Playing videos

I’m working on a project that involves the playing of .avi files from
a huge source library. Meta data about the files is stored in a
database and the files are stored elsewhere in a file structure that
is easy to access.

I’m new to video playback and what I have tried so far is
unsatisfactory. If I use send_file, the file downloads, opens a new
window and plays back. What the client is going to end up with is a
new window for each video.
I want to play the file back in the same window. I’m not really clear
how to proceed with do this, so if anybody can point me at any
resource (tutorial, book, whatever) that explains this I’d appreciate