Netflix adopts xHE-AAC variable bitrate audio codec on Android

Netflix is rolling out an update on the Android version of its app that promises to bring “studio-quality” sound to your daily TV or movie watching experience.

The company is switching over to xHE-AAC or Extended High Efficiency AAC, which is a newer version HE-AAC that the company has been using so far. It was introduced back in 2012 by Fraunhofer IIS and was primarily designed for use in online streaming and broadcasting services due to its high compression ratio and efficiency, with bit-rates as low as 6kbps for mono and 12kbps for stereo, going up to 500kbps and beyond. It’s also a variable bit-rate codec that can change based on the connection strength and bandwidth.

The other main feature of xHE-AAC is that it features mandatory loudness and dynamic range control at the encoder level, generating multiple profiles of dynamic range meta data for different listening setups — such as playing on a phone’s speaker, listening through headphones, or through a home theater setup — and then switches automatically to the relevant one.

Netflix claims this improves the discernibility of dialogue even when watching to content on a phone’s speaker in noisy environments as the volume has been normalized to the dialogue and the overall dynamic range has been compressed to stay above the ambient noise levels. It’s not clear, however, how Netflix determines what the ambient noise levels are to do these adjustments.

In its A/B testing, Netflix found that most people preferred the audio quality of the new codec, and were less likely to switch to using earphones when watching on their phone as the compensation applied through the phone speaker made it clear enough.

The new codec is only available on Android now, which has become Netflix’ favorite platform to experiment new features with, but the company says it will be bringing it to other platforms that support the codec. Considering almost all platforms, including iOS, macOS, and Windows, already support xHE-AAC, it probably shouldn’t take long for them to be switched to the new codec.