The following works for Quicktime Player X (10.1) in OS X 10.7 (Lion). It takes arguments from the command line and opens a movie, resizes it, sets the volume, and starts playing the movie (there are other properties you could add). Hopefully this is useful for someone like me who was trying to find examples of this, but only finding mounds of info for QuickTime Player 7 (and earlier), which doesn’t help much as many of the properties have changed.

-- AppleScript to open and control movie files in QuickTime Player X

-- The script is meant to run at the command line, like so:
-- $ osascript /path/to/movie.mp4 movie.mp4 800 60
-- If you don't want to use a shell, just remove this and 
-- the last line and manually populate the first 4 variables
on run argv
  set movieFile to item 1 of argv -- the full path with movie filename
  set movieName to item 2 of argv -- the file name only of the movie
  set desiredWidth to item 3 of argv -- the width of the movie on the screen
  set startOffset to item 4 of argv -- how many seconds into the movie to start
  -- this finds the right side of the screen, then offsets to the left
  -- the desired width of the movie
  tell application "Finder"
    set desktopBounds to bounds of window of desktop
  end tell
  set rightX to item 3 of desktopBounds
  set leftX to (rightX - desiredWidth)
  tell application "QuickTime Player"
    -- open the movie and bring it to the forefront (if other movies are open)
    open movieFile
    set lastOpenedWindow to (first window whose name contains movieName)
    set visible of lastOpenedWindow to true
    -- resize the movie using its original aspect ratio
    set movieBounds to bounds of lastOpenedWindow
    set widthOrigin to leftX
    set heightOrigin to 1
    set originalWidth to ((item 3 of movieBounds) - (item 1 of movieBounds))
    set originalHeight to ((item 4 of movieBounds) - (item 2 of movieBounds))
    set calculatedHeight to (round ((desiredWidth / originalWidth) * originalHeight) rounding down)
    set desiredWidth to (desiredWidth + widthOrigin)
    set calculatedHeight to (calculatedHeight + heightOrigin)
    set the bounds of lastOpenedWindow to {widthOrigin, heightOrigin, desiredWidth, calculatedHeight}
    -- if opening multiple movies, ensure they don't overlap
    set slideDown to 1
    repeat with aWindow in (get every window)
      set boundsOfAWindow to bounds of aWindow
      set heightOfAWindow to item 4 of boundsOfAWindow
      if (heightOfAWindow > slideDown) then
        if (name of aWindow does not contain movieName) then
          set slideDown to (heightOfAWindow + 1)
        end if
      end if
    end repeat
    set the bounds of lastOpenedWindow to {widthOrigin, (heightOrigin + slideDown), desiredWidth, (calculatedHeight + slideDown)}
    -- note, here we select a document, not a window
    set myMovie to document 1
    tell myMovie
      set audio volume to 0
      set current time to startOffset
      activate -- makes QuickTime Player the frontmost application
    end tell
  end tell
end run