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

[Aran Cox]

On Wed, 2003-09-24 at 02:20, John Morris wrote:
> On Tue, 23 Sep 2003, Chris Petersen wrote:
> 
> > > But in any case, adding " -aspect 1.33333" to
> > > the bitrate prompt tells the encoder to specify 4:3.
> > > If you are asking if it should be hard coded into
> > > the script, it'll squish HDTV but I'm not sure
> > > that anyone is using nuvexport with HDTV (yet).
> > 
> > The aspect ratio should be encoded into the nuv file, and the nuv_info()
> > function should be able to get at it.
> 
> 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.  

mplayer/mencoder can put an aspect ratio into an avi file, but no
program but mplayer/mencoder (at least according to the docs) will be
able to interpret it.  You can write the aspect into a file by using the
-lavcopts aspect=4/3 option in mencoder.  But of course, nuvexport uses
ffmpeg.  

You can also use resolutions that are close to 4:3 like 400x304.  You
could use 400x300, but I've heard recommendations that you stick to
height and width that is a multiple of 16.  (hence 304, instead of 300)
I've had good luck using close enough values to 4:3 for when 320x240 was
just to small and 640x480 was just too large.