set isPlaying flag even if document is not playing

back 10 seconds

if application "VLC" is running then
	tell application "VLC"
		step backward
	end tell
end if
property step : 10
if application "QuickTime Player" is running then
	tell application "QuickTime Player"
		set playerPosition to (current time of front document) - step
		set movieDuration to duration of front document
		set isPlaying to (front document is playing)
		if (playerPosition ≥ movieDuration) then
			if front document is playing then
				stop front document
			end if
			set playerPosition to movieDuration
			set current time of front document to playerPosition
		else
			set current time of front document to playerPosition
			if (isPlaying) then
				play front document
			end if
		end if
	end tell
end if

forward 30 seconds

if application "VLC" is running then
	tell application "VLC"
		step forward
		step forward
		step forward
	end tell
end if
property step : 30
if application "QuickTime Player" is running then
	tell application "QuickTime Player"
		set playerPosition to (current time of front document) + step
		set movieDuration to duration of front document
		set isPlaying to (front document is playing)
		if (playerPosition ≥ movieDuration) then
			if front document is playing then
				stop front document
			end if
			set playerPosition to movieDuration
			set current time of front document to playerPosition
		else
			set current time of front document to playerPosition
			if (isPlaying) then
				play front document
			end if
		end if
	end tell
end if