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

[John Patrick Poet]

On Sat, 9 Oct 2004, Joe Barnhart wrote:

> I guess my expectations were too high.  I've been
> watching HD on my combo satellite/terrestrial receiver
> a couple of years now, and I expected Myth to be able
> to record and play signals equivalent to what I see on
> "normal" HDTV (terrestrial) broadcasts.  What I
> actually get on Myth is slow, jerky, stuttering
> playback that often hangs the frontend with something
> as simple as skipping forward or backward, or any
> activity that pops up the on-screen display.

<snip>

> Were my expectations too high?  Is this a matter of
> "rough edges" soon to be smoothed out?  Or is the
> current state of Myth unable to handle HDTV (at
> 1920x1080i) for anyone?  Should I dump my system and
> buy new Intel Pentium hardware?  Or just go back to
> the combo receiver and wait another year for the
> software to catch up?
>
> I would love to hear from anyone who is playing
> streams at 1920x1080i with no stutters or poor video
> quality.  What kind of system are you using?  Xv or
> XvMC?  Intel or AMD?  Video card?


I have been playing with Myth/HDTV since January.  It not was until March
that I had something usable.  My machine at the time:

2.6GHz HT P4 overclocked to ~2.8GHz
512MB DDR400 RAM
nVidia 440MX video card

Things I learned during this process:

1) NvAGP *must* be set right for your video card/motherboard.
   In my case, I needed to comment out/remove
      Option      "NvAGP" "1"
   from my xorg.conf file
2) Hyperthreading is a good thing.
   I built a kernel with Hyperthreading/SMP disabled which resulted in
   really bad stuttering.
3) Kernel 2.6.7 is a win.  Much better than any 2.4 kernel, both for
   recording and playback.  pcHDTV's 2.6.6 kernel patch works perfectly with
   the 2.6.7 kernel.
4) Building Myth/ffmpeg with optimizations for your processor is a win.
   For example:
       ./configure
       add/modify "-march=pentium4" in settings.pro and config.mak
       qmake
       make && make install
5) Recording, Watching and Commercial flagging could not all be done at the
   same time.  That system was just too slow.
6) Xv is better than XvMC -- if you have enough horsepower.


This all resulted in a machine which would play both 720p and 1080i material
pretty well.  It had consistent problems with close-up pans and scrolling
text, but it was watchable.

I decided that to fix the final issues, I must need to upgrade my CPU.  So I
relegated my 2.6GHz system to be my Myth backend, and for my front end, I
splurged on:

3.2GHz HT P4
512MB DDR400 RAM
nVidia FX5700LE video card

The result was a setup with almost exactly the same characteristics I had
before.  If there was any improvement, it was minor.  Obviously, the
extra CPU power was not as necessary as I thought.

Then Doug came along with his latest improvements to Myth.  He re-wrote the
audio/video synchronization code.  This made a small but noticeable
improvement.

Version 2 of Doug's synchronization code was the final piece.  Bruce got
involved and between them they fixed 99.99% of my stuttering problems.
Playback is now silky smooth.  I still get rare, very short, "micropauses",
but they are few and far between.

When ALSA 1.0.6a came out, I grabbed it and compiled Myth against it.  Major
problems.  Quickly went back and recompiled Myth against ALSA 1.0.5.

Hope this helps.


John