here is a review of such a Zep release:
1. The Devil's Blues (Genuine Masters, 1 DVDR-A), San Francisco 27 April 1969. A new concept of presenting audio was pioneered in 2004, on the sonically superior (and greater capacity) DVDR format, combining it with either still or moving images. Of the numerous releases the combined soundboard and audience recordings of the classic last night in San Francisco on 27 April 1969 has been chosen. The concert itself was superb, and the sound on this release is simply breathtaking, it could very well be an official release.
found here:
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www.undergroundweb.org.uk]