It tells you that iMovie can't import files larger than two gigabytes in size and links a page that tells you how to split files into smaller chunks if you have QuickTime Pro. Here's an Applescript I wrote that will do the job for you automatically. Save it as a application with the Script Editor and drag your big movie files onto the application's icon. You'll be prompted for a folder for saving the resulting split movie chunks into. If you want to change the output folder, just open and save the application again using the script editor. This script also requires QuickTime Pro (5 or higher) and can take quite a long time to work if your dragged file is really big.

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property mydestination : choose folder with prompt ¬
"Choose a destination folder for the segments."

on open sourcefile
set this_time to 1
--set sourcefile to choose file with prompt ¬
"Choose a movie file you want split into segments."

tell application "QuickTime Player"
activate
stop every movie
try
if exists movie 1 then close movie 1

-- CHECK FOR THE CORRECT VERSION OF QUICKTIME
set the QT_version to (the QuickTime version as string)
set the player_version to (the version as string)
set the required_version to "5.0.2"
if (the QT_version is less than the required_version) or ¬
(the player_version is less than the required_version) then
set the error_message to ¬
"This script requires QuickTime " & ¬
the required_version & " or greater." & ¬
return & return & ¬
"Current QuickTime Version: " & QT_version & return & ¬
"Current QuickTime Player Version: " & player_version
my upgrade_QT(error_message)
end if

-- CHECK FOR QUICKTIME PRO
if QuickTime Pro installed is false then
set the error_message to "This script requires a
QuickTime Pro installation on this system."
my upgrade_QT(error_message)
end if

set myfile to open sourcefile

on error error_message number error_number
if the error_number is not -128 then
beep
display dialog error_message buttons {"Cancel"} default
button 1
end if
end try

--if not (exists movie 1) then error "No movies are open."

end tell
repeat
activate
display dialog ¬
"Enter the number of seconds for segments.
560 should make them less than 2 G in size." default answer ¬
"560" buttons {"Cancel", "Set Segment Length"} default button 2
copy the result as list to {segment_length_in_seconds, go_ahead}
try
if the segment_length_in_seconds is not "" then
set the segment_length_in_seconds to the ¬
segment_length_in_seconds as number
exit repeat
end if
end try
end repeat


repeat
try
tell application "QuickTime Player"

tell movie 1
set the selection end to (the selection start + ¬
(segment_length_in_seconds * time scale))
end tell
if (data size of movie 1) > 0 then
set start_name to name of movie 1
cut movie 1
make new movie
paste movie 1

set mynewfile to ((mydestination as string) & ¬
start_name & "_" & this_time)
with timeout of 3600 seconds
export movie 1 to file (mynewfile & ".dv") ¬
as DV stream using most recent settings
end timeout
close movie 1 without saving
else
error number -128
end if
end tell
set this_time to (this_time + 1)
on error
tell application "QuickTime Player"
activate
if (data size of movie 1) > 0 then
with timeout of 3600 seconds
export movie 1 to file (((mydestination as string) &
this_time) & ".dv") ¬
as DV stream using most recent settings
end timeout
close movie 1 without saving
else
close movie 1 without saving
end if
end tell
exit repeat
end try
end repeat
end open

on upgrade_QT(passed_message)
tell application "QuickTime Player"
activate
stop every movie
set the target_URL to "http://www.apple.com/quicktime/download/"
display dialog passed_message & return & return & ¬
"If this computer is currently connected to the Internet, " & ¬
"click the ?pgrade?button to visit the QuickTime Website."
buttons ¬
{"Upgrade", "Cancel"} default button 2
ignoring application responses
tell application "Finder"
open location target_URL
end tell
end ignoring
error number -128
end tell
end upgrade_QT

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