unable to rewrite metadata

[webfrog]

I'm not sure if this is a bug, but the path was writable and if the file format didn't support metadata how could it do it using the encode / rewrite metadata option ? It doesn't make any sense. It only works if I encode and rewrite but not just rewrite metadata?

-----error msg Unable to write metadata to output file. Either the path to the output file is not writable or this file format does not support metadata.