I'm not sure how to deal with WCAG 2.0's success criterion 1.2.5. It says:
Audio description is provided for all prerecorded video content in synchronized media
Do I have to provide an audio description for a silent video, showing how to build a paper plane to meet AA? The definition of synchronized media unfortunately doesn't appear to be very helpful.
In your case 1.2.1 is relevant, not 1.2.5, because you have a video without sound. See "video-only":
a time-based presentation that contains only video (no audio and no interaction)
1.2.1 Audio-only and Video-only (Prerecorded) says:
For prerecorded audio-only and prerecorded video-only media, the following are true, except when the audio or video is a media alternative for text and is clearly labeled as such: (Level A)
- […]
- Prerecorded Video-only: Either an alternative for time-based media or an audio track is provided that presents equivalent information for prerecorded video-only content.
So you'd have to provide an alternative to the video, like a text explaining how to build a paper plane or a spoken record of that explanation.
/edit: Ah, sorry, I read over that you want to get AA. So yeah, as far as I understand you'd have to offer an audio track for the video-only.
I think it would be helpful to explicitly state that there is no audio at all, too. But this is not a requirement afair.