Shouldn't this be:
0 (or -1) for all streams (default), n>0 (or > -1) for the nth stream.
I guess it is at least possible that the user knows in advance which
streams the source will offer.
It is very unlikely that this is known in advance. Also there is no reason
why you want to load more than a single variant at a time.
Note this are variants, not streams. Different variants bundle the same
streams with different resolutions.
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