SubStance - Live Subtitle Inserter

Over-the-top subtitling

Subtitles and captions are key to media accessibility as they let you reach a global audience. But accessibility regulations may vary between countries, making it difficult to design a global solution.

SubStance enables support for an infinity of subtitle profiles cost efficiently, ensuring synchronization between your content and the injected accessibility content. No content re-encoding, no CDN configurations modification, low-latency.

Simply feed SubStance with your contribution encoder output, or any standard DASH url, it will perform fMP4 muxing of TTML, generating standard compliant live DASH and HLS outputs that integrate seamlessly with popular CDNs.

Substance - live subtitle inserter

Tech Specs

  • Outputs: local file or push to a CDN using HTTP requests
  • Live edition of DASH manifest with minimal modifications
  • Synchronization toolbox
  • Runs on premise or in the cloud


ARD and RBB Text, two German broadcasters, wanted to add subtitles to their existing live streams to align accessibility between OTT and broadcast services.
These broadcasters wanted to anticipate expected regulations in this field. However they had a limited budget that prevented them from upgrading or replacing their existing encoders. They mandated Motion Spell to design a live subtitle inserter able to interface with their subtitles/captions generation tool and insert the result into existing OTT streams.
By making the process lightweight, with no transcoding and no CDN transfer involved, the solution checked all the boxes to make existing content workflows accessible to the widest possible audience.