NALs with CEA608 captions go in. Cues come out.
Lead Maintainers:
- Jon-Carlos Rivera @imbcmdth
- Joe Forbes @forbesjo
- Matthew Neil @mjneil
- Oshin Karamian @OshinKaramian
- Garrett Singer @gesinger
- Chuck Wilson @squarebracket
Maintenance Status: Beta
CaptionStream is the main class here, and you'll want to use it pretty
much like a standard node.js stream, but with two optional arguments in
the constructor:
// if not provided, timescale is 90000 and CueObject is a simple wrapper
var captionStream = new CaptionStream(timescale, CueObject);Register to the data event to receive caption objects of type
CueObject, whose interface must conform to the VTTCue interface, but
can be any object.
Push NALs with CEA608 captions into the CaptionStream with
CaptionStream.push. When you think it's appropriate to flush,
call CaptionStream.flush.
When new streams are detected, a newStream event is dispatched with the
stream as the data of the event (e.g. CC1, CC2, etc).
If you're using this project in a node-like environment, just
require() whatever you need. If you'd like to package up a
distribution to include separately, run npm run build. See the
package.json for other handy scripts if you're thinking about
contributing.
Captions come in two varieties, based on their relationship to the
video. Typically on the web, captions are delivered as a separate file
and associated with a video through the <track> element. This type
of captions are sometimes referred to as out-of-band. The
alternative method involves embedding the caption data directly into
the video content and is sometimes called in-band captions. In-band
captions exist in many videos today that were originally encoded for
broadcast and they are also a standard method used to provide captions
for live events.
In-band HLS captions follow the CEA-708 standard.
- Rec. ITU-T H.264: H.264 video data specification. CEA-708 captions are encapsulated in supplemental enhancement information (SEI) network abstraction layer (NAL) units within the video stream.
- ANSI/SCTE 128-1: the binary encapsulation of caption data within an SEI user_data_registered_itu_t_t35 payload.
- CEA-708-E: describes the framing and interpretation of caption data reassembled out of the picture user data blobs.
- CEA-608-E: specifies the hex to character mapping for extended language characters.