Playing right into our ongoing discussion about the ever-increasing quality of streaming, Netflix has, via its Tech Blog, lifted the hood on something that it's calling "Adaptive High Quality Audio." In short, for networks that can handle it, Netflix is upping the Dolby Digital+ bitrate of its 5.1 and Atmos audio content from 192 kbps to 640 and 768 kbps, respectively.

Our high-quality sound feature is not lossless, but it is perceptually transparent. That means that while the audio is compressed, it is indistinguishable from the original source. Based on internal listening tests, listening test results provided by Dolby, and scientific studies, we determined that for Dolby Digital Plus at and above 640 kbps, the audio coding quality is perceptually transparent. Beyond that, we would be sending you files that have a higher bitrate (and take up more bandwidth) without bringing any additional value to the listening experience.

This isn't an across-the-board change for all users on all systems, though. Just as Netflix uses adaptive algorithms to deliver video to its customers in the best quality with as little buffering as possible, the company is moving from static streaming to adaptive streaming for audio, as well.

The benefits are obvious in this simple case, but extending it to our broad streaming ecosystem was another challenge. There were many questions we had to answer in order to move forward with adaptive streaming for audio.

What about device reach? We have hundreds of millions of TV devices in the field, with different CPU, network and memory profiles, and adaptive audio has never been certified. Do these devices even support audio stream switching?

• • We had to assess this by testing adaptive audio switching on all Netflix supported devices.
  • We also added adaptive audio testing in our certification process so that every new certified device can benefit from it.

Once we knew that adaptive streaming for audio was achievable on most of our TV devices, we had to answer the following questions as we designed the algorithm:

• • How could we guarantee that we can improve audio subjective quality without degrading video quality and vice-versa?
  • How could we guarantee that we won't introduce additional rebuffers or increase the startup delay with high-quality audio?
  • How could we guarantee that this algorithm will gracefully handle devices with different performance characteristics?

To read more about this upgraded audio experience, read the full post on the Netflix Tech Blog.

Additional Resources
• Read Engineering a Studio Quality Experience With High-Quality Audio at Netflix on the Netflix Tech Blog.
• Read Performance Versus Lifestyle: From a Reviewer's Perspective at HomeTheaterReview.com.
• Read Netflix and Amazon Are Killing Ultra HD Blu-ray (And I Feel Fine) at HomeTheaterReview.com.