Signaling Dolby Digital Plus bitstreams in an encrypted MPEG-DASH compliant ISO base media file

When Dolby Digital Plus bitstreams are included in an encrypted MPEG-DASH compliant ISO base media file, the header type value of the EC3SampleEntry box must be set to enca (a protected sample entry), indicating protection encapsulation as described in section 8.12 of ISO/IEC 14496-12. This prevents a playback client that is unable to decrypt the file from otherwise attempting to decode the Dolby Digital Plus audio data.

The EC3SpecificBox (which describes the configuration of the Dolby Digital Plus audio stream) must be immediately followed by a protection scheme information (sinf) box, which describes the type of encryption scheme, the initialization vector, and the key ID that must be used to decrypt the file. The sinf box must also contain an original format (frma) box, which describes the format of the original unencrypted track. The value of the frma box must be set to ec-3 for encrypted Dolby Digital Plus audio tracks.

The locations and hierarchy of the boxes that must be included in the stbl box to identify Dolby Digital Plus streams within an encrypted MPEG-DASH-compliant ISO base media file, together with the reference to the definition for each box, are listed in the table. The value of the nesting level provided for each box is based on the structure of the complete MPEG-DASH compliant ISO base media file.

Although the order of the EC3SpecificBox and sinf boxes is explicitly defined for Dolby Digital Plus bitstreams in the table, the order may not be the same for other encrypted video or audio tracks present in an MPEG-DASH-compliant file. Parsers must also be capable of processing MPEG-DASH files where the sinf box is the first box inside the enca box.