[mythtv-users] HDTV on Myth -- is it a "myth?"

Brandon Beattie brandon+myth at linuxis.us
Mon Oct 11 16:50:51 UTC 2004

Just a couple thoughts/comments.  The ratio of HDTV to regular TV myth
users is much smaller, I'd say less than 3%.  Most people on these lists
also only stick around while they are having problems.  Also, once most
people get their HD setups working they drop off the list and go on with
life.  I think there are only 30 or so people who use HDTV that are on
the list here, and many are read only people.  Your problem is not
unique, it's just it takes time to track down the problem.  HDTV takes a
lot of resources and every CPU, MB, and hard drive will effect things.
I run 3 HDTV tuner cards and record about 20 shows a day.  My backend
hasn't crashed in 2 weeks (Before that cvs update it was every 1.5 weeks
or so).  There was a several week period where even I had problems
getting playback working well.  After a year of completely despising it,
it has since become my friend.  I run an athlon 2600 and 333mhz FSB, and
an nvidia fx5200.  I have to run XVMC to get 1080i de-interlaced.  For
almost a year I went without de-interlacing but several people have
improved this and it works very well.

 The only problems I currently have is when watching high-res and
seeking I get audio drop out when the OSD disapears.  .. That's it.  And
this is on a athlon 2600.  I very much do NOT recommend this setup and
if I had to do it over again I would go with a P4 3.2Ghz.  The reason is
I have several non-myth related issues that come up from time to time.
Doing backend and frontend on a single 2600 has some bandwidth problems.
When watching HD and recording 3 shows at once, and commercial detecting
is a lot for any system.  P4's hyper threading helps quite nicely with
keeping audio sound dropouts down when seeking.  My system locks at
times when stopping recording 3 shows and starting recording 3 new
shows, and when I'm watching a movie via mplayer, the movie stops for
2-8 seconds.  I also see much more video stuttering with mplayer.  The
fact is, HD is not a little thing.  I've had problems with data
throughput even with a 5 disk stripped raid system that moves about
100MB a second because recording 3 shows, commercial detecting one, and
watching another is simply too much for my motherboard's FSB to take,
period.  I also had more problems until I revamped which PCI/AGP cards
use which IRQ's.  

 My point I guess is, HD is right on the boarder of what current systems
can take, and in my personal experience it's not JUST cpu that matters,
it's your system bus.  They are not all created the same, and every
person doing HD will have things slightly different which can cause odd
problems.  My experience tells me that running an 800mhz FSB and a P4
3.2Ghz does a lot better for reducing chances of problems.  But then if
you're willing to take the time like I did, you can get something
working as I did.  

 The ideal setup is a 1-2Ghz backend holding the HD cards doing the
recording and a frontent only carrying about display and streaming
things over the network.  This setup would be very hard to have
bandwidth issues on either system.  

 I do believe HD in myth is ready, and has been.  Things are tweaked and
broken.  XVMC has more problems now with seeking than it used to, but
this is temporary.  Also, if you're running an older version you may
want to grab CVS and if you have a question if it's in a good state or
not e-mail me and I'll let you know.  Rarely am I more than a week past
CVS and I'll almost always find a bug if it's there.

 Oh, and BTW, here is the compiler settings I use.

-O3 -march=athlon-xp -m3dnow -mmmx -msse -mfpmath=sse

 And if you want about a 10% speedup, use gcc 3.4.  I did for some time
but I went back to 3.3 because I was trying to find out of 3.4 was
causing seeking issues, it wasn't, and I've been to busy to change
symlinks to 3.4 (mostly forgotten to).  3.4 should be fine and in fact
next build I'll be back to 3.4. 

Hope this gives some insight... Oh, I just remebered, last night seeking
did lock the frontend.  And a quick tip is even though you don't see the
text, hit the save possition button and it will save it, restart the
frontend and go... I saw this problem once in 5 hours of watching 50
shows (my weekly tv review session).  This is a known problem too, it's
just time to fix it, but it's so minor I overlook it. :)


On Sun, Oct 10, 2004 at 11:21:44PM -0700, Joe Barnhart wrote:
> --- Jarod Wilson <jcw at wilsonet.com> wrote:
> > So did you rebuild Myth against the down-graded ALSA
> > libs? I'm not 
> > certain it made a difference here or not, but I made
> > sure to do so on 
> > both systems that had problems and now don't.
> > Enabling extra audio 
> > buffering was the other key for me.
> I first went with 1.0.5rc1 with no change, then 1.0.5,
> also no change.  I can get 720p playback to work,
> sometimes, with Xv and "extra buffering" (and downhill
> with a tailwind).  XvMC never works at 720p, buffering
> or not.  The tables turn at 1080i, with Xv not able to
> keep up without sound gaps and stutters and XvMC able
> to play pretty well, except for the jaggies and
> freezing when the OSD comes up.
> As I recall you are using a modeline other than
> 1920x1080i, aren't you?  Are you doing the 540p thing
> like Doug?  I wonder if I'm taxing my system just a
> smidgen more, with hardware just a little less capable
> (Athlon 2800+, nForce2, 1G dual-channel memory,
> GF4MX).
> I guess I could pile on more hardware to make Xv work
> at 1080i without choking on the audio.  Its so darned
> wasteful, tho, having all this nice hardware assist
> and leaving it turned off!  I'd eventually like to
> have a system with three or four capture cards, so I
> want to use my cpu cycles sparingly.
> Do you think it would help to recompile everything
> (kernel, myth) for Athlon instead of 586 or 686?  (I
> doubt it, which is why I haven't done it yet.)
> On the other hand, I just want to get a stable working
> system, so maybe I'll trash the mobo and get an
> Athlon64 and let someone else worry about XvMC.  Don't
> take this wrong, but in a way I'm sorry you fixed your
> problem.  ;-)  It was nice having a lead blocker who
> is so well known in the Myth community.  As a
> newcomer, I don't expect to be taken as seriously.
> Joe Barnhart
> P.S. Here's another observation.  Setting chmod u+s on
> mythfrontend, XvMC uses about 55% cpu playing 1080i
> and has sound gaps every two seconds.  When I chmod
> u-s the cpu goes down to 37% and it plays without
> gaps.  Weird.
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