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Using Switched Digital Video for the MPEG-4 Transition

A couple of savvy folks picked up on my near-throw-away reference earlier this month to the idea of using switched digital video as a tool for transitioning to MPEG-4. The basic concept is that operators could selectively broadcast MPEG-4 programming by offering it on a switched video tier. This would give them the ability to deliver higher-quality video and save bandwidth whenever MPEG-4 receivers (set-tops) were in use. The idea is tantalizing, but also much more complex than a two-sentence explanation suggests.

In digging through John Schlack’s technical paper on the subject, here are some of the details and clarifications I can offer.

The easiest way to make this work from a technical perspective would be to offer a premium service with additional MPEG-4 HD content. Subscribers to the service would get an MPEG-4 set-top and would be the only ones able to tune to switched channels with MPEG-4 programming. MPEG-2 set-top users simply wouldn’t see the channels as options.

Another way to deploy MPEG-4 content on a switched tier would be to implement forced tuning whenever an MPEG-2 subscriber requested a program being delivered with MPEG-4 encoding. With today’s equipment, this would require storing both an MPEG-2 and an MPEG-4 version of the program – not a problem when storage and streaming capacity are set up to be scaled separately. The system would deliver the MPEG-4 version when requested, and would force tune everyone to an MPEG-2 version if any MPEG-2 users requested the content. Force tuning has the potential to be somewhat disruptive, but there are solutions for mitigating that problem, like making sure both versions of a show are on the same QAM and/or waiting for a commercial break to force tune.

Theoretically, there should be no reason operators couldn’t also implement dynamic transcoding. In that instance, the switched digital video (SDV) system would dynamically transition between an MPEG-2 and an MPEG-4 stream, without the need to have two separate versions of a show queued. However, today’s decoders are not capable of dynamic transcoding, which means operators would have to spend money to deploy new decoders.

The end of John Schlack’s paper describes the benefits of using SDV for MPEG-4 delivery so succinctly that I’m going to quote it directly here. Any further questions? Drop me a line at marisilbey (at) comcast dot net.

Initially with a small number of MPEG‑4 capable settop boxes, SDV will be an enabling technology for deploying MPEG‑4 into the cable plant, allowing delivery of additional HD content and potential bandwidth savings. As the number of MPEG‑4 capable settop boxes grows beyond the deployed legacy settop box count, the cable plant will transition to broadcasting more MPEG‑4 content while delivering the MPEG‑2 content on the switched tier. This will provide further bandwidth savings.

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