The Huffman prophecy

By Julian Clover
November 13, 2009 10.22 UK

Ofcom has told the BBC it cannot compress the data associated with its terrestrial HD transmissions. The solution? Move to Switzerland, writes Julian Clover.

Until the past few weeks few people in the TV business will have heard of David Huffman, the PHD student at MIT who in 1952 published a paper entitled A Method for the Construction of Minimum-Redundancy Codes. His work has been used in assorted technologies, such as the fax machine, and is now at the centre of a debate over the encryption of data within terrestrial HD signals.

The BBC, perhaps at the behest of the Hollywood wants to restrict the licensing of the Huffman tables to manufacturers that adhere to the Digital Television Group’s Copy Management specification, a plan put on hold by Ofcom. The licences would be freely available, but you would still have to apply for one, keeping a check on who was doing what and giving manufacturers something else to worry about for the technological island that is the UK.

One organisation that is keeping an eye on proceedings is the Open Rights Group, a member funded organisation that has described the move as a “blatant attempt to impose encryption of TV through the back door”. Its comments may have hit home as Ofcom extended its consultation through to a period that will clearly run into the soft launch of Freeview HD on December 1. The Open Rights Group is also campaigning against Phorm’s targeted advertising technology and Lord Mandleson’s plans to disconnect internet subscribers thought to be participating in illegal filesharing. The involvement of Open Rights Group may have led to an increase in consumer responses, far outweighing responses from broadcasters or manufacturers, which were conspicuous by their absence.

The issue stems from the concern that the BBC might have an HD movie on – in reality the BBC shows few films on its high definition channel – that can then be recorded onto a Freeview+ receiver with hard disk allowing anyone to take that content and re-encode it. The British public now have to grapple with the concept of rights windows that can see BBC content appear on iTunes just a week after it television premiere. By using Huffman the BBC could bypass the normal conditional access options that could bring the perception of working with one proprietary CA provider over another.

Strictly speaking this is about the compression of some of the SI data, rather than encryption of the video content itself. If a manufacturer doesn’t have the licence, then BBC HD would not appear in the EPG. It can be assumed that the BBC will apply HDCP on the HDMI output on DTT in the same way it does on Freesat. This begs the question if copy protection is used on the Freeview, then why not on Freesat?

It is already possible to record HD content through Freesat+ products using the internal hard drive and to external devices like the Panasonic Freesat+ Blu-ray product, however in this case the broadcaster controls which programmes can and can’t be recorded through a data flag in the broadcast stream. As far as we know, Huffman is not in place over satellite.

Entertainingly it is possible to sit in Switzerland and record the domestic version of BBC HD through the local operator Cablecom, which has continued to practice of relaying free-to-air broadcasts from the UK to its subscribers.