HTTP Live Streaming playlist files with associated audio for receiver mixing

A single Dolby Digital Plus bitstream may include one or more associated audio programs in addition to the main audio program (program extensions).

For example, the associated audio program may be used to provide an audio description for the visually impaired or an audio presentation for the hearing impaired. The associated program is intended to be mixed with the main audio program after decoding. When providing content using these program extensions, we recommend providing the same content in all bandwidth variants.

If associated audio streaming is not always desired (for example, to provide different versions for different clients), we recommend that a rendition group that contains renditions with and without associated audio streams be made available. In a playlist, alternative renditions of the same content are identified with the #EXT-X-MEDIA parameter. To properly signal Dolby Digital Plus renditions using the #EXT-X-MEDIA parameter:

  • Provide a meaningful NAME attribute (for example, Movie for the rendition without an associated program or Movie with a spoken scene description for the visually impaired for a rendition with an associated program).

    Receivers may display the NAME attribute value for manual user selection and use the DDP-PROGRAM1, DDP-PROGRAM2, and DDP-PROGRAM3 attribute values to enable automatic selection of alternative content (for example, for visually impaired users).

  • For a rendition that contains associated programs, indicate the associated programs in the <attribute-list> of the #EXT-X-MEDIA parameter:
    • Add the DDP-PROGRAM0 attribute to the <attribute-list> of the #EXT-X-MEDIA parameter. The DDP-PROGRAM0 attribute must indicate the eight-bit substream information with an unquoted hexadecimal integer number as specified in this table.
      Table 1. Dolby Digital Plus PROGRAM0 bits
      Dolby Digital Plus PROGRAM0 bits Description
      b7 (most-significant bit) Reserved (must be set to 1)
      b6 Full_service_flag
      b5 to b3 Service_type
      b2 to b0 Number_of_channels

      The substream information for the DDP-PROGRAM0 attribute, listed in the table, is indicated in the same way as the comparable parameters of the E-AC-3 audio descriptor. (See the Semantics for the enhanced AC-3 descriptor section.)

    • If the Dolby Digital Plus stream contains an independent substream with a substreamid value of 1, add a DDP-PROGRAM1 attribute to the <attribute-list> of the #EXT-X-MEDIA parameter.
    • If the Dolby Digital Plus stream contains an independent substream with a substreamid value of 2, add a DDP-PROGRAM2 attribute to the <attribute-list> of the #EXT-X-MEDIA parameter.
    • If the Dolby Digital Plus stream contains an independent substream with a substreamid value of 3, DDP-PROGRAM3 attribute must be added to the <attribute-list> of the #EXT-X-MEDIA parameter.
    library_booksNote: We recommend also adding a DDP-PROGRAM0 attribute to the <attribute-list> of the #EXT-X-MEDIA parameter for the rendition that does not contain an associated program. The DDP-PROGRAM0 attribute describes the configuration of independent substream 0 (and, if present, any dependent substreams associated with independent substream 0) of the Dolby Digital Plus stream.
  • The DDP-PROGRAM1, DDP-PROGRAM2, and DDP-PROGRAM3 attributes must indicate the eight-bit substream information with an unquoted hexadecimal integer number as is also used in the E-AC-3 audio descriptor. (See Substream 1–3 field bit value assignments.)