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

[Rich Felker]

On Mon, Jul 11, 2005 at 09:24:09PM -0700, RC wrote:
> On Mon, 11 Jul 2005 12:23:55 -0400
> Rich Felker <dalias at aerifal.cx> wrote:
> 
> > Compute the number of possible frames, and the number of possible
> > outputs of pp=lb.
> 
> I must admit, I have no idea what you're trying to say here...

the number of possible frames is 2^(bpp*w*h).
the number of possible frames pp=lb can output is much smaller, but a
pain to actually compute.

> 60fields/sec vs. 30fps isn't vastly smaller, IMHO.  But more
> importantly, the frames are double the height of the fields, so
> basically two are being assembled together.

they're only double height because you destroyed a huge amount of
information.

> > My guess is that the timing on your computer is very bad.. Maybe bad
> > ao driver? Does the problem go away with -nosound?
> 
> Well, damn.  You're right, -nosound helps tremendously.  It still
> doesn't look like live TV, but that's taken care of the major problem.
>  I'll keep working on it.

sounds like your sound driver has broken timing. :(
using -autosync 30 might help.

> > One field _really_ is offset by half a scanline from the other.
> 
> Of course, but each field is getting upscaled from 240 to 480, so that
> should be providing some basic interpolation.

i don't follow what you're claiming here.

> > no, you just don't know what aliasing is... aliasing is basically
> > impossible to mask once it's there.
> 
> So aliasing isn't the process by which smooth curves and other
> lines become jagged because the resolution of the graphics device or
> file is not high enough to represent a smooth curve?

ok, not a really sophisticated explanation but you're essentially
right. blurring one aliased picture together with another does not
remove the aliasing though. :)

> And antialiasing methods don't exist?  

'antialising' is a method of preventing the aliasing from happening to
begin with. once a sampling is aliased there's no way to reverse it
(barring heuristic methods). normally antialiasing involves sampling
at a much higher rate (smaller interval) and then performing
filtering/resampling to remove the detail too small to be represented
on the destination device so that it doesn't alias.

some foolish people also use 'antialiasing' to refer to the process of
blurring jagged edges (video card manufacturers are particularly
guilty of this), but it's incorrect most of the time.

rich