is flagged, then performed by the
:>DVD player.
:
: Now, I'm confused.
: I thought this discussion was which of the two possible encoding
: schemes is used for 24Hz material on a 60Hz DVD:
:
: Call the 24Hz Film sequence
: Frame 1
: Frame 2
: Frame 3
:
: I see the two possibilites for DVD encoding:
: 1) No repeated frames are stored:
: Frame 1 field 1
: Frame 1 field 2
: Frame 2 field 1
: Frame 2 field 2
: Frame 3 field 1
: Frame 3 field 2

This is one possibility. Two flags (I forget their exact names atm)
specifies whether to repeat a field etc. to create an framerate of 30
frames/sec. This is a trivial task. This method is pretty much the same
as same as storing 480p, and if I remember correctly the individual
frames might actually be stored as progressive frames in the stream
rather than interlaced fields but the stream is still flagged as
interlaced per DVD specs. It really doesn't make much difference though.

: The DVD player creates 60Hz by duplication (a rather simple task) the
: sequence below ...
:
: 2) The sequence to output is already encoded on the DVD:
: Frame 1 field 1
: Frame 1 field 2
: Frame 1 field 1
: Frame 2 field 2
: Frame 2 field 1
: Frame 3 field 2
: Frame 3 field 1
: Frame 3 field 2

This is of course also a possibility but then the two flags mentioned
above are not set since the appropriate number of fields are already
present for 60i output without the need for any repetions.

: So which one is the one beeing used?

Both but the first one is superior because of better bandwidth
utilization.


J
--
"I'd give my soul to be where I was a year ago...
....if I had a soul left to give"

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