[MPlayer-users] Changing aspect ratio within DVD title

Oliver Fromme olli at lurza.secnetix.de
Mon Aug 11 14:31:14 CEST 2003

Adam Nielsen wrote:
 > I've also seen DVDs that do this.  It should in theory be possible, because 
 > the aspect ratio is encoded into the video, but I imagine it would require 
 > extensive modifications, which are probably not worth it for the small number 
 > of titles that make use of it.

That's what I was tinking, too.  It's a pity, though.

 > Have you instead tried finding the exact locations of the aspect ratio switch?

That would require a lot of trial-and-error, because mplayer
doesn't have a function to step forward frame-by-frame (that
would be _extremely_ useful!).

That's why my idea was to convert the title to a series of
JPEG images (mplayer supports that with the -jpeg option).
Then it would be very easy to find the locations.  Then I
could scale those JPEGs, add black bands, and then encode
the whole series of images with mencoder.

 > Then you could just encode each section manually, e.g. encode the first 
 > minute as 4:3, then encode the next minute as 16:9, etc. then just join all 
 > the files together at the end.

Uhm ...  I've never tried to join AVI files.  The "transcode"
package contains a tool called avimerge, but I'm not sure how
well that would work.  I guess that the parts must have the
same resolution and aspect ratio, so I would have to scale
the 16:9 parts and add black bands appropriately.

Has anybody tried that before?  Any caveats?  Would it be
indeed easier than the JPEG images approach above?

(I would just prefer to avoid re-inventing the wheel, or
spend an afternoon finding out that it doesn't work.  But
I'll try if nobody else has any experience on this.)


Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
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