Blu-ray, the format identified by Hollywood as the successor to the DVD, has grown in popularity but is not close to making up the ground left by the decline of its predecessor: consumers spent $750m on Blu-ray discs in 2008 compared with $21.6bn on DVDs. The Dark Knight is the best-selling Blu-ray title, with about 2m copies, but sales of other titles are being held back because too few Blu-ray players have been sold.
