Call recordings report does not handle recordings converted to mp3

I have a requirement to use mp3 for compatibility and size, but the call recordings module doesn't like this, and throws the following error:

Undefined index: mp3 File:/var/www/html/admin/modules/recording_report/Recording_report.class.php:234

and will not display any results. I don't see any reason why changing the format (and updating this in CDR) should have any impact on this, unless there's some record I am unaware of that needs updating.