[mythtv-users] Re: Question about nuvexport & transcoding in general

[Dennis Lou]

From: Chris Petersen <lists at forevermore.net>
>The aspect ratio should be encoded into the nuv
>file, and the nuv_info()
>function should be able to get at it.

Oh yeah.  Forgot you read in the NUV header now.

However, thinking it through, moving the aspect
ratio straight across from the NUV header
isn't going to help the case where the user 
specifies a resolution ratio that conflicts
with the NUV's pixel aspect ratio.  For example,
if mythbackend recorded at 480x480 and nuvexport
re-encodes to 480x480, then moving the pixel
aspect straight across will display 640x480.  But
if nuvexport re-encodes to 240x480, then it'll
be squished.  An 8:3 pixel aspect is what's needed
to display 640x480.  Sounds like a bit of math
is involved.  And that still doesn't solve the
Windows Media Player problem described below.

Unfortunately, I'm busy trying to repair a crashed
Windows box right now, so the patch will have
to come later.

From: John Morris <jmorris at beau.org>
>AVI has no way to encode an aspect ratio and
>when DIVX is carried inside
>AVI instead of NUV it also lacks a way to
>specify non-square pixels.  If
>you want good portable divx files you have to
>stick to encoding at
>resolutions that produce square pixels.  That
>means for normal 4:3 NTSC
>video you want 640x480 or 320x240.  

The first part is not true.  You can specify the
pixel aspect in an AVI.  However, DivX v5.05 on
Windows Media Player ignores it and assumes
square pixels.  I just nuvexport'ed an AVI
with 4:3 pixels with the aspect ratio encoded.
MPlayer played it correctly.  Windows Media Player
squished it.

However, the rest of what you said holds true:
For best portability, make square pixels.

From: Aran Cox <spin at avalon.net>
>mplayer/mencoder can put an aspect ratio into an
>avi file...
>But of course, nuvexport uses ffmpeg.  

ffmpeg can do it too.  However, for it to be
useful, nuvexport will have to do a bit of math,
as I described above.

-Dennis

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