[MPlayer-users] Question on converting to DivX4...

[Rich Felker]

On Wed, Jul 13, 2005 at 05:37:40AM -0700, RC wrote:
> On Tue, 12 Jul 2005 23:17:17 -0400
> Rich Felker <dalias at aerifal.cx> wrote:
> 
> > sounds like your sound driver has broken timing. :(
> > using -autosync 30 might help.
> 
> -nosound helps, but sadly -autosync 30 doesn't seem to...  -mc 0 also
> doesn't help.
> 
> Also, I just switched from the OSS driver I had been using, to the ALSA
> driver, and it is just as problematic (either with -ao oss or -ao alsa).
> I would expect SB Live drivers to generally be better than the drivers
> for cheap/ junky sound cards, but that doesn't seems to be the case.

:(
i wonder if anyone else has ideas..

> > 'antialising' is a method of preventing the aliasing from happening to
> > begin with. 
> 
> There are antialiasing methods like "smothing" which operate on aliased
> images.  Whether you want to call that antialiasing or something else
> doesn't really matter.

i call it something else, because it doesn't work. if it had a chance
of working i might consider calling it antialiasing too.

> It does *mask* the aliasing, which was my point.

but it doesn't. try this:
- take an image alternating between black and white every line.
- scale it to 7/8 height with nearest-neighbor resampler (this will
alias it)

there is absolutely no way any smoothing will ever reverse the
aliasing. but not only is it irreversible -- that's true even if you
scaled down in a non-aliasing way. but in this case it's also
impossible to remove the offending artifacts without also destroying
any other content in the picture.

if you want a realistic example, start with some animated content with
thin black lines, nearly horizontal but not quite (slope between 1/10
and 1/3 would be good). then use pp=li to throw away one field and
interpolate from the other. it will be horribly aliased and no amount
of smoothing will make it look at all correct again.

rich