Many communities offer various shiurim and / or films during the afternoon. I don't know if this is available where you live, but in mine, shuls "compete" with each other.
During approx. the last decade, The Chofetz Chaim Heritage Foundation has presented 2 excelent videos on Tish'a B'av. Many shuls present one or both of them, and they are always excellent. I don't know, offhand, if they do a webcast, so check the web site or contact them.
Even if you don't find on of their lectures, Tish'a B'av is a great time to start learning Chafetz Chaim's book on Shmirat Halashon - laws of Lashon Hara. The Heritage Foundation as well as many Judaica Bookstaores sell his books in English translation, where you learn one law per day. If you've never learned it, I encourage a start. It will dramatically improve your behavior and outlook on life.