Apple

Want to watch a high-definition show from iTunes on an older external display? Good luck!

Some Mac users are teed off that they are getting error messages saying the iTunes movie they rented or bought can't be played on their display because it is not HDCP (High Digital Content Protection) authorized.

And some people are complaining they are only able to play certain standard definition iTunes content on their laptop or via an HDMI connection.

As a result, some Apple forum participants have threatened to boycott iTunes.

"And here we are now with Apple users who have spent thousands of dollars on Apple hardware (30" Cinema displays are not cheap!), buying films legitimately through Apple's store only to find themselves screwed when they just want to watch the film!" wrote "non-troppo" on the Apple Discussions Forum.

Forum participant Jim Beggans complained that Apple expanded the usage limitations of iTunes without updating the published usage terms.

"It is imperative that Apple address this customer concern with NEW terms of service (which will require them to offer some remedy for existing purchases) and clarify that HDCP is a now a standard part of their products regardless of which mode of the DisplayPort is in use," Beggans wrote.

ArsTechnica, which first covered the issue, reports that Apple's new MacBook is using DPCP, or DisplayPort Content Protection, which was developed by Philips.

The Mini DisplayPort connector used on Apple's new MacBooks and MacBook Pros uses DPCP to prevent iTunes files from being played on devices that are not compliant with either DPCP or HDCP, a copy-protection technology used with the HDMI standard. DPCP supports the HDCP technology, but is considered a stronger level of encryption according to the Video Electronics Standard Association (click for PDF) .

"While Apple's own Apple TV has used HDCP to protect video files playing from its HDMI port, this is the first time we've heard of Apple bringing HDCP DPCP to its hardware," David Chartier writes on ArsTechnica.

Basically, Apple is moving forward with a new standard that is not compatible with older displays. In the past, Apple has shown a willingness to forge ahead with new technology that doesn't always play nice with the older stuff, and the decision to use the Mini DisplayPort connector on the new MacBooks and MacBook Pros ensured that DPCP and HDCP would come along for the ride.

"Apple's compliance with HDCP--a necessary but appalling condition of the content companies that deliver the HD movies and TV shows--is beginning to close out the 'analog hole' and cause real aggravation for laptop owners with legitimate use cases, writes Michael Rose on The Unofficial Apple Weblog site.

Andy Foster sums the situation up on his Computer Blog: "In other words, the only way any of us can guarantee we can play the stuff we buy that is HD is to ensure we have the newest in hardware."

What does Apple have to say for itself? We don't know and likely won't. Apple representatives did not return repeated phone calls and e-mails seeking comment over two days.

(CNET News' Tom Krazit contributed to this report.)