Python DPX validator

Description
The tool validates the following set of header fields in a DPX file:


 * Magic number of 'SDPX' or 'XPDS' for reversed byte order.


 * A valid image data offset value.


 * Header format version number as 'V2.0'.


 * DPX file size in header matches what filesystem shows.


 * Encryption key is undefined and therefore image is unencrypted.

For more information about DPX, see the SMPTE standard ST 268-1:2014: File Format for Digital Moving-Picture Exchange (DPX).