Hi - in this particular case the problem is more on me than anything about Tumblr's API :) I know, celebrate the uniqueness of the situation ;)
What happened was when I first did Tumblr support for MarsEdit, it was clear the demand was strong for text editing, and the way that Tumblr supports audio and video in its API is a little different from everything else I support. So, I put it off, and it never ended up happening.
So MarsEdit doesn't support Tumblr video or audio posts, but it is still something I hope to add support for at some point. Sorry for the annoyance in the meantime.
Well, Tumblr is starting to be more annoying than its worth for anything other than ephemeral posts (i.e. a multimedia Twitter, or how I guess most people use Facebook) so I'm moving this particular project to Statamic.
Thanks for the reply!
ps - a little thing popped up that said "Click accept or reject beside an answer" but when I clicked Accept it said "You don't have permission to do that." FYI.
Whoah, funky! Thanks for letting me know about the forum nuisance. I've been really happy with Vanilla (current forums sw) compared with what I used to use, but frankly I'm looking forward to upgrading yet again to something like the hot new Discourse when it's ready for mainstream use.