Nimble Streamer software media server supports WebVTT, SRT, TTML, CEA-608, CEA-708 and DVB closed captioning formats of subtitles for live and VOD output streams.
Closed captions for live streams
Several formats and scenarios are supported with live steaming subtitles. Closed captions can be delivered in NAL units of your content via any live streaming protocol supported by Nimble Streamer.
WebVTT via Automatic speech recognition
Nimble Streamer supports AI-powered speech recognition using various technology providers:
- Whisper library and model
- Speechmatics ASR service
- KWIKmotion AI powered captions service.
This feature set allows automatically generate closed captions and create translation subtitles for live streams. The output is provided as WebVTT subtitles for HLS live streams as well as for MPEG-DASH.
CEA-608 and CEA-708
These formats of subtitles are supported for MPEG-DASH and HLS as described in this CEA-608/708 article. If your input has those subtitles, your resulting streams will have them once you set it up.
SLDP protocol allows having both CEA-608 and CEA-708 as part of the stream after the same setup.
If your stream has that closed captioning and you want it to survive the transcoding, Nimble Live Transcoder supports subtitles passthrough for that purpose.
Convert between CEA-708 and WebVTT
If you need to generate WebVTT from CEA and vise versa, you can do that via Nimble on latest Ubuntu OSes.
DVB subtitles
DVB can be handled the following ways:
- DVB teletext can be converted into WebVTT.
- SDI DVB Teletext and Closed Captions can be captured from DeckLink SDI input.
- DVB Teletext can be forwarded via protocols and through Transcoder.
- Nimble Streamer can convert DVB subtitles into WebVTT for HLS live streams using image recognition AI.
- If your MPEG2TS or HLS stream has DVB subtitles, you can pass them through to output MPEG-TS and HLS.
- Live Transcoder can also pass DVB subtitles through so the resulting stream would have them.
So Nimble has full support for DVB for live protocols and for Decklink SDI.
Subtitles in DVR
Nimble DVR allows storing WebVTT subtitles alongside the video, using multiple tracks and exporting those subtitles into files.
Read this subtitles DVR capabilities description for more details.
Subtitles for VOD HLS and VOD DASH
Nimble supports the following subtitles formats for VOD:
- HLS: WebVTT, SRT and TTML
- MPEG-DASH: WebVTT and TTML
- Both include ABR support via SMIL files
Read this setup article to learn more about VOD subtitles support.
Playout subtitles
Nimble Playout (server playlist) allow inserting WebVTT subtitles alongside with respective VOD files input as part of its generated live stream.
You can also forward those WebVTT through Live Transcoder if needed.