Harmonize

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* Read source mtime only once as source may change during transcode

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* Fix double .. in file extension

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* Add opus support
* Make encoders configurable
* Refactor

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* Add `--quiet` flag
* Copy file mode
* Add __main__
* Misc cleanup

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* Stop chowning /source folder (Dominik)
* Use `.temp` extension for temporary filenames (Dominik)
* Log error when file already exists (Dominik)

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* Revert app import exposure