[mythtv-users] Can I play scaled HDTV content on a standard TV?

Brad Templeton brad+myth at templetons.com
Tue Dec 7 23:10:26 UTC 2004

On Tue, Dec 07, 2004 at 04:06:37PM -0600, Lane Schwartz wrote:
> OK, I know this is a really basic question, but I haven't been able to
> find an answer in the archives....
> I'm thinking about buying a pcHDTV 3000. I currently have Myth working
> - connected to my TV via the svideo connection on my nvidia 5200. My
> processor is a P4 2.8C HT. I have a standard definition TV set. At
> some point in the future I will buy an HDTV set. In the meantime...
> Is it possible, using Myth, to watch TV shows recorded using a pcHDTV
> 3000 on an standard television set?
> I realize that if this works, I will not be viewing the recording at
> anywhere near true HD quality. My thought is that if this works, the
> quality for the HD recordings would still be better than the my
> standard non-digital cable signal.
> Maybe this is all just crazy-talk. I'd appreciate any comments, esp
> from those of you more well-versed in HDTV and TV-out downsampling
> than I am.

It can actually look pretty good.  Your P4 should be able to do it.
However, one problem I have noticed when trying this is some really
annoying interlacing artifacts when playing 1080i!   I don't believe
the P4 2.8 has enough CPU to do de-interlace on 1080i but I could be

Some tricks I have not tried yet including trying to set the tv-out mode
to be exactly 540 lines -- that might help a lot.   Many TV out cards
will go all the way to 1024 x 768.

Another approach which would work even on a slower machine would be
to transcode your HDTV down to 720x480 with de-interlace.  Aside
from giving you much smaller files it should play with a lot less
CPU and not have interlace artifacts.

No watching the show until an hour or two after it's on, though.

The output actually looks pretty good, noticeably better than ordinary
480i TV, presumably it should be full 480p (DVD) quality. 

Of course the signal will be re-interlaced if it goes out a tv-out.  I
suspect my interlacing artifacts may be coming from the re-interlace.
If you have a progressive scan EDTV, you might get less trouble there.

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