[mythtvnz] Ratios, Was Building a new box using an ASUS A8N-VM CSM board

[David Zanetti]

--=-pAnO02s5cox282Tq9c+R
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable

On Fri, 2006-01-20 at 17:43 +1300, criggie@criggie.dyndns.org wrote:
> Steve said
> > I've got one too, had no problems getting it working. I've also got a
> > tuner-less video capture card for Sky and with my current capture
> > settings (576x576 mpeg4 + mp3)
>=20
> This one has been bugging me for weeks.  Why do many of the mythtv howtos
> (and the default) use a 1:1 ratio of 480x480?
>=20
> Surely a 4:3 ratio like 640x480 or 320x240 would be best?

The upper limit for horizontal resolution is quite low, somewhere around
400 pixels across on a good TV. Cables (esp composite) limit this
further. And colour is even lower resolution than that.

Vertical resolution comes from the hsync, so it's more or less fixed.

When I had my PVR based on an SAA7134, I recorded everything in 352x576.
No-one seemed to notice. And if you can throw away half the pixels with
no-one noticing, it's going to improve what the encoder bitrate has to
encode.

480x480 is probably more horizontal than is possible over a cable (480
vertical is visible for NTSC), but there's no real harm in scaling it
back up to 4:3 when you can't resolve that level of detail anyway :)

--=20
David Zanetti <david.zanetti@catalyst.net.nz>
Team Leader, Systems Administration
Catalyst IT Limited
+64-4-8032233 +64-21-402260

--=-pAnO02s5cox282Tq9c+R
Content-Type: application/pgp-signature; name=signature.asc
Content-Description: This is a digitally signed message part

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (GNU/Linux)

iD8DBQBD0HALei0cZZ0ajFMRAp9fAJoDRC3O6Vc+sYMw29Uo4s8+cxwm8wCfTcGm
dze3/HhHHo+eHUxlc2uF79M=
=3r4u
-----END PGP SIGNATURE-----

--=-pAnO02s5cox282Tq9c+R--