XvMC

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X-Video Motion Compensation, or XvMC, allows video programs to only send a graphics card differences from the last frame instead of sending a whole frame. XvMC can be used to reduce CPU utilization when playing back MPEG-2 video. In theory it should also reduce bus bandwidth requirements. Savings will be most dramatic with slow CPUs or when playing HD content. MythTV can be compiled to use XvMC for native playback. External players such as Xine and Mplayer can also be compiled to support XvMC. (Xine's plugin is oddly named xxmc.)


Software

Drivers

Unless otherwise noted, any mention of Nvidia hardware implies the use of the recommended Nvidia driver version for MythTV at the time of this writing: 1.0.7676

Supported Video Formats

Currently, only MPEG-2 is supported. This is usually a hardware limitation. As an exception, one of the Unichrome chips is capable of XvMC accelerated MPEG-4 playback, but the Unichrome driver doesn't support that functionality at the time of this writing.

Hardware

XvMC is currently supported in XOrg and thus MythTV on certain Nvidia and Unichrome video card hardware. Sadly, XvMC is not currently supported by the ATI drivers, even though the hardware is capable.

Example CPU Savings

  • A 2.93Ghz Celeron D w/1Gb DDR 3200 SDRAM with an Nvidia FX 5200 playing SD content uses between 8-12% CPU with XvMC enabled. Between 10-14% without.
  • (Add your example Hardware/Software/Content/CPU stats here)

Tips and Tricks

Prebuffering Pause or stutter with Nvidia

If you are using MythTV version 0.19 with an Nvidia card and experience these symptoms:

  • mild to moderate playback stutter
  • NVP: Prebuffering pause in your frontend log

Try disabling OpenGL VSync.

OSD Flicker

If you are using MythTV version 0.18 and you experience severe OSD stutter or flicker when XvMC is enabled, try upgrading to 0.19. The OSD flicker is fixed for the author in 0.19 with an Nvidia FX 5200.

Greyscale OSD

MythTV version 0.19 ships with a hack to enable full color OSD with XvMC enabled. However, the hack is disabled by default. To enable it, read this.

External Links