Synchronising broadcast and IP delivered components - IBC 2010
You get some interesting, and sometimes rather annoying, problems as soon as you have more than one device simultaneously presenting the same content or more than one delivery path for separate components of the same content. It gets even worse if you have two separate devices with two separate delivery paths.
Anyone with an AV amplifier hooked up to a TV receiver will have either struggled to get the lip-sync right or given up and stopped paying too much attention to lip movements. And if you like watching the Proms on TV whilst listening to the sound from Radio 3 then you will know that this is also an issue with digital TV, radio and streamed audio. Likewise the problem of having two radios tuned to the same radio station but via different platforms where the two radios present the audio at different times.
Of course not all content needs to be presented with such precise synchronisation as the main soundtrack. A director's commentary track is somewhat more forgiving and accompanying information like web pages and fact sheets just need to be available in the right segment of the programme. Work is progressing on several different approaches to synchronisation across BBC R&D, but here I will concentrate on our piece of work.
At IBC 2010 James Barrett and I showed his demonstration of a solution to the problem of getting correct lip sync where the main programme is delivered as a normal broadcast and an alternative soundtrack is delivered over an IP network. The demonstration proved that if the alternative audio can be made with accurate DVB timestamps that match those in the main service then, provided there is enough buffering in the receiver, the alternative soundtrack can be delivered to the television with the same accuracy as if it had been delivered as part of the broadcast stream. It is one possible way of increasing viewer choice without having to squeeze another soundtrack into our broadcast multiplexes.
You can read all the details in White Paper 185 : Enabling and Enriching Broadcast Services by Combining IP and Broadcast Delivery Mike Armstrong, James Barrett, Michael Evans which was originally published as our IBC 2010 Technical Paper.
Our demonstration was hosted by the EBU as part of The Broadcast Technology Futures group booth showing projects from the BBC, NHK and RAI under the banner Barrier Free Access. James Barrett also helped rig our stand and present our paper on the first day of the conference. The session was well attended and we had several questions from the floor and the paper generated a good flow of interested visitors to the stand to ask further questions. Roderick Hodgson joined us over the weekend and staffed the stand for the second half of the exhibition. We also had some very welcome assistance from Tony Churnside in between fulfilling his duties as the RTS Young Technologist of the Year.