[mythtv-users] pcHDTV with PVR-350 for output
Daniel Thor Kristjansson
danielk at mrl.nyu.edu
Mon Oct 25 02:36:14 UTC 2004
]Then if I were watching an ATSC program and tried to start a recording from
]Svideo in (or a tuner) on a dumb capture card one or both would likely fail
]on a single P4/3.2GHz?
You could use nuppelvideo for the frame capture card and it should work.
But using mpeg-4 would probably be a bad idea. Most commercial PVR
software doesn't support using frame grabbers. (Hardware MPEG-4 capture
cards still cost lots-o-money.)
]I'm looking at what it would take to have a general solution that will
]support the same kinds of features as commercial DVRs, but of course without
]annoying copy protection mechanisms. Independence of input and output encoding
]is also important to support FireWire/DV. If the required CPU power if just
]out of reach today on a single processor machine it will probably be well
]within reach in a year on a dual processor machine.
You can't have complete independence of input and output encoding
without very high CPU requirements. Which is why commercial DVRs insist
on computers with matched hardware encoders and hardware decoders.
But don't fret too much about FireWire/DV, a P4/1.8Mhz can cope with DV,
and FireWire HDTV won't require any more decoding power than
over-the-air HDTV. The biggest obstacle will be encryption, as the FCC
is allowing cable operators to encrypt FireWire video. MythTV will not
work with these as inputs.
]As far as cheap (or even expensive) video cards with TV-out, my experience
]hasn't been good, but I'll certainly give it another try. I already have the
]FX5200, though I've noticed that fast-play doesn't actually work (it shows
]little spurts of fast motion, but generally gets behind). I don't know if
]that is a video card issue. I'd really love to just feed DV to a Sony DVMC
]or Miglia decoder since they produce nice NTSC timing.
We can get fast-play working with HDTV, but it's not yet high priority.
It's mostly a ffmpeg w/MythTV issue. I don't think anyone is working on
DV out, DV looks pretty crappy compared to what you can do with a good
TV-out setting (For instance, I can get my plain old TV to sync to a
800x600 signal from the FX5200.) The problem with the nvidia output
stage is the analog filter, it has too few taps and produces some
ringing around edges in the image. You can reduce or eliminate this by
using a higher output resolution than your capture resolution.
For reference, in terms of CPU requirements (low to high):
nuppelvideo enc, nuppelvideo dec, DV enc, mpeg2 dec, DV dec, mpeg4 dec,
mpeg2 enc (480i on a P4 at 3Ghz, 1080i on $10,000 hardware encoder.)
mpeg4 enc (480i on a P4 at 3Ghz, 1080i on $100,000 hardware encoder.)
You can make mpeg encoding faster by doing a worse job of it, like
"Quicktime Pro" does, but even so it demands a serious processor.
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