swf fisrt frame a start don't work !?

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Hello,
I test swf export, in Start movie options there are a check box for insert a frame a start Opaque or Transparent

I dont know who is the difference, just i have a black background, is it possible to insert correctly the first frame of the video whem the preload is OK, and the stop action at the first frame is actived?

Or is it possible to import a jpg? in the first frame??