Closed Captioning for Adaptive Bitrate Streaming

Integrate closed captions into streaming video content

Wowza Streaming Engine™ software integrates closed captioning into streaming video content, making online video accessible to a broader audience.

Make Your Video Streams More Widely Accessible and Include Captions in Multiple Languages

Make Your Video Streams More Widely Accessible

  • Include captions in multiple languages
  • Make content available to people with disabilities such as hearing loss
  • Comply with the United States FCC 21st Century Communication and Video Accessibility Act (CVAA) of 2010
Support for a Wide Array of Closed-Caption Formats for embedded captions in streamed video

Support for a Wide Array of Closed-Caption Formats

Just as there are a number of protocols, formats, and playback devices for streaming video, there are a number of types of closed-caption formats. Each adaptive bitrate streaming standard, whether HDS, HLS, or RMTP, supports different formats for embedded captions in streamed video. Wowza Streaming Engine provides the widest range of supported caption formats and caption-conversion capabilities of any media server for live and video on-demand (VOD) content.

Closed Captions for Live Streams

Inbound Video

For inbound live content, Wowza Streaming Engine accepts the following formats:

  • In-stream (embedded) CEA-608 captions (Line 21 captioning), the format used by traditional broadcast TV
  • AMF onTextData and AMF onCaption caption events in live streams

Through its Java API, Wowza Streaming Engine can also connect to back-end caption providers, allowing the server to ingest virtually any live caption format.

Outbound Video

For outbound video, Wowza Streaming Engine directly embeds CEA-608 or WebVTT captions in live streams played back via Apple HLS. For live events streamed via Adobe HDS or RTMP, Wowza Streaming Engine displays captions using onTextData events.

Closed Captions for VOD

For on-demand content, Wowza Streaming Engine can convert and deliver captions that are embedded in the video content as well as captions that are delivered in external files alongside the video content, sometimes called sidecar files. Wowza Streaming Engine can extract 3GPP Timed Text caption data from MP4 files or from companion files that use the following formats to specify caption data:

  • Timed Text Markup Language (TTML)
  • SubRip Text (SRT)
  • WebVTT
  • Scenarist Closed Caption (SCC)

This caption data can be injected into Apple HLS streams as CEA-608 or WebVTT captions or into Adobe HDS and RTMP streams as onTextData events.

Learn More about Closed Captions for VOD »

Supported Input and Output Formats

Caption Input Format Streaming Output Format
Apple HLS Adobe HDS RTMP
Live Embedded CEA-608 CEA-608, WebVTT onTextData onTextData
Embedded onTextData events CEA-608, WebVTT onTextData onTextData
Embedded onCaption event CEA-608, WebVTT onTextData onTextData
Other captions via API CEA-608, WebVTT onTextData onTextData
VOD Embedded 3GPP tracks (MP4 files) CEA-608, WebVTT onTextData onTextData
TTML files CEA-608, WebVTT onTextData onTextData
WebVTT files CEA-608, WebVTT onTextData onTextData
SRT files CEA-608, WebVTT onTextData onTextData
SCC files CEA-608, WebVTT onTextData onTextData
Embedded CEA-608 CEA-608