The TrackSelection API returns two indexes, the index of the selected
track (`getSelectedIndex()`) and the index in the `TrackGroup`. The `HlsChunkSource`
and `HlsSampleStreamWrapper` should only work with the later.
Actually the `getSelectedIndex()`, current selected track index is really only useful on
the API to determine if there is a valid selection or not. The index is
really internal to `TrackSelection`
