[mythtv] Feasability of using software scalers in mythtv videoout

Steven Adeff adeffs.mythtv at gmail.com
Thu May 11 20:26:27 UTC 2006

On 5/11/06, Ed W <lists at wildgooses.com> wrote:
> Hi
> >Ignore the jpeg artifacts, the pngs were a meg each, but note how much
> >better picture quality you can get with the software scaler.
> >
> >
> I only have a standard def TV, but I did similar experiments using
> mplayer's software video output and came to the same conclusion as you.
> Lanczos and bicubic splines are a pretty decent step up in quality
> giving a sharper image (which doesn't look artificially sharpened).
> Theoretically Lanczos is a mathematically more correct scaler (ie nearer
> optimal), but in the literature it's often considered to be slightly
> bettered by bicubic splines apparently because the artifacts (such that
> there are) are more pleasing to the eye.  However, to my eye both were
> excellent and Lanczos was slightly sharper.

the problem comes with poor input signal where bicubic's softer
scaling produces a more pleasing picture. Lanczos though works wonders
with HDTV and DVD feeds because they are so clean.

> A good while back I hacked the software scaler in Myth to work for live
> tv and although I didn't persue it to the point that it would play tv
> smoothly it was clearly far better quality than the XV resize on my
> NVidia 5200 card.
> MPlayer would be a good point to start to examine the software playback
> scalers since nothing is allowed into the mplayer code which has the
> slightest bit of fat on it, so I should think their implementation is
> pretty decent.

mplayer's scalers err on the side of speed. There are better scalers
out there, but they are not really intended for real time playback,
more so for transcoding where fps isn't a concern. That said, they are
only marginally better than the mplayer implementation, so for MythTV
purposes, using mplayer's scalers are probably the best bet.

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