HOLLYWOOD — RealNetworks’ efforts to enable downloading of music it sells through its online store onto Apple’s iPod were rebuffed last week as Apple declined to open up its market-leading digital music player, which works only with its own iTunes Music Store.RealNetworks CEO Rob Glaser’s emailed alliance proposal to Apple CEO Steve Jobs was leaked to the New York Times last week, but Jobs wasn’t interested, Real said. Other digital music companies are dying to get access to the iPod. In its first quarter earnings Wednesday, Apple reported that sales of the music player skyrocketed over 900% from last year to 807,000 units — more than the number of Macintosh computers sold by the company. Real, meanwhile, announced that in the first quarter it reached a total of 450,000 subscribers to its music subscription services, including Rhapsody, which offers unlimited streaming. Microsoft is rumored to be working on technology that would allow subs to put music from subscription services onto mobile devices as long as they continue to pay a monthly fee, which many believe would provide a strong challenge to the 99¢ download market that Apple’s iTunes dominates.