ANSI SCTE 35-2019 pdf free download – Digital Program Insertion Cueing Message for Cable.
6. Introduction
6.1. Splice points (Informative)
To enable the splicing of compressed bit streams, this standard defines Splice Points. Splice Points in an MPEG-2 transport stream provide opportunities to switch elementary streams from one source to another.
They indicate a place to switch or a place in the bit stream where a switch can be made. Splicing at such splice points may or may not result in good visual and audio quality. That is determined by the performance of the splicing device. The use of “advanced” video compression, such as documented by ITU-T H.264/ ISO/IEC 14496-10 (“AVC”) or ITU-T H.265/ ISO/IEC 23008-2(“HEVC”) typically requires advance notice of Splice Points to permit the video encoder to create a spliceable point in the video elementary stream. In most systems this is provided by the use of [SCTE 104] to provide a communications path from the programmer’s Automation System to their Compression System. These AVC and HEVC coding constraints for splice points are documented in [SCTE 172]. Transport streams are created by multiplexing PID streams.
In this standard, two types of Splice Points for PID streams are defined: Out Points and In Points. In Points are places in the bit streams where it is acceptable to enter, from a splicing standpoint. Out Points are places where it is acceptable to exit the bit stream. The grouping of In Points of individual PID streams into Program In Points in order to enable the switching of entire programs (video with audio) is defined. Program Out Points for exiting a program are also defined. Out Points and In Points are imaginary points in the bit stream located between two elementary stream presentation units. Out Points and In Points are not necessarily transport packet aligned and are not necessarily PES packet aligned.An Out Point and an In Point may be co-located; that is, a single
presentation unit boundary may serve as both a safe place to leave a bit stream and a safe place to enter it.The output of a simple switching operation will contain access unit data from one stream up until its OutPoint followed by data from another stream starting with the first access unit following an In Point. Morecomplex splicing operations may exist whereby data prior to an Out Point or data after an In Point aremodified by a splicing device. Splicing devices may also insert data between one stream ‘s Out Point andthe other stream’s ln Point. The behavior of splicing devices will not be specified or constrained in anyway by this standard.
6.2. Program splice points (Informative)
Program In Points and Program Out Points are sets of PID stream In Points or Out Points that correspondin presentation time.
Although Splice Points in a Program Splice Point correspond in presentation time, they do not usuallyappear near each other in the transport stream. Because compressed video takes much longer to decodethan audio, the audio Splice Points may lag the video Splice Points by as much as hundreds of
milliseconds and by an amount that can vary during a program.
This standard defines two ways of signaling which splice points within a program are to be spliced.Aprogram_splice_flag, when true, denotes that the Program Splice Mode is active and that all PIDs of aprogram may be spliced (the splice information table PID is an exception; splicing or passage of thesemessages is beyond the scope of this standard).A program_splice_flag,when false, indicates that theComponent Splice Mode is active and that the message will specify unambiguously which PIDs are to bespliced and may give a unique splice time for each. This is required to direct the splicing device to spliceor not to splice various unspecified data types as well as video and audio.
While this standard allows for a unique splice time to be given for each component of a program, it isexpected that most Component Splice Mode messages will utilize one splice time (a default splice time)for all components as described in section 9.The facility for optionally specifying a separate splice timefor each component is intended to be used when one or more components differ significantly in their startor stop time relative to other components within the same message.An example would be a downloadedapplet that must arrive at a set-top box several seconds prior to an advertisement.
6.3. Splice events (lnformative)
This standard provides a method for in-band signaling of splice events using splice commands to downstream splicing equipment.Signaling a splice event identifies which Splice Point within a stream touse for a splice. A splicing device may choose to act or not act upon a signaled event (a signaled eventshould be interpreted as an opportunity to splice;not a command). A splice information table carries thenotice of splice event opportunities.Each signaled splice event is analogous to an analog cue tone.Thesplice information table incorporates the functionality of cue tones and extends it to enable the schedulingof splice events in advance.
This standard establishes that the splice information table is carried on a per-program basis in one or morePID stream(s) with a designated stream_type. The program ‘s splice information PID(s) are designated inthe program’s Program Map Table(PMT). In this way, the splice information table is switched with theprogram as it goes through remultiplexing operations. A common stream_type identifics all PID streamsthat carry splice information tables.Remultiplexers or splicers may use this stream_type field to dropsplice information prior to sending the transport stream to the end-user device.ANSI SCTE 35 pdf download.