You've got me curious, what is the item and power called?
you ask, i (eventually) answer:
mnemonic crystal (official dark sun 3.5): and now that i reread it, it is only effective with pages of material - basically a spy cam for text and/or spells. i now recall that the one in question i was thinking of was a homebrew variant that recorded minutes of video per level of crystal, with a flat rectangular field of view, instead of pages per level as normal.
mimir (official planescape 3.5): magic item that will record knowledge (spoken, possibly read) and regurgitate it... at length. only a cost given as they apparently can't be made, owing to setting fiat (made with an unknown material).
Sensory stones (official planescape 3.5): can record memories, sensations, and the like. no stats given due to setting fiat (only work inside one building in sigil, or somesuch). experience retrieval only.
Living Memory power (official planescape 3.5): can record almost any form of selected memory (whole or edited) into an object, which can then offer it back in text, visual, or direct experience formats.
Thought Bottle (Complete arcane): can store specific thoughts or memories (one day's worth).
and that's all that i'm thinking of off the top of my head. hope it was helpful. =D
PS: a creative use of illusion spells ought to do the trick as well, since you have the static illusion and the moving illusion options, if you are high enough level. combine with magic mouth for humorous additional commentary.