According to Archer, while the Amazon Prime Video app has excellent video quality, the app appears to be only outputting audio in PCM stereo.
PCM, or pulse-code modulation, is a form of digital audio commonly often used in computers and CDs. However, PCM is one of the oldest forms of digital audio formats. While audio purists often consider PCM superior because the sound is uncompressed, PCM is also two-channel audio, meaning it lacks the capability for surround sound. The more common Dolby 5.1, found alongside most video formats, is now preferred for most video streaming.
From Archer’s reporting, it appears that Amazon is aware of the issue, and may already have moved to cover its tracks.
“Making the situation even more strange is that when I first installed the Amazon Video app yesterday, shows were appearing with the 5.1 header information on them. But today that has mysteriously vanished, and shows are definitely only playing out in stereo,” Archer wrote.
Archer also points out the notable limitations that exist, given the more advanced capabilities of modern entertainment devices. “This isn’t exactly what you’d expect from one of the biggest profile apps on one of the AV world’s most expensive video streaming boxes,” he wrote. “Especially when the Apple TV 4K is capable of delivering 4K, HDR, Dolby Vision and 5.1 sound from so many other applications – including iTunes and Netflix.”
It is currently unclear why Amazon chose to reduce its audio quality in its Apple TV app to PCM stereo. Archer does point out that Amazon also does not provide the higher-quality Dolby Vision HDR in Europe, where he resides. Instead, European Prime Users must view Amazon’s content in the lower quality HDR10.