SmoothStream track (format) label metadata is not made available

[rossbeazley]

This is a bug very similar to #1095

When parsing smooth streams, the label that can appear on StreamIndex is not propogated to associated Format objects. Inclusion of the label will make presenting choices of captions, subtitles or audio tracks nicer to the user.

This commit adds a failing test illustrating it and the fix is here.

Im currently trying to sort out access with our corporate CLA primary point of contact but its quite trivial and could just be transcribed if you wish. The PR is raised here.

[andrewlewis]

I'll take a look at submitting a simple fix directly and let you know if I run into any issues. Thanks!

[rossbeazley]

👌