[mythtv-users] pcHDTV with PVR-350 for output

Dan Lanciani ddl5 at danlan.com
Mon Oct 25 03:47:41 UTC 2004

Daniel Thor Kristjansson <danielk at mrl.nyu.edu> wrote:

|You can't have complete independence of input and output encoding 
|without very high CPU requirements.

If "very high" equates to about twice what we have now, it shouldn't be
long before this is not a problem.  In any case, it would be nice to have
at least *some* independence...

|Which is why commercial DVRs insist 
|on computers with matched hardware encoders and hardware decoders. 

The commercial DVR I bought doesn't insist on a computer at all. :)

|But don't fret too much about FireWire/DV, a P4/1.8Mhz can cope with DV, 

Meaning that it can transcode to it from any of the on-disk formats you may
use in real time or meaning that it can only render it to a display?

|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.

I didn't realize it worked with any FireWire input; is this documented
somewhere?  (I don't care about encrypted streams; I just want to move
video among my internal devices.)

|]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.

Ah, I didn't realize that this was not supposed to work.  Does any kind
of fast forward functionality work?  Rewind?

|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

Sorry, but I really find this a bit hard to believe. :(  And even if it
doesn't look good it is the accepted way to interconnect with other non-
display devices.

|(For instance, I can get my plain old TV to sync to a 
|800x600 signal from the FX5200.)

I'm not sure what this means.  Are you actually generating 600 (300 interlaced)
scan lines?  If so that's not real NTSC anymore.  Maybe you can get a specific
TV so sync to it, but it won't work as a general video source.  And this is
my main gripe with the TV-out support on every video card I've ever tried.  You
can tweak this and that to get it to almost look right on a particular TV, but
the signal is so far out of spec that it's useless for anything else.

|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.

I haven't even noticed the ringing yet.  It is completely overshadowed by
the horrible motion artifacts.  Even as someone moves their hand across the
screen you can see lots of black scan line "checks" around the motion.  I
know it isn't a problem with the source stream because my ancient DTC-100
renders a perfect NTSC representation of the same program.  I don't know if
it is an MPEG decoding issue or an NTSC encoding problem, but it (IMHO) makes
the output useless.  (See my previous message about the FX5200.)

I'm going to keep playing for a while, but I get the feeling that what I
want (ATSC source; real NTSC out) is not possible with the current selection
of hardware and software. :(

				Dan Lanciani
				ddl at danlan.*com

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