[mythtv-users] MythTV experience with Intel Sandy Bridge graphics

[Keith Pyle]

There has been frequent discussion about the state of Intel graphics
and their Sandy Bridge chip capabilities, so I wanted to share our
recent experiences.  Here's the hardware and software being used for
the MythTV front-end system.

     CPU: Intel i5 2405S (2.5 GHz)
     MB: MSI Z68MA-ED55 (HDMI, DVI-D, VGA)
     Memory: 4 GB
     Drive: Intel SSD (caught a good! Black Friday sale)
     OS: Gentoo Linux x86_64 3.1.6
     Video drivers
         3D driver: mesa 7.11.2 (plus one patch)
         2D driver: xf86-video-intel 2.17.0-r3
         libdrm:    libdrm-2.4.29
     X: xserver-1.10.4-r1
     Compiler: gcc-4.5.3-r2
     Linker: binutils-2.21.1-r1
     C library: glibc-2.12.2
     
     MythTV Version   : v0.24.1-27-g30993d6
     MythTV Branch    : fixes/0.24
     Network Protocol : 63
     Library API      : 0.24.20110505-1
     QT Version       : 4.7.2
     
     Display: Samsung C8000 series plasma

Video and audio are over HDMI.  We're using the on-board Z68 graphics
(no add-in video card) and the classic mesa driver.

Myth experience: We started with the CPU++ standard playback profile
(ffmpeg & Xvideo).  There was a noticeable horizontal tear about half
way down the screen, most apparent during vertical panning of a
scene.  This wasn't surprising given prior reports of similar problems.

We tried switching to ffmpeg & opengl, but Myth would crash on starting
any playback.  A bit of debugging identified a null-pointer dereference
in the mesa video driver, which we reported to freedesktop.org.  They
fairly quickly posted a proposed (simple) patch which we have now
incorporated.  With the patch, playback works *very* well with ffmpeg
& opengl.  While I'm not a video engineer (nor do I play one on TV),
there are no apparent video defects and playback is completely smooth.
CPU load is up to ~25-30% on one core playing a 1080i HD recording from
the backend.  Audio quality is good as well.

We have not experimented with libva yet.

Power profile: At idle on the X desktop, the system pulls 31.2 watts, as
measured by a Kill-a-Watt meter.  With all 4 cores spinning at 100%, the
load is 66.1 watts.  Playing a video via mythfrontend draws 34.4.

Keith