When we began the item level encoding of the James Madison Carpenter Collection (multimedia folksong and lore) we were confronted with multiple tracks on each physical cylinder (translated to one digital file per cylinder). For better or worse we chose to use
<unitid type="start time">00:00</unitid> in the <did> for each track then
<p>Duration 00:00</p> in <scopecontent>
We were (and are) concerned with the ability to point to a location (start time) within a digital file, a desire we have not yet satisfied.
Robert Young Walser, PhD
The James Madison Carpenter Project