[mythtv-users] What is HW XVMC MPEG DECODING

[Thomas M. Pluth]

XVMC stands for X Video Motion Compensation.  It's one of the two forms of
video acceleration that the Nvidia cards support, the other being IDCT
(Inverse Direct Cosine Transform).   These two features can offload some of
the graphics processing from your CPU to the GPU on your video card.  I
believe the Intel Extreme Graphics (845, 865 and 875 chipsets) also support
XvMC with the xorg driver (i830), but I haven't tried it.   

MythTV supports the use of XVMC on cards that support it, if Myth is
compiled with XvMC support and the correct libraries are linked in.   I've
played with it some, but unfortunately, the Nvidia drivers are not quite up
to the task of accelerating HDTV output just yet.  They don't support
interlaced output and scaling from one resolultion to another doesn't seem
to work quite right yet, either.  Another problem with using XvMC is that
the OSD in MythTV causes stuttering of the picture. 

It definitely helps offload processing for DVD resolution (720x480), and
with any luck Nvidia will get their drivers tweaked to work better at
1280x720p and/or 1920x1080i with the next release (whenever that is).

-----Original Message-----
From: mythtv-users-bounces at mythtv.org
[mailto:mythtv-users-bounces at mythtv.org] On Behalf Of Ryan Allen
Sent: Monday, June 21, 2004 2:33 PM
To: Discussion about mythtv
Subject: [mythtv-users] What is HW XVMC MPEG DECODING

In my previous posts, I fixed my no sound from TV and recordings problem
by disabling this.  When I installed knoppMyth last week, I choose the
"lx" option, which installed drivers for the LIRC and XVMC.  I searched
and scoured the Internet until I finally found a spec sheet for the
nForce chipset (gForce 4 on my motherboard) and it said it supported
"XVMC".  So I installed it.  However I still have no idea what it is.

Can somebody fill us in?  Thanks,

    -- Ryan