EEG encoders will automatically generate CEA-708 closed caption data when provided valid CEA-608 data. However, users can also enter CEA-708 data directly into one of the available Smart Encoder ports, in order for the encoder to insert that data into the video output.
Entering 708 Passthrough Mode
708 Passthrough mode can be entered via any Smart Encoder port on an EEG encoder, including iCap, Telnet, RS-232 serial, and modem. It uses the following format:
<Ctrl+C> corresponds to the hexadecimal value x03, while <Ctrl+A> corresponds to x01, and <CR>, or carriage-return, corresponds to x0D. arg1 is optional and can specify a 708 service, accepting values S1, S2, S3, S4, S5, and S6. If omitted, the command will use "S1" (service 1).
Entering Caption Data
Once you have entered 708 Passthrough mode, the data transmitted must consist of ASCII hex-encoded DTVCC packets, with commas separating the caption bytes and carriage returns delimiting the packets.
For example, the following sequence of ASCII characters would encode the 708 commands DeleteWindows, DefineWindow-0, and SetCurrentWindow-0, when terminated by a carriage return:
Including the trailing carriage return, this sequence corresponds to the following hexadecimal byte values:
38 36 2C 32 41 2C 38 43 2C 46 46 2C 39 38 2C 33 38 2C 33 43 2C 31 39 2C 30 32 2C 31 46 2C 32 39 2C 38 30 0D
Exiting 708 Passthrough Mode
As with other EEG Smart Encoder commands, <Ctrl+C> (corresponding to the hexadecimal value x03) can be used to exit 708 Passthrough mode.
Upconversion and Downcompatibility
When 708 Passthrough mode is active on a given service, upconversion into that service will be disabled. For example, if you caption to S1, CC1-to-S1 upconversion will be turned off while you are in 708 Passthrough mode on S1.
Additionally, 708 Passthrough mode does not allow users to encode CEA-608 downcompatibility bytes, which are required in many broadcast markets; many closed caption hardware and software products rely on CEA-608 data for proper operation.