Beginning on March 1st, 2016, WebM URLs will be removed from the payload of a Tweet that contains video. Twitter website, iOS, and Android applications no longer use WebM, and this video variant has very low consumption compared to other video formats. MP4 URLs will remain unchanged.
Approximately one week after removing WebM URLs from the Tweet payload, we will stop serving requests for all WebM videos.
Relative documentation and examples will be updated in advance of the update.
As usual, you can reach us with questions at @TwitterDev, or ask longer technical questions in the Media APIs category of the community forums.
Product Manager for Media Platform