After trying some suggestions about turning off compositing, I finally discovered how to do it so it stays off.

Note this only works for Mythtv or for a desktop where you don't need or want compositing, and uses nvidia (as far as I know).

First, run Unity in 2D ⋯ this makes the Unity stuff overlaying the playback go away.

To do this, when you log on, press the gear like button on the login screen and select Unity 2D. If you bypass the startup login, you can log out and then to this when you log back in.

Second, turn off compositing in the xorg.conf file.

This is how:

Open a terminal and type in…

sudo nano -B /etc/X11/xorg.conf

The move the pointer to the end of the file and type in these three lines:

Section "Extensions"

    Option "Composite" "Disable"

EndSection

Ctrl-O and <enter> to save the changes, then Ctrl-X to close. Note that with the -B option, nano will save a backup copy as xorg.conf~

Then restart the X server or reboot.

If you are nervous about using the terminal to edit, you can use the text editor, gedit.

Open a terminal and type in gksu gedit. After putting in your password, you can edit system files, Be careful...!

Use the open command to open Filesystem: /etc/X11/xorg.conf and add the lines to the bottom of the file. Update: gedit does make a "~" appended backup file

Now, enjoy your Mythtv...!

If there is still tearing, one more thing you can do...

Edit your xorg.conf as above, this time adding a line at the end of the Section "Device"

Add this line:

    Option         "TripleBuffer" "1"

It now should look a lot like my HTPC xorg.conf file:

Section "ServerLayout"

    Identifier     "Layout0"

    Screen      0  "Screen0" 0 0

# commented out by update-manager, HAL is now used and auto-detects devices

# Keyboard settings are now read from /etc/default/console-setup

#    InputDevice    "Keyboard0" "CoreKeyboard"

# commented out by update-manager, HAL is now used and auto-detects devices

# Keyboard settings are now read from /etc/default/console-setup

#    InputDevice    "Mouse0" "CorePointer"

    Option         "Xinerama" "0"

EndSection



Section "Files"

    FontPath        "unix/:7100"

EndSection



# commented out by update-manager, HAL is now used and auto-detects devices

# Keyboard settings are now read from /etc/default/console-setup

#Section "InputDevice"

#    # generated from default

#    Identifier     "Mouse0"

#    Driver         "mouse"

#    Option         "Protocol" "auto"

#    Option         "Device" "/dev/psaux"

#    Option         "Emulate3Buttons" "no"

#    Option         "ZAxisMapping" "4 5"

#EndSection



# commented out by update-manager, HAL is now used and auto-detects devices

# Keyboard settings are now read from /etc/default/console-setup

#Section "InputDevice"

#    # generated from default

#    Identifier     "Keyboard0"

#    Driver         "kbd"

#EndSection



Section "Monitor"

    # HorizSync source: edid, VertRefresh source: edid

    Identifier     "Monitor0"

    VendorName     "Unknown"

    ModelName      "SAMSUNG"

    HorizSync       26.0 - 81.0

    VertRefresh     24.0 - 75.0

    Option         "DPMS"

EndSection



Section "Device"

    Identifier     "Device0"

    Driver         "nvidia"

    VendorName     "NVIDIA Corporation"

    BoardName      "GeForce GT 240"

    Option         "TripleBuffer" "1"

EndSection



Section "Screen"

    Identifier     "Screen0"

    Device         "Device0"

    Monitor        "Monitor0"

    DefaultDepth    24

    Option         "TwinView" "0"

    Option         "metamodes" "DFP: nvidia-auto-select +0+0"

    SubSection     "Display"

        Depth       24

    EndSubSection

EndSection



Section "Extensions"

    Option "Composite" "Disable"

EndSection

Good luck...!