The already crowded streaming music market now has to contend with Amazon.

The ecommerce company has introduced a music element to Prime, adding to the video and literary media offerings of the subscription service. Starting Thursday, Prime members will have access to Amazon's music service at no extra cost.

Prime Music, as Amazon is calling the service, will provide many of the same options as streaming services like Spotify or Beats. Users can stream an unlimited amount of music with no advertisements, play any song on demand as many times as desired and download any tracks that are available on the service.

The service will start out with more than a million songs, comparable to Pandora's library but far less than the 20 million Spotify claims. The service launches with iOS and Android applications, desktop options for Macintosh and Windows operating systems and as an automatic update on Kindle Fire devices. Any music downloaded as part of the service requires an active Prime membership to play. There is no free streaming option.

One major drawback of the initial version of the service will be the lack of recently released music. Steve Boom, vice president of digital music at Amazon, declined to provide specifics about the delays, but BuzzFeed previously reported that songs would need to be out for six months before coming to Amazon's streaming service. New music will still be available for purchase. Boom declined to provide specifics on the royalty arrangements for the music.

Prime Music includes a variety of contemporary and classic music, but users may find some artists missing. Amazon has deals with two of the major labels — Warner Music Group and Sony Music Entertainment — as well as a variety of other smaller rights holders. The major gap is Universal Music Group, which has not come to terms with Amazon.

Boom said he could not discuss any specifics but did say negotiations were ongoing to bring more music to the platform.

In a preview shown to Mashable by Boom, the service has many of the features that streaming music fans have come to expect. Prime Music provides playlists based on artist, genre, mood and personal taste. Users that have purchased music through Amazon will be able to integrate their existing libraries with the service.

One of the unique offerings from Prime Music is a synchronized lyrics feature that displays the words to songs as the music plays.

Image: Amazon

Amazon joins Apple as online music retailers that have joined the transition to streaming. With Apple's purchase of Beats, it now also operates a streaming service alongside its iTunes platform.

Boom said he was not worried about Amazon cannibalizing its music sales with Prime music, adding that streaming is clearly the future of music consumption.

"We've been in music for 16 years now. We've seen what everyone else has seen. Music consumption is changing," he said.

"We think this will bring more customers into our ecosystem overall," Boom added.

Attracting more customers to Prime is considered a winning proposition for Amazon by incentivizing customers to by more products from its core ecommerce business.

James McQuivey, a principal analyst for Forrester Research, said the company's foray into music is less about profit and more about giving customers reasons to shop with Amazon.

"Amazon is not interested in becoming a major player in the streaming music business, but that's probably okay because the music business is no longer really a business, it's a feature. In Apple's case, it's a feature of its devices, in Amazon's case, music will be a feature of its retail customer relationship," McQuivey said.

Amazon has been on a mission to expand the media offerings of its Prime subscription service. Launched in 2005, the service initially on included free two-day shipping on selected products. The company raised the price of the service for the first time in March, bringing the the cost to $99 per year. Boom said the price raise had nothing to do with the introduction of the music service.

It has been a bit or a rocky year for Amazon so far. Continued struggles to turn the type of profits investors hope for from its massive revenue stream have taken a toll on its stock price, which is down almost 16% in 2014. The company has also had to defend itself from critiques over its standoffs with book publisher Hachette and Warner Bros.

The introduction of music makes Prime the most diversified online media offering. Its individuals parts still trail the offerings of more specialized products, but Amazon has the advantage of not needing to rely on Prime as its primary source of income.

Prime currently costs $99 per year compared to $120 for Spotify, $100 for Beats, $108 for Netflix, $96 for Hulu and about $120 for a subscription to Oyster's book service.

Amazon has also moved beyond ecommerce in other ways. The company launched a streaming set top box in April and is expected to release a smartphone soon. "As you look around, you'll see Amazon expanding its relationship dramatically — adding music to video, investing in phones, set-top boxes, and probably other hardware," McQuivey said. "In the end, Amazon wants you to have 25 reasons a day to interact with it, because at least 5 of those will lead you to buy something. Nothing generates higher frequency interactions than mobile and music, which helps explain why Amazon is doing both."