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Apple recommends xHE-AAC for streaming of all audio assets

During this year’s Worldwide Developer Conference, xHE-AAC was featured in three separate sessions on HLS streaming to Apple devices.

Due to the global pandemic, Apple’s 2020 Worldwide Developer Conference (WWDC) was held online with free access for everyone. The sessions were recorded and made available to the public. xHE‑AAC, which is natively supported by the latest Apple operating systems, was prominently featured in three sessions about HLS streaming.

During the session entitled “Deliver a better HLS audio experience,” Simon Goldrei from Apple’s Streaming Media team introduced the latest member of the AAC codec family, which is new to HLS. He also provided developers with Apple’s recommendations on audio bit rates for xHE-AAC-based streaming services. These range from “data rates as low as 24 kilobits per second all the way up to the maximum that we have recommended [for] AAC, at 160 kilobits per second for stereo,” Goldrei stated. He went on to outline the various motivations for service providers to use xHE-AAC, such as reaching users on low-bandwidth networks and on devices with restricted data rates.

Goldrei also highlighted the importance of the loudness and dynamic range control (DRC) metadata. The MPEG-D DRC standard provides loudness control for xHE-AAC to play back content at a consistent volume. In addition, it offers dynamic range control processing to provide the best possible user experience for listening on any platform, in any environment. Underscoring Apple’s commitment to open standards, Goldrei explained that Apple’s recommendations are consistent with the new ANSI/CTA 2075 standard (“Loudness Standard for Over the Top Television and Online Video Distribution for Mobile and Fixed Devices”), as well as CMAF (Common Media Application Format), which aims at unifying media encodings between MPEG-DASH and HLS. “The takeaway is that DRC is becoming more relevant throughout our industry, and your inclusion of this metadata is the way forward,” Goldrei concluded.

Watch the session: https://developer.apple.com/videos/play/wwdc2020/10158/

A session entitled “What’s new in streaming audio for Apple Watch,” led by Suresh Koppisetty from Apple’s Streaming Media team, disclosed that xHE-AAC decoding will be added to the AVPlayer for watchOS7. The reason for this is its ability to “deliver equivalent quality at lower bit rates – or you can choose to deliver higher quality at equivalent bit rates to other codecs in the AAC family.” Koppisetty also mentioned that when streaming to a smart watch, which has to function under highly variable network conditions, “we should aim to deliver high-quality audio content with as low a bit rate as possible.” He concluded by stating: “Hence, we recommend using xHE-AAC for encoding all your audio assets.”

Watch the session: https://developer.apple.com/videos/play/wwdc2020/10636

In the “Improve stream authoring with HLS Tools” session, Eryk Vershen from Apple’s HLS Streaming team talked to developers and service providers about xHE-AAC and multi-channel audio codecs. He explained how they should be used in HLS playlists consisting of video and audio content where the latter can come in various language versions and channel configurations. The session also gave specific hands-on advice regarding how developers can prioritize xHE-AAC-encoded versions of the audio content over legacy codecs, using the newly introduced SCORE attribute. In the example given during the session, Vershen emphasized that “USAC [xHE-AAC] is going to sound better. We really want to choose HE-AAC only if we’re on some device that can’t play USAC. We fix this with the SCORE attribute. We give the USAC variants higher scores so they are preferred. This allows the USAC to function like a mutually exclusive codec.”

Watch the session: https://developer.apple.com/videos/play/wwdc2020/10225

About xHE-AAC

xHE-AAC is the latest member of the MPEG AAC audio codec family. Fraunhofer played a substantial role in the development of xHE-AAC and the MPEG-D DRC standard. Professional xHE-AAC encoder software is available directly from Fraunhofer IIS or its streaming equipment partners. xHE-AAC and MPEG-D DRC patents are included in the AAC patent licensing program administered by VIA Licensing at no additional cost.

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