Q: I recently bought an Apple AirPort Express and set up a set of speakers to give me AirPlay capability. It works perfectly from my iPhone, my iPad and from iTunes on my Windows 7 PC. Well, almost perfectly. Last night I rented an iTunes movie to watch on my PC and when I started the movie I realized I couldn’t select my AirPlay speakers. A quick Google search told me it is apparently not possible. Do you know if this is true? It seems crazy that I can play iTunes music, podcasts and radio through AirPlay, but not a movie.

– Nick

A: Unfortunately, this is indeed the case. AirPlay audio seems to be primarily intended for streaming things like music to a remote set of speakers located elsewhere in your house. Since watching a video on your PC generally requires you to be located in front of the PC, Apple is obviously (and incorrectly) making the assumption that you would only play your audio through directly connected speakers in this case. It’s also worth noting that even the Apple TV, which adds support for external AirPlay speakers in the recent 5.1 update also has the same limitation on streaming audio during video playback.

AirPlay can, of course, be used from iTunes to stream the entire video to an Apple TV, but even in this case there is no standard way to stream only the audio component while playing back video on a Windows PC itself.

This limitation with regard to AirPlay audio streaming has actually been an issue for years, going back to when the technology was known as AirTunes and supported audio only. Traditionally AirPlay/AirTunes audio streaming has been available solely from iTunes, and it is only recently that Apple has expanded it allowing Mac users to use an AirPlay destination as their system sound device in OS X Mountain Lion.

Fortunately an enterprising third-party developer, Rogue Amoeba, stepped in to fill the gap with an app known as Airfoil. Available in both Windows and Mac versions, Airfoil is a $25 software app that allows users to stream any audio from their Mac or PC to a remote AirPlay device. Airfoil also has the advantage of streaming audio only from specific applications, rather than redirecting your entire system audio stream to the AirPlay device, which makes it useful in some cases even for OS X Mountain Lion users who may be concerned about every system-generated beep and click coming out of their remote speakers.

Airfoil provides a number of other useful features that also help to justify the $25 asking price, including the ability to stream audio from your PC to multiple destinations, including AirPlay speakers, other computers or iPhone, iPad or iPod touch devices as well as to receive audio on your PC from other AirPlay sources.