Track "id" format?

I'm trying to implement the "id" attribute for in-band tracks<https://bugzilla.gnome.org/show_bug.cgi?id=711522>, and I'm wondering how IDs should be formatted.

For example, MPEG-TS's PID<https://en.wikipedia.org/wiki/MPEG_transport_stream#PID> is 13 bits, but I'm not sure if there's a standard non-binary way of representing it. Matroska / WebM have an arbitrary sized unsigned integer TrackUID<http://matroska.org/technical/specs/index.html#TrackUID>. Should we represent them as decimal, hexidecimal, or something else?

I assume we should use whatever formatting is common for each format, but I don't know what this is. Is there a good way to decide on this, or even better, an already-existing standard?