Spotify, the Swedish music streaming company, has parked its tanks higher up Apple’s lawn with the launch of an “offline” mode. The new feature, which was first developed for mobile phone users, allows subscribers to store up to 3,333 songs as playlists on their computers. Previously users could only listen to tracks, not store them.

The move is significant because it means that for the first time Spotify customers will be able to build up a library of music stored on their home computer which can then be searched through and listened to at any time. The music will be available even in the absence of an internet connection, making it the near equivalent of a large iTunes library.

The songs will also be cheaper than buying music from iTunes. For a monthly subscription of £10 users can download thousands of tracks — a so-called “all you can eat” deal — that could mean songs cost a fraction of the 79p per track that Apple charges. There is a catch, though: the music will remain available only so long as the monthly subscription is paid. Fail to keep it up and the tunes will disappear.

For Spotify the move marks a new attempt to get listeners to pay for music. The company made its name by offering free music to listeners in return for them hearing the occasional advert, much like a radio broadcast. The strategy has been wildly successful, particularly in Britain: the company claims that in July, it had 2.7m users in the UK, and that between February and July those users streamed one billion tracks.

By enabling users to store the tracks, Spotify hopes they will be willing to upgrade from the free service and pay the subscription. It is a bold move. “As a business they are just finishing the first leg of a marathon,” warns Mark Mulligan, an analyst at Forrester Research, who tracks the music industry. “Building a free audience is the comparatively easy part. Building a large, paying audience is where most others have tried and failed.”

Apple will be watching the move closely. And music fans will be looking at the cheapest way yet to build up digital music libraries. Just so long as they keep up their subscriptions.

The streaming rivals

Last.fm Free streaming “radio” service that recommends tracks based on music you like.

Verdict: Good way to discover new music, but no downloads and lower sound quality than rivals.

Napster £5 a month for unlimited streaming from a library of 8m tracks, plus five MP3 downloads to own.

Verdict: Slick but Windows only.

Sky Songs Launching before Christmas; unlimited streaming and a set number of downloads.

Verdict: May require subscription to TV services.

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