Looks pretty awesome. Minor nit: hitting backspace to delete a clip (pretty common in editing apps) forces the browser to go back. You might also want to catch other types 'leave page' events and ask for confirmation so that the user doesn't lose their work accidentally.
Also, trim music gave an error for me too. Do you have a place to drop bug reports?
Hasnt effected paying users yet, so it's lower priority, but will be addressed soon.
I am thinking about improving that UX. Instead of immediately prompting the user to trim. This will be in the toolbar as a "tool". So if you want to trim a podcast episode you can, that is the main use case, so it might make the most sense this way.
I slapped this in quickly because I was targeted podcasters for the first few customers and this was a critical tool to have.