Polistream OTT/WEB/VOD

Subtitles for live web streams are not easily supported by web-video players and the variable latencies in web delivery make synchronization difficult. If subtitles for live streams are required, they have usually been burnt-in as open subtitles prior to encoding as a web-stream. However, we’ve developed our own synchronization method to enable accurately timed subtitles to be delivered on live web-video feeds – as closed subtitles in one or more languages, without the need to encode multiple streams.

This innovative solution (a TVB Europe Best in Show award winner at IBC 2014), uses Polistream to add a time-stamp to the video as it’s encoded – then using code added to the player to analyze the timing data and display the correct subtitle (using the same image-based approach described above – except that the images are also created by Polistream). This technique has initially been successfully demonstrated using an Elemental HLS encoder with output to PC, Android and iOS – integration with encoders from other manufacturers is also under consideration.

A broadcaster’s Polistream system can now be easily upgraded to add an interface to their streaming video encoder so that real-time subtitling on any live broadcast is also conveyed on the simulcast web output. The same method can also be used with “live TV on the web” to deliver multi-language subtitles for pre-recorded programs.

This approach ensures reliable subtitles that are always in sync with the video regardless of the video player or platform – even when live video rewind or pause/resume is used.