Use movie_5.* instead of movie_300.* wherever possible

movie_5.* is faster to load, so is preferable where possible. All of the
tests already also use audio_5.*, which are even smaller, so this ought
not to expose any new problems. None of the test descriptions seem to
indicate that a big or slow-loading resource is required.
Merge pull request #721 from foolip/movie_300

Use movie_5.* instead of movie_300.* wherever possible