[MPlayer-users] Changing aspect ratio within DVD title

Oliver Fromme olli at lurza.secnetix.de
Mon Aug 11 10:45:22 CEST 2003


First of all, I did RTFM and searched the list archive,
although the latter was a bit difficult, because I wasn't
successful in finding the right words to search for, so
I either got zero hits or a thousand ...

I've been using mencoder for quite some time to convert
DVDs to mpeg4 AVIs with great success (3-pass mode, with
subtitles, even with multiple languages and what-have-you).
It's a very handy and powerful tool.

However, recently I stumbled across two DVD titles which
caused problems.  Encoding went well, but when I looked at
the resulting AVI file, some parts of it seemed to be
distorted.  You know, that "tall/skinny" effect when you
scale a 16:9 video to 4:3.  I was a bit confused, because
I had encoded titles with various aspect ratios before
(4:3, 16:9, 1.85:1, 2.35:1) without any problems.

It turned out that those particular DVD titles were
changing the aspect ratio in the middle!  Obviously,
mplayer and mencoder are not able to handle that,
unfortunately.  For example, one of the titles starts with
4:3 and plays fine for a while.  It is off-stage footage of
a band, intermixed with interviews with the band members.
When the first interview begins, the aspect ratio changes
to 16:9, but mplayer (and mencoder) still handle it like
4:3, so it comes out distorted.

This not not really a bug report, because I think it would
be _very_ difficult to fix.  So I don't really expect it
to get fixed.

Anyway, my question is:  Does anybody happen to have an
idea how to work around the problem?  Well, I considered
converting the titles to a series of JPEG images, find
the intervals with changed aspect ratio, scale them and
add black bands (small shell script + netpbm tools), then
encode the whole bunch to mpeg4 AVI.  It would certainly
work, but there must be an easier way.

Any ideas, hints, suggestions etc. are very welcome!


PS:  If it helps, I would be willing to make the shortest
of the DVD titles available to a developer (via the net or
on CD-R).  It's about 7 Minutes of DVD video.  I can also
provide any debug output or what ever might help.  Just
tell me what to do.

PPS:  Yeah, I know it's customary to provide output from
mplayer -v etc., but as I said, this is not really a bug
report, and I don't think it would help.

PPPS:  Interestingly, my standalone DVD player handles
those titles differently from normal 16:9 titles (where it
adds the usual black bands).  When the change from 4:3 to
16:9 appears, it does not add black bands, but removes part
of the video at the left and right (i.e. it "zooms in", so
to speak).  I guess the reason for that behaviour is that
it doesn't have to change the decoded signal, because it
stays at 4:3.

Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
Any opinions expressed in this message may be personal to the author
and may not necessarily reflect the opinions of secnetix in any way.

"Ich bin weit über die Fähigkeit rationalen Denkens hinaus entsetzt."
        -- Ray (Ghostbusters)

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