Interaction of checkpoints 1.1 and 1.3

The relationship between checkpoints 1.1 and 1.3 caused significant
confusion during last Tuesday's teleconference, and I am concerned that it
would be likewise obscure to most readers. This shortcoming could be
rectified by adding an explanatory note to checkpoint 1.3 which explains
that the combined effect of checkpoints 1.1 and 1.3 is that a description
of the video must be provided both as text, and as a synchronized audio
stream.

I would argue that such clarification is needed irrespective of the
proposed "Until most multimedia players [...]" qualification of checkpoint
1.3.