[mythtv-users] NVidia non-interlaced video output quality-loss?

[steve at nexusuk.org]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Sun, 15 Feb 2004, Thomas Börkel wrote:

> Sorry, typo! I meant 352x480. I thought that analog TV only has half the 
> possible horizontal resolution.

I've not used analogue TV for a long time, but the luma signal is 
reasonably high res whilest the chroma is very low res...  (The idea is 
that the human eye is far more sensitive to light and dark than colour, so 
reducing the resolution of the colour isn't very noticable except for a 
minor amount of colour bleeding over sharp boundaries).

A bit of Googling later... :)
PAL-I (what we use in the UK) gives you a picture that's 572 pixels wide 
but only with 461 pixels of colour.
NTSC gives you a picture that's 442 pixels with 377 pixels of colour.

>From what I can tell, in the UK the digital channels use either 704 or 640 
pixels wide (not sure which).  I receive my TV through a Sky Digital 
satellite decoder, which is plugged into my Myth box using S-Video and I 
capture at 640x576.  Leads to pretty good quality all round (I'm limited 
to 640 pixels wide because I'm doing software MPEG4 encoding and don't 
have a meaty enough CPU to go higher if I want to be able to watch at the 
same time).

> OK, thanks. I am curious, how it will look (buying my MythTV box 
> components next week).

Start with deinterlacing turned off in Myth itself - since the nVidia card 
will deinterlace then you don't need to do it twice.  Deinterlacing does 
have the advantage that you don't have to worry about the sync - if you 
have an interlaced picture then you have to make sure the display is 
updated at the right time, otherwise it displays the fields in the wrong 
order which is really horrible.

I often wonder if it would be better to record and play back the fields 
separately (i.e. record and play a half-resolution movie at 50fps instead 
of full resolution at 25fps).  That way you could guarantee teh field 
ordering would be correct, and you'd still retain all the data from both 
fields...  but it'd probably strain the CPU a lot more to keep up a 
constant capture and playback at 50fps.

- -- 

 - Steve                                             http://www.nexusuk.org/

     Servatis a periculum, servatis a maleficum - Whisper, Evanescence

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.3 (GNU/Linux)
Comment: Public key available at http://www.nexusuk.org/pubkey.txt

iD8DBQFAL2TB5zUOsIV3bqERAoWBAKCqK1UO1Bi4TsmEPkppvuqw+BB0rgCgnxiT
BO++fx/Tpgc6KAbF2lifFwM=
=/OeE
-----END PGP SIGNATURE-----