ANSI SCTE 138-2019 pdf free download – Stream Conditioning For Switching Of Addressable Content In Digital Television Receivers
7. The PMT
SCTE 54 constrains each PMT PID to contain a single TS_program map_section.Any PMT structuresused by Addressable Content should conform to this constraint.[SCTE 54]
In systems where addressable content is present in the same transport stream as the Primary Channel, allof the PMTs shall be present in the transport stream at all times.Changes to any PMT in the vicinity of aFiller or Gap should be avoided.
Notes:
The preceding requirement will result in one or more PMTs being present in the transport stream that describe PIDs for which data will be present only when addressable content is present.
lt may be necessary to transmit PAT,CAT and PMT more frequently than required by SCTE54during the Filler in Level 0 Streams. The aggregate of PAT, PMT and CAT transmitted in thisinterval should not exceed 80,000 bits/second.
8.Level 0 Requirements
Level 0 Conditioning consists of a Filler, as defined in section 8.4, and video coding requirements definedin sections 8.8,8.9, and 8.10.The Conditioning described in this section shall be present in the transportstream at the input to a Client-DPI Device when a Level 0 Switch is enabled. In this context, “enabled”means that a Client-DPI Device may, as determined by its Decision Engine, perform a Level 0 Switch.The following requirements for Level 0 apply to both standard definition and high definition formats incoded video streams.
8.1. Use of Transport Streams and Services
In Level 0 systems, one or more transport streams may be used to convey the elementary streams
comprising an Addressable Content Set.All elementary streams selected as the result of a Level 0 Switchshall reside in the same transport stream and in the same service.
8.2. Video and Audio Elementary Stream Presentation Duration DifferencesDue to the fact that addressable content is preceded by Filler, a time difference(positive or negative) isintroduced between corresponding audio and video presentation time stamps(PTS). This difference isintroduced even when the original addressable content has been created with perfect synchronization.However, it can be shown (see Appendix B: Bound on A/V Presentation Time Mismatch Due to Splicing)
that under the following assumptions, the absolute value of the PTS difference introduced is bounded.Hence, the PTS differenice between audio and video introduced by any technique under the followingassumptions shall be less than or equal to one-half of the audio frame duration.
The presentation duration variance value calculations can be found in Appendix B: Bound on A/VPresentation Time Mismatch Due to Splicing. Those calculations shall be based on the following:
A/V Filler (black video, muted audio) is precomputed with a target duration(e.g.,0.5 sec)Ad is spliced in after Filler, and PTS values are restamped to be continuous with FillerVideo and audio frame periods are fixed and remain constant throughout Filler and adPES packets contain one video or audio access unit (AU)
The duration of the video Filler is calculated first. The duration of audio Filler is calculated tomatch the video Filler.
8.3. Conditioning of Primary Channel Streams
All of the video and audio elementary streams comprising the Primary Channel shall be Level 0conditioned, as defined in section 8.0 of this standard, when a Level 0 Switch is enabled.
8.4. Filler
Filler shall be present in all of the audio and video elementary streams which comprise an AddressableContent Set when a Level 0 Switch is enabled. Filler in video elementary streams shall consist of picturedata that will be decoded as black pictures. Filler in audio elementary streams shall consist of audio datathat will be decoded as silence.
Filler shall be comprised of compressed video and compressed audio matching the video and audiocodecs used to compress the Primary Channel and the addressable ads.
All Filler, Primary Channel and the addressable ad content shall not change PMTs during an InsertionSequence.
Picture format changes during an Insertion Sequence shall be restricted to changes in horizontalresolution and shall be compliant with either [SCTE43],[SCTE 128-1], or [SCTE215-1].
The transition from Filler to subsequent non-Filler content and non-Filler content to subsequent Filler inboth video and audio streams should not introduce any visible or audible artifacts.ANSI SCTE 138 pdf download.