I have been trying to edit an audio track in a new project. After dragging it into the timeline and pressing play I paused it and dragged the playhead back a few seconds. When I pressed play again it resumed from where I had paused it even though the playhead showed a few seconds behind. This kept happening even when splitting the track or rewinding back to the beginning. It is an .aac track is this not supported?
.aac does not support seeking. You should have received a warning dialog about this unless you previously chose to ignore warnings about unseekable or variable framerate video files. You need to convert this to a seekable format. You can either use a tool such as command-line ffmpeg to rewrap in mp4, mov, or mkv. Or, in Shotcut, after opening the file, use Properties > menu-button > Convert to Edit-friendly Format… and open the new file it creates when the job is done (double-click the completed job to open it).