I am not sure where to log this as a defect, maybe? But when using DXA 1.5 TBBs:
Generate dynamic component
Generate dynamic page
it recursively outputs json, which is really great, but it does not output an external url from a multimedia Component. Below Screenshot.
I can create an independent TBB to do so. Parse and get the MM Component, load it find the external url, and append the url to Json. But with keeping DXA and utilizing these TBBs out of the box, I would consider this would be expected functionality?