Beginning on March 9th, 2017, MPEG-DASH URLs (.mpd) will be removed from the payload of a Tweet that contains video. We will also stop serving requests these urls at the same time. MPEG-DASH support was an undocumented feature that we were experimenting with and ultimately decided not to move forward with.
As usual, you can reach us with any questions via the Media APIs category of the community forums.
Product Manager for Media Platform