Netflix has finally given attention to optimizing its audio streaming technology in the same way its adaptive video switching system can seamlessly recalibrate video bitrates while a stream is underway. The company has significantly raised the quality of its audio streams to a rate it claims is now indistinguishable from studio quality sound.
In a week where streaming technology is under the critical microscope following a much-anticipated Game of Thrones episode suffering due to encoding and compression problems, Netflix has delivered a well-timed announcement revealing long-awaited fundamental improvements to how it streams sound.
Although Netflix has been delivering 5.1 and Dolby Atmos audio streams for several years it has strictly limited the bitrate quality of those audio tracks. Often an audio stream would not exceed a bitrate of 192 kbps, and anyone who has experienced a Netflix stream through a top-end home entertainment set-up will understand how frustrating the sound delivery has been.
Netflix now claims it can deliver 5.1 audio streams of up to 640 kbps, and Dolby Atmos streams up to 768 kbps. Of course, these bitrates are nowhere near equal to studio masters, but Netflix says extensive internal testing has found these levels equate to "perceptually transparent" thresholds, meaning an average listener would not be able to tell the difference between an uncompressed studio master track and the Netflix top-quality compressed stream.
Perhaps even more important is the announcement that the same adaptive streaming technique the company applies to video is now being used for audio. When watching a Netflix stream the video track will continually increase or decrease its bitrate in relation to the real-time network conditions. This helps avoid any constant buffering issues from spotty internet connections. Audio tracks however, have never been adaptive, with the audio bitrate initially calibrated at the start of a stream, and never changing once a video is playing.
Now, Netflix has worked to transfer its adaptive streaming technology to the audio tracks of its content so it can ramp its audio bitrates up or down in real-time according to individual network conditions, without pausing to rebuffer. According to a blog penned by the Netflix engineering team behind the innovation, it took well over a year of work to fine tune the algorithm so it seamlessly functioned on the wide variety of devices people tend to watch Netflix through.
"By using our listening tests and scientific data to choose an optimal 'transparent' bitrate, and designing an adaptive audio algorithm that could serve it based on network conditions, we've been able to enable this feature on a wide variety of devices with different CPU, network and memory profiles: the vast majority of our members using 5.1 should be able to enjoy new high-quality audio," the tech team explains in a Medium blog post.
Watch the Netflix team discuss the path to implementing its high-quality audio streams in the video below.
Source: Netflix