sampsyo/beets — pull request #246 by xhochy (2013-04-10 12:24:19+00:00)
Title: Compute Content-Length to make tracks seekable in most players via the web plugin

Flask only adds a Content-Length header if X-Sendfile is used. Media players like vlc (and Tomahawk which uses vlc as a backend) only enable seeking in a track if the Content-Length header is present.