You could of course use an external still image and a silent audio clip.

But this feature will be really useful because if it is integrated in DoM you would know for sure that the frames are really black, and not potentially greyish because of bad color conversion or similair. It will also match the target container of the DCP.

For silent audio, integrated functionality would take care of matching the number of channels in the target DCP.

One way to implement this (at the end) is to allow negative trimming. But then the silent/black periods would not show in the timeline.

So in summary I think the best approach is to implement this as (black frames and/or silence) as some kind of "magic" source contents. This is the way some servers do it to insert black frames in a playlist without having a "real" ingested black DCP clip.

Thanks for considering!