[b]Reaching a wider audience.[/b]
Reaching the blogosphere can provide a tremendous initial boost to your viewing figures. Boing-Boing is the most widely read blog. They like quirky electronics and video games (as demonstrated by Randy George) - if the video is also enjoyable it can trigger a chain reaction and make for a major success. This latter aspect is where I failed - my "faux theremin with walkie-talkies" video supplied plenty of quirk and not a lot of quality, so people were not inclined to look further. To compensate for that I added annotations (speech bubbles and clickable links,) but I did it too late to get the peak viewing period. The video has settled down on the sixth page of search results for [i]theremin[/i] by view-count.
[b]Reaching your target audience.[/b]
If you're searching youTube for [i]experimental theremin[/i] or [i]theremin music[/i] or [i]theremin music with effects[/i] then all your bases are belong to me! I totally dominate the search results for relevancy at the moment. The key here is honesty in advertising, and stating the obvious. All my Beat Frequency videos now have titles of the form "[song name] by Beat Frequency - experimental theremin music with effects."
[b]Reaching an international audience.[/b]
This started off as more "reaching your target audience." My target audience is (1) people interested in the theremin. (2) People interested in the sort of music I play. To address (2) I decided that a key phrase was "Throbbing Gristle" (For those who do not know, Throbbing Gristle were the band that introduced the term "industrial music" to the world in the 1970s, and they are cited as an influence on many of the myspace profiles of bands I like.) So I posted a little vlog (video-blog) giving my recollections of attending a TG gig as a promotional device to interest the Throbbing Gristle audience in my work. Results are still pending on that - it does not fit the bill for a running start via the blogosphere as my "faux theremin" video did. It's more of a slow burner.
But - getting to the point - someone posted a comment that it was hard to make out what I was saying. So I added subtitles. (A.K.A. Closed Captioning.) I used MovCaptioner. (http://www.synchrimedia.com/, US$25, 10 day free trial, Mac OS X only. Similar products are available for other platforms.)
This is what I have learned about youTube subtitles. Making them is easy, if a little time consuming. They affect youTube search results - I can search on text in the subtitles and find my video in the results. And... most importantly... youTube will auto-translate them into a fair number of other languages. So you can reach people who do not speak your language. And you can have multiple subtitle tracks. (Which could provide a reason for people to watch it more than once, boosting your viewing figures.)
So, how can this apply to your theremin video? For a "how to" video, either theremin construction or playing, a transcript of what you are saying is the obvious choice. A second subtitle track might contain additional details. For a music video you might use a subtitle track to talk about, for example, the history of the theremin, or how it works, or thereminists that have inspired you.
It's best to write with auto-translation in mind - use your spellchecker on everything; the translashun softwere canot handel rongly speld wurds lyk peeple kan. And use short sentences with common words with a single meaning. Also, avoid idoms, or the software might get a hitch in its giddy-up and translate it into something completely hatstand.
YouTube videos with closed captioning are not very common at the moment, so it's probably best to indicate their presence with an annotation at the start of the video.
Here is the youTube help p