Before you could just drop a .bik in the media folder, now it needs to be .webm. I used VLC media player (free to download) to convert my .bik startup to .webm, dropped it in the medias folder, worked like a charm.

How to convert:
Open VLC
Click 'Media' at top
Convert / Save (Ctrl R)
Choose Add - get video file (.mp4, existing .bik etc...)
Choose Convert
Change profile to Video - VP80 + Vorbis (Webm)
Create destination file named 'valve'
Drop file valve.webm into your Team Fortress 2 / tf / media folder
make sure -novid is REMOVED from launch options or NO startup video will play