Virgin's cable service "bandwidth constrained"

Virgin Media content chief Malcolm Wall has admitted that bandwidth constraints will hold back the launch of linear high definition channels on the media group's cable TV service.

Wall told Brand Republic that Virgin Media is planning to launch more linear high definition channels - Virgin TV currently only carries BBC HD - but explained: "We are bandwidth constrained. We have enhanced head ends for HD channels. But the main focus with HD is [video on demand] and it’s our belief there is an appetite for HD film. However, we hope to add HD channels on a selective basis."

Before NTL and Telewest merged into what was subsequently renamed Virgin Media, NTL had planned to offer high definition services using the more efficient MPEG-4 compression technique, and delivered to a new fleet of MPEG-4 multi-room digital video recorders. However, post-merger, the combined firm opted to continue using Telewest's TV Drive DVR - now known as the V+ - which is capable only of receiving MPEG-2 channels, and as such the high definition services take up vastly more bandwidth than if they had been encoded in MPEG-4.

Cable operators in the US are already moving to MPEG-4 and switched video - where bandwidth for linear TV channels is allocated on an on-the-fly, on demand basis - in order to deliver HD services ranging from HBO's 26 premium film channels to high-def simulcasts of CNN. The technology was adopted by HomeChoice, now Tiscali TV, in August 2005, and forms part of Ofcom's HD migration plan for Freeview.