Back when US broadcasters first received their digital channel assignments for HDTV, they began to dream up additional services which could be launched on top of the live HDTV service.
It’s been a long time coming, but a commercially viable contender for the first of these was announced yesterday by Fischer Communications and Hubbard Media who introduced MyDTV multi-screen service.
The service is a VOD signal delivered to your iPhone over the broadcast spectrum. There’s no subscription requirement and it does not use you wireless data plan. Because broadcasters’ transmissions cover a wide area, a lucky iPhone user should be able to receive it throughout their coverage area, they just need a special receiver plug in and an app available through the iTunes store.
The two pilot stations plan to provide VOD versions of their programs and to make money from banner ads displayed during search.
Sounds cool. So, how does the service work?
Basically, the broadcasters are using excess bandwidth within their delivery streams to squeeze in the extra bits for the VOD content.
Television broadcasters use 6 MHz (megahertz) of spectrum per license using the original HDTV ATSC standard called A/53 ATSC. We typically think about this as supporting 19.2Mb/s (megabits per second). A/53 supports delivery of video using MPEG-2 compression. Modern multi-pass encoders produce a reasonably good HD signal in 10-12Mb/s, which leaves 7 Mb/s or so of the 19.2Mb/s total available for other things. Some stations currently use that bandwidth to put out standard definition multicast channels (those X.2 or X.3 channels you some time see). Some brave stations even try to multiplex 2 HD services in this space.
A newer “Mobile DTV” standard called A/153 was developed to sit on top of A/53 and permit a higher level of compression (MPEG-4 part 10 AVC) as well as enabling mobile, VOD and other applications. It’s a significant improvement over A/53 in that it supports 2-way services by using an internet backchannel–which makes things like subscriptions and audience measurement possible. The new VOD services announced use this new technology.
But where does the bandwidth come from?
Let’s look at an example: Hubbard Media, which has always been a bit on the bleeding edge, owns two stations in Minneapolis-St Paul. Per the chart on the right, you can see that they have combined the two stations under the label of channel 5.X. Through the KSTP transmitter they are delivering one full-time HD channel (KSTP 5.1) and an SD Multicast 5.7. My guess is that on average this totals 15Mb/s. Through KSTC transmitter they are delivering one part time HD channel (KSTC 5.2) and 3 SD channels (approximately averaging 15Mb/s-19Mb/s). All these are labeled within the channel 5 service. Between the two transmitters they have between 4-8 Mb/s available for VOD content delivery, depending upon the time of day. That 4-8Mb/s over a 24 hour period can result in as much as a 1/2 terabit (1 terabit is 1,000 gigabits) per day for delivery of VOD content. Because of the power of multicast and the efficiency of advanced compression, this is more than enough to deliver 100 hours of new content each day to a wide audience.
Imagine what is possible with multiple broadcasters providing the service in each market …
So, it sounds like the first steps toward a new low-cost mobile service, with commercial support, are on their way.
Good luck to Fischer and Hubbard – we love the concept.