* `encode()` raises an error when the command returns with non-zero exit status. We catch that in the higher-level conversion functions and skip to the next item without writing tags. * Simplified the handling of the `keep_new` flag.
Iincludes some more tests for the convert plugin. The test use the extended TestHelper class and the new pathlib (see #621).
When the conversion of an audio file fails during import the original should be imported. See #659
