[mythtv-users] HD, the holy grail...

[Shawn Rutledge]

I wrote a few months ago about problems getting adequate myth HD
performance.  I'm taking a break from myth with HD at least because
the conclusion then was that it seemed hopeless without upgrading to a
dual core processor (currently Athlon XP 2400+).  I have a correct
channels.conf, I think.  It's not taking excessive CPU when I run it
like this:

/usr/X11R6/bin/xinit /usr/bin/xine --video-driver xvmc -D -g -f dvb://]

I will get to some less important questions below but the big one is I
why I'm getting dropped frames.  I see the usual digital corrupt-MPEG
type artifacts (big blocks with incorrect colors interspersed through
the frame, and some frames gone completely).  It's clearly not CPU
limited now (where with myth, there was a possibility that was the
problem).  I tried azap to measure signal strength:

[muon][01:38:30 PM] azap "KNXV HDTV"
using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
tuning to 725028615 Hz
video pid 0x0031, audio pid 0x0034
status 00 | signal 0000 | snr 0000 | ber 00000000 | unc 00000000 |
status 1f | signal 0000 | snr ff91 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 0000 | snr ffd9 | ber 00000000 | unc 0000003d | FE_HAS_LOCK

uh... signal strength zero and SNR so high?  I guess I will assume the
HD-5500 driver doesn't report signal strength correctly.  SNR being so
high leaves me disinclined to blame the antenna.  I'm using what I
think was a VHF optimized yagi (bought it years ago at RadioShack when
I was trying to get better FM reception out in the boonies), and
that's a UHF station I think, but OTOH I'm not so far from the
transmitter now so any old antenna would probably pick it up.

More unanswered questions would be why I need that last bracket,
dvb://] - it was a random typo but it doesn't work if I leave it off;
and why xine can mostly work on this machine but myth requires so much
more horsepower.  Top output looks like this

top - 13:45:24 up 3 days, 13:34,  2 users,  load average: 0.40, 0.11, 0.07
Tasks:  62 total,   2 running,  60 sleeping,   0 stopped,   0 zombie
Cpu(s): 32.7% us,  2.0% sy,  0.0% ni, 64.3% id,  0.0% wa,  0.3% hi,  0.7% si
Mem:    515828k total,   509664k used,     6164k free,    11392k buffers
Swap:  1959920k total,      236k used,  1959684k free,   309708k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
18057 root      15   0  206m  24m 7120 S 32.9  4.9   0:10.98 xine
18079 root      10  -5     0    0    0 S  1.0  0.0   0:00.31 cx88[0] dvb
 2507 root      10  -5     0    0    0 S  0.3  0.0   1:01.92 msp34xx

so xine can decode with only 32% CPU, but myth seems to require much,
much more.  Even if I leave off the --video-driver xvmc from xine, it
goes up (40-something for xine and 20-something for X) but total CPU
is still less than 100%.

I'm also getting crappy audio with my old WinTV board which I try to
use with Myth for cable, but that's a problem for another day.  Oh,
and the C key does not work right now (why!?! it did last time I was
trying this, a few months ago...) to switch inputs so I can't actually
get to that card right now, so myth isn't doing anything useful at the
moment except showing snow.  It will not switch channels on the 5500
and it can't switch to the WinTV board at all.  xine can switch HD
channels just fine, though.

Anyway I'd try to put up with plain old xine for a while if I can just
solve the dropped frames problem.  My wife only wants to see two
things on TV - ER, and the Oscars.  The Oscars are tonight.  Both can
be received in HD here.  We should be getting plenty of signal
strength.  Is it so much to ask?  I do not have time for Myth to be my
full-time hobby so I still use a VCR to record ER because Myth has
never worked well enough.  Last time I managed to actually record
something it had the crappy audio problem.

At least I'm not having to scale down to 640x480 anymore; I got a
Panasonic AX100 projector and love it.  1280x720, 2000 lumens.  Mostly
we're still having to use the composite input though because of
computer problems.  Guess I could just get a mac mini and run Front
Row on it, right?

Some day I will get a dual-core machine and try again to get myth to
handle HD.  Some day, when everyone else is already using readily
available HD decoder boxes that cost next to nothing...