The world's fourth-largest music company reported a fiscal second-quarter net loss of $27 million, or 19 cents a share, compared with a loss of $7 million, or 5 cents a share, a year earlier.
Excluding one-time items, it lost 10 cents per share, in line with analysts' average forecast, according to Reuters Estimates.
Revenue declined 2 percent to $784 million from $796 million.
Weak music sales were the result of a tough comparison with strong results a year earlier, as well as overall market challenges as music disc sales slide, Warner Music said.
"The recorded music industry remains challenged by piracy and changing consumption patterns in the shift from physical sales to new forms of digital music," the company said in a statement.
Major sellers in the quarter included titles from Madonna, Red Hot Chili Peppers and Gerald Levert.
The company said that by the end of its fiscal year it would incur restructuring charges of $65 million to $80 million as it cuts costs and shifts resources into digital distribution methods.
It said it expects to reduce its head count by about 400 employees. It said some of its savings will be offset by new hirings and other investments.