The BBC have posted the 1968 video "Tolkien in Oxford" on their website at:
Most of the parts actually featuring Tolkien speaking have been excerpted before, so the linguistic content of the video is mostly well known already; but here is my transcription of the linguistic bits:
17:47 - "I first began seriously to invent languages about when I was 13 or 14. I've never stopped really. Languages have a flavor to me which I never understand people saying for instance, it's awfully dry or dull because a new language to me is just like getting a new wine or some new sweetmeat or something."
17:54 - Tolkien is shown writing a _tengwar_ inscription (Gildor's Quenya greeting, "_Elen síla_..."), comments on making a mistake in it, and recites the greeting.
18:58 - Regarding speaking Elvish, Tolkien says: "No. No. No. I wouldn't mind other people knowing it, and enjoying it, but I didn't really want to, like some people who have been equally inventive in languages [? desiring ?] to sort of make cults and have people speaking it all together, no, I don't desire to go and have an afternoon talking Elvish to chaps. For one thing of course Elvish is too complicated. I've never finished making it."
20:54 - Tolkien recites the Ring inscription. Notable here is his pronunciation of final _-g_ in _nazg_ as "guh", and of _-gh_ in _agh_ as "-kh".
21:18 - Speaking apparently of the Ring inscription and/or the Black Speech, Tolkien states: "I invented that in the bath, I remember. Yes, I remember inventing that in one of the baths, inventing it when I was having a bath, in 20 Northmoor Road. I still remember kicking the sponge out of the bath when I got [? the last and] all right that will do and jumped out." Tolkien lived at 20 Northmoor Road from 1930 to 1947.
Carl F. Hostetter Aelfwine@... http://www.elvish.org
ho bios brachys, he de techne makre.
Ars longa, vita brevis.
The lyf so short, the craft so long to lerne.
"I wish life was not so short," he thought. "Languages take such
a time, and so do all the things one wants to know about."