The default filename for a master download has been changed from master.mp4/m4a to mezzanine.mp4/m4a.
These files are also now served from mezzanine.mux.com, which replaces master.mux.com.
If your system is dependent on the "master" filename or hostname, contact support to keep the legacy filename and hostname.
The filename of a downloaded file can also be customized by using the download query parameter.