The tasks are arranged in the approximate order I am planning to tackle them.

+ - alpha code, please test and report any major problems
* - beta code, should be working, report any problems you find as bugs

Basic functionality
 + Open file
 + Open URL
 + Start
 + Stop
 + Pause
 + Quit
 + Full screen
 + Context menu
 + Shortcut keys
 + Main window title
 + Volume
 + Mute
 + Seek
 + Autosize
 + Status
 + Recent files
 + Maintain Aspect and Force Aspect options
 + Persist options between sessions
 + Maintain video size when docking states change
 + Enable and disable actions according to state

Additional controls
 + Zoom
 + Frame drop
 + Contrast
 + Brightness
 + Hue
 + Saturation
 + Popup sliders
   Tooltips when dragging a slider
   Display mplayer text output
   Audio delay
   Equalizer

Subtitles
 + Load from file
 + Load from URL
 + Autoload
 + Unload
   Delay
   Position
   Visibility
   Autoscale

Configuration dialog
   Tree like interface
   GUI-related options
   MPlayer executable path
   MPlayer additional options
   Video driver
   Cache size
   Filters
   Fine-tuning wizard

Drag and grop

Error handling

Playlist
   Path or URL
   Type
   Length
   Formats
   Bitrates
   Settings

Documentation

DVD support (when someone donates a DVD ;-)
 + Playback using dvd:// urls
   Menus
   Chapters
   Titles
   Choose audio language
   Choose subtitles by id or language
   Choose device
   Eject

Integration
   MIME file types
   KPart
   Widget

Mencoder support

Advanced options (may require patching mplayer)
   Video driver
   Audio driver
   DVD options
   VCD options
   CD options
   TV options
   Just about every option from mplayer(1)

Config file handling
   Read config
   Write config

Maybe
   Plugins
   Skins
