5.1 Channel Audio for the Streaming World
Colin Dixon, Broadband Media Practice Manager
June 15, 2009
Yesterday I paid a visit to Dolby in their beautiful downtown San Francisco building (it’s a converted train station and is really something to see.) I went to discuss Dolby Digital Plus and its impact on Internet Video. One of the problems with the previous incarnation, Dolby Digital, was that to get 5.1 channel sound you needed to dedicate nearly half a megabit/s. When a decent DVD quality movie is being streamed in as little as 1.5 mbps, having the sound add 33% to bandwidth requirements was a difficult proposition. Dolby Digital Plus does a much better job. It basically halves the bandwidth required for 5.1 sound to 224 kbps.
They also told me DD+ would work with Microsoft’s new adaptive codec called smooth streaming. Adaptive streaming technology works by the client signaling the streaming server when the broadband connection is degrading allowing the server to smoothly reduce the resolution of the video delivered. By doing this the show keeps playing no matter how bad conditions get on the broadband connection. If the audio doesn’t gracefully downgrade this is a huge problem, particularly if it’s using a half a megabit of bandwidth.
This is good news for the streaming world. Most streamed video services today do not support surround sound. But with Dolby Digital Plus in place hopefully that barrier will be removed in the very near future.
They also showed me the movie screening room on the third floor of the building. Of course, the sound is about as good as it can get there and can get pretty loud with a movie like, say, Transformers. It would surely disturb all the folks on the floor below. To fix this they suspended the whole screening from the ceiling! If it isn’t touching the floor beneath I guess there can’t be much noise transmission.
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