I stripped the audio track with -an when encoding for the web. The source has a
real mix at -19.2 dB mean / -3.1 dB peak, and the docs player is click-to-play,
so there is no reason for it to be silent. Re-encoded with AAC at 128k; levels
match the source exactly.
The other published films have no audio track at all to preserve — they were
rendered silent at source.