[mythtv-users] HDTV on Myth -- not a "myth" CONCLUSION

[Joe Barnhart]

First off, I want to thank everyone who shared
information and enlightened me on this topic.  As
always, I have learned a tremendous amount from the
keep knowledge well of this list.

Here are some facts I have learned:

1. Xv is more tested and debugged than XvMC. It has
been stable for much longer and is preferred for its
flexibility (e.g. filters) and its integration with
the video architecture of Myth.

2. Xv has higher computational load than XvMC.  A
marginal processor won't cut it.  The hyperthreading
of the P4 is an advantage, but it isn't clear yet how
much.  I know my Athlon 2500+ is not up to the task of
decoding 1080i material on Xv.

3. The video card makes a tangible difference.  I
tried an nVidia 5200 card as a drop-in replacement for
my GF4MX card, and I was able to smoothly decode 1080i
on Xv, but only while there was no commercial flagging
going on in the background.  One other difference in
the card was AGP 8x in the 5200 vs. 4x for the GE4MX.
Neither card chose to use fast writes, however.

4. Factors other than raw processor speed can affect
the system performance.  For example, the PCI
backplane can get "swamped" even though the processor
is at less than 100%.  This can happen due to HDTV
streams being recorded from one or more cards while
being played back from the disk. HDIV performace is a
system issue, not any individual component.

5. Consider separating FE and BE processes to
eliminate tasks from affecting one another.  Take my
example of commercial flagging for instance.  Move it
to a separate machine and it won't interfere with
playback on Xv.

6. Don't use alsa 1.0.6 drivers, they have been
implicated in video jerkiness.  Do enable "extra audio
buffering."  Do use gcc 3.4 instead of 3.5 for
slightly better performance (what about earlier
releases? I'm on gcc 3.3)

7. If stability is of highest importance, match the
hardware and software used by the developers of HDTV
on Myth.  Use the Pentium 4, enable HT, and choose Xv
on an nVidia card.  If you want to contribute and help
debug new platforms, choose something else. ;-)

I hope this adequately summarizes what I've learned in
the last couple of days.  I'm limping along with my
Athlon 2500 and GeForce 5200 card right now, but
planning to replace the mobo with a more capable one
and dedicate this one to a BE server with lots and
lots of HD-3000 cards and stacks of cheap Fry's hard
disks (I wish).

Joe Barnhart




		
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