The classic cross fade video transition gradually fades out the first video while fading in the second video creating a video cross-fade. This transition is typically used while creating slideshows.
The overlap intensity ranges from 0 to 100, which specifies when the transition should start fading out the second video while the fading in of the first video is in progress. At 100, the transition will start fading in the second video and fading out the first one at exactly the same time. At 0, the transition will fade out the first video completely to black and then it will start fading in the second video (no overlap).
By default this transition starts from the video in Video Track 1 and ends with the video in Video Track 2. Check this option to transition from Video Track 2 to Video Track 1.