The black turban thing is definately interesting... there must be a reason for it, nothing these guys seem to do is without some sort of symbolism.
Man detained for bomb threat at Buckley
By Rocky Mountain News
August 4, 2005
Security forces at Buckley Air Force Base are detaining a man who drove up to the base's Mississippi Gate at 7:45 a.m. and told guards he had two bombs in his vehicle.
Emergency and security personnel have isolated the vehicle for search. The Mississippi Gate is closed and all base traffic is advised to use the Sixth Avenue gate.
http://www.rockymountainnews.com/drmn/state/article/0,1299,DRMN_21_3977503,00.html
"there must be a reason for it, nothing these guys seem to do is without some sort of symbolism."
Assuming they use these tapes not just for rallying the masses but to send signals (not an unreasonable assumption), it is more likely they will use static visual cues rather than audio cues because they cannot control how al-Jazeera will edit the tape.
As long as a single frame of the video is aired, even if it is a still-shot, the signal is communicated.