Splicing in SFN/MFN T2 networks

Insertion (splicing) in DVB-T2 SFN networks provides bitwise identity of the resulting streams at different segments of the SFN network. Such signals applied to synchronized transmitters allow the single frequency network to operate correctly. The bitwise identity is achieved by the initial conditions:

• Special processing of the original signal
• Media assets identity at all points of the SFN network
• Determinism of the insertion algorithm

Functionality and characteristics:

• During insertion of local ads using the splicing method into one or several selected multiplex programs MPEG TS (Transport Stream) is not parsed into components. Instead, fragments of MPEG ES (Elementary Stream) are replaced with an ES-stream composed of advertising content. This is done using a specialized algorithm that replaces up to four fragments of ES program with one T2-MI transport packet.
• Working at the level of elementary streams (both audio and video) provides full control over the filling of the VBV buffer (Video Buffering Verifier), the start and end points of ads insertion. This allows you to avoid problems during decoding ad insertion points on subscriber devices.
• Insertion process does not affect the components of the transport PLP (Physical Layer Pipe) streams along with CC (Continuity Counter), PCR (Program Clock Reference), and PMT (Program Association Table). The DVB-SI/PSI information (ISO/IEC 13818-1) also remains unchanged.
• An additional source of precision time signals is not required for this insertion algorithm.

• The diagram shows the workflow-algorithm of content replacing from PLP0 of the T2MI stream in "TV Service 3" program.
• The T2MI signal passes through the splicer without changes outside the replaced advertising blocks. Marks according to SCTE-35 and possible insertion points (IDR frames) are being searched. BB-frames being passed through at the T2-MI level as well as transport packets at the MPTS level are marked in grey.
• When replacing advertising content, the splicer replaces the packets of a specific program in MPTS at the transport layer with transport packets from spot-files, adjusting the PCR, taking into account the requirements of the Transport Stream Decoder Model (T-STD, according to ISO / IEC 13818-1), as well as models of video buffer control (VBV) and Hypothetical Reference Decoder (HRD, according to ISO/IEC 14496-10).
• In the diagram, replaceable transport packets in the video stream (Video PID) are marked in red, in the audio stream (Audio PID) - in green. The rest of the streams of the replaced program as well as other programs in this MPTS remain unchanged. Also, the data is re-encapsulated to the T2MI level, according to DVB Document A136. The BB-frames “recalculated” in this case are marked in yellow.

Advantages:

• The stream does not change and its structure is preserved - there is no risk of additional errors;
• There is no recoding - the quality of the original signal and media assets remains in its original form and does not deteriorate;
• It's possible to insert a large number of SD and HD programs simultaneously on one device;
• Because of recoding absence the delay of the TV signal does not exceed 120 ms;
• Software and hardware (relay) bypass modes initiated by the watchdog timer. The timer monitors all key nodes and device operation parameters. Bypass is automatically enabled and an SNMP alarm message is sent in case of deviation from the set values;
• There is possibility of seamless redundancy from the main and backup splicers due to the fact that streams are absolutely identical from the outputs of both devices;
• The correctness of elementary streams coming to the subscriber device even when the insertion is completed before the end of the ad block or the insertion is interrupted by the output label.

Inputs/Outputs:

• DVB-IP Multicast/Unicast UDP/RTP
• SRT
• DVB-ASI
• DVB-S/S2/T/T2/C/C2 (Input only)

Formats:

• DVB SPTS/MPTS/T2MI
• H.264 (ISO/IEC 14496-10)
• MPEG-2 (ISO 13818-2, ISO/IEC 13818-3)
• MPEG-1 audio (ISO 11172-3, Layer I and II)