BBC's Quested responds to BBC HD debate

BBC principle technologist Andy Quested has started a lengthy technical response to criticism of the picture and sound quality on BBC HD.

Last week, the BBC's director of archive content Roly Keating responded to Paul Eaton's sustained campaign about the quality of BBC HD output. He also promised that Quested would respond soon in greater detail.

Writing on the BBC Internet Blog, Quested claimed that BBC HD, which reaches its second birthday this weekend, offers "one of the widest ranges of programmes you could find anywhere in a single HD package".

However, he added: "No one is going to say it's all been perfect and in the past I have had to make a couple of very confessional blog posts when we've, 'just got it wrong'. We take every aspect of the channel very seriously and consider you to be a valuable asset when it comes to problem solving, trouble shooting or just 'plain' talking."

After new encoders were introduced by the BBC on August 5, the bitrate on BBC HD dropped from 16Mbs to 9.7Mbs, a reduction of nearly 40%. Viewers subsequently reported various problems with picture quality and sound on the channel.

Quested said that encoder testing "takes a long time" because it's not only about picture quality, but also checking for compliance with MPEG4 standards. The technology further has to be tested for compatibility with set-top-boxes from a variety of manufacturers, including specific requirements for the satellite platforms.

Running until December 11, Quested intends to issue a series of daily technical breakdowns, starting with the audio issues affecting the channel.

In the first post, he said that BBC technical teams make sure that BBC HD's AV sync is always within 5ms and check it regularly to maintain the status. Initially, this led to smooth running of the channel's audio.

Unfortunately, the steady performance gave way to a "couple of weeks where nothing seemed to work properly", starting with holes in the audio on Strictly Come Dancing.

After the holes later appeared on broadcasts of the Electric Proms, the problem was diagnosed as "machine failure" and Quested claimed that it was "unlikely to be repeated".

However, human failure was the cause of a different issue with Doctor Who after the programme went out in stereo rather than full surround sound audio.

"After a bit of investigation we discovered someone had routed one of the server ingest video tape players to another area and changed the audio replay options to a non-standard mode," said Quested.

"When the machine was routed back to its normal role the audio set-up was not reset and the next programme in the stack for loading was Doctor Who."

He added: "Machine or circuit failure is one thing that we all have to accept happens occasionally and we apologise if it does. But I have made it clear we must stick to agreed practice and procedures because they are there to prevent errors.

"I hope the action we have taken will keep the audio on the channel running smoothly with no more mistakes."

Quested will issue a further correspondence about the history of high definition encoders on Monday.