In a sequence having three video files lined up (synced), I did the usual Razor Cut up front to clear away garbage, but lo and behold, some symbols popped up on the cut line and at the beginning on video 2. The symbol is a white box outlined in bright red, with the left edge thicker and shaped something like a [ bracket.
Inside the symbols, the two Video line symbols have a -1 in them, and the Audio line symbols have a +1.
I can't figure out what to search for in the Help, so does anyone know what about them?
It means your video and audio are out of sync by one frame. In addition to cutting, you must have accidentally moved one of the clips.
Those symbols mean that video and audio portions of a clip have become unsynced. The numbers indicate how many frames out of sync the clip portions are. Check out the bottom of this help file entry for information on how to fix it.