Re: [dvd::rip] Re: Deinterlacing

Brian J. Murrell wrote:

On Mon, 2005-07-25 at 19:35 +0200, Sylvain wrote:

It seems to me that when watching a movie on a computer screen,
interlaced frames are visible and not too pretty.


For most movies, this should not be the case if the player is any good.
Most movies are shot on film and therefore progressive in content.
However, when they are mastered to a DVD in mpeg2 format, they are
interlaced (i.e. converted from progressive to interlaced) using a
technique called 3:2 pulldown.  This can be soft or hard.  Soft is just
a flag in the MPEG stream telling the player to do the interlacing and
hard is where the actual content on the DVD has been put through the 3:2
pulldown.  I'm not sure I can think of a good reason for the latter
though.

A decent player on a progressive display (like a computer monitor)
should be able to detect this artificial interlacing of non-interlaced
material (i.e. progressive material interlaced with a 3;2 pulldown) and
"undo" the interlacing and return it to it's native format (24fps
progressive scan in NTSC/north america).  mplayer is smart enough to do
this.

(If I'm recalling this correctly) In fact with MPEG2, the interlacing on
the DVD can (and IMHO) should be artificial in that the DVD is simply
flagged as "should be interlaced" and the DVD player is what does the
interlacing on the way out to the STDV.  The actual stream should be
progressive still.  mplayer does this when it detects that a 3:2
pulldown (artificial interlacing) is called for:

demux_mpg: 24000/1001fps progressive NTSC content detected, switching
framerate.

But then, why are deinterlacing method so cpu intensive ? if I understand correctly, they just have to ignore a flag ?
Or are some dvd "artificially interlaced" and others "really interlaced" ?

And indeed, my tests on mplayer playing a VOB file from a film does
indicate that there is no interlacing going on.
And indeed, a DVD player outputting to a progressive display should not
do the artificial interlacing and should just present the original 24fps
progressive content unaltered.

So with a good player, if you are seeing interlacing artifacts, the
source material was probably recorded on video tape originally and
interlaced at that point.

"mplayer dvd://1" with no option sure show me an interlaced video with my "Abyss" dvd, while everything is fine with "Apocalypse Now" as an example. Same with xine.
Sometimes, on the same dvd, the movie is not interlaced when I play it using mplayer, while the bonus are.
Is it because of the original recording ?

Still, and I should indeed have mentionned it in the firt place, that
may vary from one screen to another, and on a TV set I can hardly see
interlaced frames (this may because I'm generally further from the
screen).


Not at all.  A TV displays interlaced material interlaced.  You should
see no interlacing on a TV at all.  If you do, then some processing
between the source and the destination screwed up the interlacing.

You're right, when I look at it closer, what I thought was interlacing is just normal imperfection (a little "lag" on the screen).

Anyway, thanks for the whole explanation :)

And I don't know what pvr and SDTV are so I'll take your word for it.


SDTV == Standard Definition TV.  i.e. 720x480 interlaced.  PVR is
Personal Video Recorder.  i.e. MythTV.

b.