Tvheadend

Tvheadend is still using the old, unofficial video/x-mpegts media type instead of the official video/MP2T media type⁰ for its MPEG TS streams, which can lead to problems with finding the default player for them.

$ curl -I http://localhost:9981/stream/service/6cc5c32919d098819c854a6a6c55049d
HTTP/1.1 200 OK
Server: HTS/tvheadend
Cache-Control: no-cache
Connection: Close
Content-Type: video/x-mpegts

VLC and other applications¹ have long since switched to using the official video/MP2T media type, and ffmpeg² and libav³ have been updated to use this as well.
(Yes, I know that this media type is supposed to cover only RTP streams, but most everybody is using it for HTTP and .ts files as well.)

As media type names are supposed to be case insensitive, I would suggest sending it in all lower case, video/mp2t, to prevent problems with buggy media type handlers and case-sensitive filesystems⁴.

[0]: http://tools.ietf.org/html/rfc3555
[1]: https://bugs.launchpad.net/ubuntu/+source/desktop-file-utils/+bug/552162
[2]: https://ffmpeg.org/pipermail/ffmpeg-cvslog/2014-May/077592.html
[3]: https://lists.libav.org/pipermail/libav-stable/2014-December/000912.html
[4]: http://lists.freedesktop.org/archives/xdg/2013-March/012711.html