[mythtv-users] re: choppy HD playback

[Brandon Beattie]

Scott,

 I run an amd 2600+, I have problems running 1080i also.  It will run
fine if you turn of de-interlacing in the tv playback setup.  However,
the current algorithm for deinterlacing does not work well for high
resolution files (Such as HD).  At one point someone mentioned they were
going to write a couple new deinterlacing algorithms to help, but that
was a couple months ago.  In the future, your 2500+ /may/ be okay.  Most
of the problem with HD streams is not really myth, but the X server.  X
is very poor when trying to display HD.  (Not to mention it does not do
a good job at syncing frames and keeping video smooth).  When X is
re-written (as there is a project going on for this now) it will work
much better and will have true v-blank support.  You should be able to
watch 1080i on about a 1.7Ghz (This is what is required for windows that
properly handles v-blank and has a good de-interlacing for HD I've been 
told).  I personally recommend a P4 3.0Ghz with HT.  It almost doubles
your speed in regards to decoding HDTV and letting X suck up more
CPU cycles than it should really need.  The same stream on my 2600+ that
maxes out my CPU and is basically unwatchable, takes about 70% CPU usage
on a P4 3.2Ghz with HT.  Other possible issues are the way mythtv scales
video that is not native display size.  Right now, I (try to) transcode
all programs to 1024x576 (my native display size).  Transcoding is a bit
broken right now, but this takes care of things for me, but I don't
watch livetv, and this also saves disk space.  I also recommend a higher
CPU because if you want to transcode, the border line is not good.  Even
when watching transcoded shows, if the transcoder kicks in I can notice
it on my 2600+, the P4's with HT don't appear to be noticible.  I'm
waiting a bit to see if I can't find a dual P4 MB for cheap in a half
year and I'll pick up one of those for my mythbox.  Transcoder can use 1
processor, and my dvd, or livetv (If I do use it) can use the other.

That's my $.02

--Brandon

> Message: 3
> Date: Thu, 15 Apr 2004 10:19:21 -0500
> From: "Scott W. Edwards" <scott at swesound.com>
> Subject: [mythtv-users] re: choppy HD playback
> To: <mythtv-users at mythtv.org>
> Message-ID: <000101c422fd$074e51a0$0a05000a at ScottsVAIO>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Questions for the list: Is anybody running a Myth setup with the pcHDTV
> card and successfully playing back a HD (1920x1080i) stream? What CPU,
> ram , MB combo are you using? I have come to the conclusion that my
> Athlon XP 2500+ is not quite up the job of decoding the HD stream. It is
> OK for a SD stream. Here is my TOP while watching a HD channel:
> 
> top - 20:33:34 up 2 days, 9 min,  2 users,  load average: 4.36, 1.92,
> 0.74
> 
> Tasks: 100 total,   2 running,  98 sleeping,   0 stopped,   0 zombie
> 
> Cpu(s): 97.1% us,  2.6% sy,  0.0% ni,  0.0% id,  0.0% wa,  0.0% hi,
> 0.3% si
> 
> Mem:    514048k total,   510396k used,     3652k free,    16760k buffers
> 
> Swap:  1959920k total,        0k used,  1959920k free,   255240k cached
> 
>  
> 
> My hard drive is using dma, and I have tried compiling Myth with  XvMC
> support (hdtv patches applied) but this actually makes the problem
> worse.
> 
>  
> 
> I am considering 2 options: One is to drop in a Athlon XP3200+ with the
> 400Mhz FSB, or two, is to go with a P4 3.0Ghz. This would require a new
> MB and a complete rebuild of Gentoo and lots more money. Any advice
> would be appreciated.
> 
>  
> 
> Thanks,
> 
>  
> 
> Scott
>