Virgin Mobile's mobile TV service will only use 59 kbps per TV channel

8th September 2006

Many of you will no doubt have seen on the BBC News that Virgin Mobile will be launching a new mobile TV service that's transmitted over the DAB system — to be precise, the service will be transmitted on the Digital One national commercial DAB multiplex.

One thing that you're probably not aware of, though, is how bad the picture and audio quality will be on these mobile TV channels, because, as can be seen on the Wohnort website (scroll down to the Digital One multiplex to see the service bit rates used), which lists the DAB multiplex configurations, each mobile TV channel will only be using a bit rate of 64 kbps! In fact, it's even lower than 64 kbps, because stronger error correction coding has to be added, because DAB's error correction coding isn't strong enough for mobile TV transmissions, and the actual bit rate of the mobile TV channel, taking into consideratin the additional error correction, is at most:

64 kbps x (188 / 204) = 59 kbps

That's 59 kbps in total to encode both the video and the audio of the TV channel. I've not seen the service yet, but I don't need to see it to know that using just 59 kbps it will look and sound unspeakably bad.

You've just got to think about it for a moment to realise how ridiculously low 59 kbps is to encode both video and audio: video typically requires far higher bit rates than audio (TV channels typically use a bit rate that is 15-times higher than radio stations), so even taking into consideration the fact that mobile TV screen sizes are very small, the video bit rate will still need to be higher than the audio bit rate. So say the ratio of the video to audio bit rate is around 4 to 1, that would mean that the video video bit rate would be around 47 kbps and the audio bit rate would be 12 kbps. These are just ridiculously low bit rate levels.

I used to subscribe to the 3 mobile phone network, and they offered video downloads which had terrible picture and audio quality, and I'd expect the new Virgin Mobile mobile TV service to be of similar quality to that.

In comparison, mobile TV channels on the DVB-H commercial service in Italy and in the numerous DVB-H trials around the world are using bit rates of around 250 - 384 kbps for mobile TV channels.

How unusual that awful quality is being provided on the DAB system in the UK...