This page provides two live web streams with subtitles to demonstrate the advantages of the combination of MPEG-DASH (Dynamic Adaptive Streaming over HTTP) with TTML (Timed Text Markup Language).
For more background information about the showcase see below.
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The stream shows content from the TV program of the public broadcaster Das Erste. The program was recorded and is played back in a loop but the encoding itself is done live.
Note: Due to changes in order to improve the streaming tests, this stream is currently not available here. Please use the external DASH.js player in the meantime!
This stream shows the regular TV program of the Bavarian Public Broadcaster Bayerischer Rundfunk (BR).
Note: At certain times of the day subtitles and/or the video may not be available. For legal reasons content may not be streamed or not be accessible everywhere. The broadcast content used as input may also have no subtitles. Alternatively please access the second stream ("ARD Live Service as recorded loop") which does not have regional constraints and has always subtitles.
TV subtitles have been an established service for decades, but in the Internet, subtitles for live streaming are still limited to proprietary solutions. MPEG-DASH (Dynamic Adaptive Streaming over HTTP) and the TTML profile EBU-TT-D (EBU Timed Text - Distribution) provide a standardised approach for live streamed subtitles. The demo streams are publicly available for anyone interested, specifically to demonstrate the potential of MPEG-DASH and EBU-TT-D to service providers and to the industry.
For the provided streams video and audio are encoded in different qualities and packed next to one subtitle track. The subtitle format used is EBU-TT-D. EBU-TT-D is based on the Timed Text Markup Language (TTML) and compatible with the TTML Profiles for Internet Media Subtitles and Captions 1.0 (IMSC1). Therefore the EBU-TT-D subtitle essence should be playable on any IMSC1-conformant presentation processor.
The streams use the DVB DASH profile which is mandated in HbbTV 2.0. The EBU-TT-D subtitles are packaged based on the relevant EBU-TT and ISOBMFF standards. As in a typical broadcast scenario the input for the BR Live Stream is the live broadcast signal in HD-SDI where the subtitles are embedded as teletext according to the standard SMPTE 2031.
In order to enable a smooth playback and proper display, the subtitles are chunked and delivered in a similar way to the audio and video content, encapsulated in MP4 segments.
Alternative access to the streams:
Akamai provides the CDN facilities and made necessary changes to support the live MPEG-DASH streaming service with subtitles.
BR (Bayerischer Rundfunk) is the content provider of the first, live program stream, integrated the Keepixo encoder in its operational streaming environment and provides both DASH streams.
Das Erste provided the content for the second, “semi-live” looped MPEG-DASH Stream which can be accessed worldwide without geo-blocking.
IRT coordinated the efforts and reviewed the sample streams.
Keepixo implements subtitle translation into EBU-TT-D, video transcoding into 6 profiles and MPEG-DASH packaging using its video encoding solution.
The implementation was supported by the EU funded project Hbb4All.
Contact: Andreas Tai, tai(at)irt.de