I have a mp4 file which has 3 audio tracks. When I open the file in ShotCut and drag it to the time line, I only get one of the audio tracks to the time line. On the preview window I hear all the audio tracks. How can I see all of the three tracks on the time line and mix them separately?
Add 3 audio tracks to the timeline, add the same clip to each of these audio tracks at the same time. Then, for each clip, select it and set Properties > Audio > Track as-needed.