ANSI SCTE 19:2018 pdf free download – Methods for Isochronous Data Services Transport
5.3 Isochronous Data Bitstream Syntax
Isochronous data is carried as a Packetized Elementary Stream (PES). The PES payload, which follows the PES header specified by MPEG-2, begins with an isochronous data header, which is followed by isochronous data access units. The isochronous data header is present even when the PES header does not include a Presentation Time Stamp (PTS). Each isochronous data access unit is 16 bits (2 bytes; 1 word). Additionally, isochronous data access units are aligned with the PES syntax in that the first byte of the isochronous data header immediately follows the last byte of the PES header. Finally, isochronous data access units are aligned with transport packet payloads such that the first payload byte of an isochronous data transport packet is the first byte of an isochronous data access unit (following any adaptation, PES header, and isochronous data header fields), and the last byte of an isochronous data transport packet is the last byte of an isochronous data access unit. Stuffing bytes in the adaptation or PES header may be included to accomplish this. The syntax of isochronous data is as specified in the following paragraphs.
5.4.1 Reserved Fields reserved—Fields in this standard marked “reserved” are reserved for future use. Decoders shall disregard reserved fields for which no definition exists that is known to the unit. Fields marked “reserved” shall be set to a value of zero until such time as they are defined and supported.
5.4.2 Isochronous Data Sequence isochronous_data_access_unit—A 16 bit access unit of isochronous data where the first (left) bit is presented (output) before the second bit, etc.
5.4.3 Isochronous Data Header pts_ext8—An 8-bit field extending the PTS conveyed in the PES header of this PES as defined in ISO/IEC 13818-1. This field is the 8 most significant bits of the 9 bit Program Clock Reference (PCR) extension defined in ISO/IEC 13818- 1 that extends the time resolution of isochronous data PTSs from the MPEG-2 standard resolution of 11.1 µseconds (90 kHz) to 74 nanoseconds (13.5 MHz) for unambiguous determination of the correct access unit presentation time referenced by an isochronous data PTS. This unambiguous determination of presentation time supports each recovery without “bit slips”. data_rate_flag—A one bit flag which, when set to “1”, indicates that an increment field is present in the isochronous data header.
isochronous_data_header_length—A 4 bit field indicating the number of words (16 bits) of isochronous data header which follow this field including the reserved words, (units of 16 bits forces the isochronous data header to be an even number of bytes which, coupled with isochronous data access units, adaptation fields, and PES headers also being an even number of bytes, allows isochronous data transport packets to be generated without any padding bytes and thus higher efficiency) increment—A 28 bit unsigned even integer which indicates the isochronous data clock increment value and takes on values that describe the ratio of the isochronous data rate to a 27 MHz reference. Specifically