The rising popularity of the Blu-Ray DVD format has been illustrated by the record-breaking sales of The Dark Knight.
Blu-Ray's triumph over HD DVDs was shrouded in controversy with the release of the PS3 games console seen as a means of promoting the format, but The Dark Knight's sales figures on the high-definition Blu-Ray format have shown it to be a well-loved fixture of many homes.
Some 600,000 Blu-ray copies of The Dark Knight were sold on its first day of release - Iron Man sold 500,000 Blu-rays in its first week, and The Matrix 780,000.
Ron Sanders, president of Warner Home Video, commented: "In the first two days across those three territories, Blu-Ray disc sales are running between 25 per cent and 30 per cent of total sales, which is a massive number.
"We had expected Blu-Ray to account for a significant percentage of sales, but not quite this high, which speaks well for the format. It's really catching on with consumers."
First-week sales figures have now been collated and The Dark Knight has sold almost two million copies worldwide, with one million coming from US consumers.
Its popularity has been so underestimated that the Blu-Ray version of the film has sold out on Amazon.com, with no signs of the stocks being replenished before Christmas.
The late Heath Ledger was nominated for a best supporting actor Golden Globe for his performance as The Joker in The Dark Knight.