On-demand archive programming will account for 25% of all TV viewing in the UK by 2009, a BBC boss has said.
Wildlife programme Planet Earth has been released by the BBC
Television archives will form a third of broadcasters' revenues by 2009, said the BBC's head of new media and technology, Ashley Highfield.
Speaking at the Edinburgh TV Festival, Mr Highfield also predicted that a primetime hit would attract fewer than 5m viewers in five years from now.
The "long tail effect" is viewers' interest in old and niche programming.
The trend has already been noticed on internet site Amazon, where archive and material of special interest already accounts for a growing amount of sales.
"One person's grit is another's pearl," said Mr Highfield about the importance of making archive material more accessible to the public.
Ex-BBC boss Greg Dyke outlined plans to open the archive in 2003
The BBC is currently working on the digitisation of its vast archives and allowing the public to use them as part of the Creative Archives project.
The process is slow because complicated rights issues have to be overcome with each clip.
Content from the BBC's Natural History Unit was released in March, which as part of the scheme can be re-used in non-profit programme-making.
Mr Highfield also said that television on-demand will accelerate with improved search methods, internet recommendations and cross-promotion.
He added that "significant" parts of the BBC archive would become available as early as next year.
The BBC director said he thought that in five years time the only events to win big terrestrial audiences would be the World Cup and Royal weddings.