I understand this feature has been requested previously https://forum.videolan.org/viewtopic.php?t=145140, but I don't feel that usage scenarios were adequately described and I would like to make another case for this feature to be added.
A Mixdown function would allow users to listen to multiple audio tracks at once, and to select multiple audio tracks in the menu bar interface. Please allow this configuration to be set as default in the Preferences, so that it can be rolled out as such in an enterprise setting. We would also appreciate a UI button to toggle the Mixdown functionality, and by default, sum all channels.
This feature is important to many different users of VLC player, including the broadcast industry which often uses the MXF file format with multiple tracks of audio. Our stations use the first audio track as the direct sound, and the second audio track as natural sound. Tracks 3 and 4 would be used for a stereo music track if that gets used in the package. I have also seen this feature request on the OBS website as that program is capable of outputting different audio devices on different channels.