Comment on WAI-ARIA Role

I've trying to apply WAI ARIA to a video player done in HTML5 [1] and
ran into two questions:

- Are WAI ARIA user agents supposed to track all changes to aria
attributes?

 I have two examples:

 * aria-label:

  The volume button changes role  depending on its associated popup
slider. When the popup volume slider is visible, it enables the user to
mute or unmute the video. I update the label of the volume button
depending on the visibility of the volume slider.

 * aria-valuemax:

  I update the valuemax of the progressbar and the slider when receiving
a durationchange HTML event from the video (this happens at load time or
if the video is updated).

- I update some parts of the SVG, such as the logo of the play/pause,
depending on the state of the button itself. Since the ARIA functions
associated with the button are attached on a different element (ie the
mostly transparent rectangle in front), should I attach a presentation
role to the logos to ensure that the user agent will ignore those DOM
updates?


Thank you,

Philippe

[1] http://www.w3.org/2009/04/video-player.xhtml