Codec type indication for Dolby AC-4

The codec type must be indicated in an HLS playlist.

For media streams containing Dolby AC-4, we recommend using the CODEC attribute of the EXT-X-STREAM-INF parameter to indicate the codec type. The CODEC must include a dot-separated four-part value for media presentations using Dolby AC-4, as shown in this example:

#EXT-X-STREAM-INF:BANDWIDTH=3464568,CODECS="avc1.640028,ac-4.02.01.01"
example.m3u8

The FourCC ac-4 part indicates that the codec is Dolby AC-4. The latter three parts are represented by two-digital hexadecimal numbers and indicate these parameters sequentially:

  • The bistream_version as indicated in the ac4_toc(), which is defined in ETSI TS 103 190-2
  • The presentation_version as indicated for the presentation in the ac4_toc(), which is defined in ETSI TS 103 190-2
  • The mdcompat parameter as indicated for the presentation in the ac4_toc(), which is defined in ETSI TS 103 190-2

An object type indicator (OTI) value must not be appended to the ac-4 string.[1]

[1] The object type indicator value is not defined for Dolby AC-4.