There are two ways I know of in p.pro to fade audio or video. 1. yes using key frames, go to far left of track in timeline, click one of the small icons that pops up “show track….” and switch to show track/clip keyframe, click little key frame button and adjust from there. 2. go to effects(video or audio) select cross dissolve or dip to black for video and place it at fade point on clip, for audio select audio cross fade and place it at begginning or end of clip, adjust length of effect for desired length.