The Descriptive Video Service (DVS), created by WGBH-TV in Boston [citation needed], is used by the Public Broadcasting Service (PBS) in the U.S. to provide video description for the visually impaired, so they can better understand what is happening on the video portion of the program. This greatly improves the experience and makes it much more valuable to blind and visually impaired viewers.
I've found that Fox also carries DVS on some of it's major programming and maybe movies too. One way to capture the DVS signal is to have an old VCR. (Made in the 80s) For some reason the old VCRs cannot recognize (and separate out) the DVS signal and it bleeds through the normal audio. I've accidentally taped some programs with the DVS, it's neeto. For Fox, i've found that that it tends to be the same announcer lady for multiple programs.
Maybe the next time the trilogy plays on tv, the DVS could be captured, it might be as easy as switching to SAP.
Here's an article about AotC's in Theater DVS:
http://ncam.wgbh.org/news/pr_05242002.html
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If you want to see if you can hear DVS audio, here's a site which lists upcoming programming with DVS:
http://www.tv-now.com/dvs/
Article about TPM on Fox which did have DVS: http://main.wgbh.org/wgbh/pages/mag/about/news/swepisodeone.html Also mentions that R2-D2 Under the Dome had DVS.