Digital Briefs:, YouTube, Apple

- says it experienced explosive growth last year, up 204% in unique visitors, 147% in site visits, 219% in page views and 141% in time spent on site over 2007 levels.

- YouTube is letting users opt to have the audio in their videos muted rather than taken down completely if a record label makes a copyright claim against it. Other options include an AudioSwap tool that can replace the track win a pre-cleared one from the company's database.

- Apple stock is down $2.67 (3.3%) at mid-day after news broke late yesterday that the company's CEO Steve Jobs is taking a medical leave of absence.

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