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Closed Captioning

The Makito X supports capture, multiplexing and transport of Closed Captioning (CC) and other Line 21 information over Composite (with no 7.5 IRE setup on Line 21), as well as HD/SD-SDI input interfaces.

Closed Captioning data, as defined by the EIA-608-B standard, includes the following services over Line 21 Fields 1 and 2 of an NTSC analog video signal: CC1, CC2, CC3, CC4, Text1, Text2, Text3, Text4, and XDS (see following figure). The Makito X encoder supports transport of all these services. [Note that Closed Captioning as specified by EIA-608-B does not exist over PAL.]

Line 21 Services

Line 21 of each field can contain up to 2 bytes of information, which can be used by any of the above services (not simultaneously but rather successively). With NTSC video at 30fps, the maximum EIA-608-B mandated throughput represents:

2 bytes x 2 Fields x 30fps x 8 bit/byte = 960 bps

The block diagram below shows the workflow for video and CC data into the encoder.


Unicast and Multicast streams all carry the same CC data.

The Makito X encoder supports the capture of EIA-608 and EIA-708 closed captions from the HD/SD-SDI video input and transports it within the video elementary stream of the MPEG-2 Transport Stream.

The EIA-608 and EIA-708 captions are encapsulated in a Caption Description Packet (CDP), as described in SMPTE-334-2, within the VANC as mentioned in SMPTE 334-1. The Caption information is multiplexed and transported as per ATSC A/72 Part 1:2008 (ATSC A/53 Part 4:2007) in a CC SEI NAL. The CDP consists of a sequence of bytes that can hold the CEA-708 DTV caption data, CEA-608 caption data, caption service information, and SMPTE 12M-1 time code.

The CDP also includes the Caption Service Descriptor (CSD), as defined in ATSC A/65. The caption services stored in the CSD are announced in the MPEG-2 TS Program Map table (PMT).

With the support of EIA-708, ATSC A/72 mandates a dedicated link bitrate of 9600 bits/sec. (1200 bytes/sec or 20 bytes per frame for a p60 SDI signal). Of the 9600 bits/sec, 960 bits/sec are reserved for EIA-608 captions. 8640 bits/s are dedicated to 708-CC. This is a dedicated channel, so it has to be filled with filler data if no captioning information is present.

Supported resolutions include 1080p, 720p, 1080i, 480i, and 576i.

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