Use Closed Captioning

Closed Captioning allows live streams to have text versions of the audio rendered in-line to the video. This assists with foreign-language support, accessibility for the hearing impaired, and other scenarios.

Closed Captioning styles

The following are different styles of closed captions.

  • CEA-608 / EIA-608: This refers to the older style of closed captioning used by traditional analog television signals. They are inserted into the analog broadcast in line 21. These type of captions support limited languages such as English, Spanish, French, Portuguese, Italian, German, and Dutch. There is no formatting (captions are typically white all-caps text on a black background), and they are encoded in plain text.
  • CEA-708 / EIA-708: This refers to the newer, updated captioning style intended for use with digital television broadcasts. 708 captions support enhanced formatting (color, font, size, background) and additional languages through the use of Unicode character sets (for example, Japanese and Chinese). These captions are typically placed in the SEI NALU of h.264 video stream as picture user data.

Support for captioning

The onCaptionInfo() and onCuePoint() ActionScript callback methods in the incoming RTMP Stream are generally used to pass the 608 and 708 captions for HDS. These methods are implemented by an encoder internally and included in the RTMP stream. Check with your encoder vendor on the configuration options to enable captions. This captioning data will be passed through to the HDS output.

Note: Adobe's OSMF player and the Media Services Live’s HDCore plugin can recognize these methods. However, some programming must be done to toggle display of captions and, possibly, decrypt 708 captions from their binary data into a readable format.