Living standard — Last updated 2021/02/14
1. Overview
HE Audio is a community project to evolve podcast audio. By adopting current audio standards and using the best practices shared here, podcasters can create better-sounding podcasts at the same size of MP3-encoded podcasts.
Because listeners judge content quality in part on audio quality, HE Audio can help grow audiences for podcasts that use it, and can play a small part in growing podcasting as a whole. The transition to HE Audio is similar to the leap from AM to FM, or TV to HDTV.
The “HE” stands for “high efficiency”. That power can also be used to match MP3 quality at about half the file size—another clear benefit. For this use, HE Audio halves bandwidth costs for the podcaster and for listeners using metered connections, and potentially lets listeners store twice as much content on their phones, smartwatches, etc.
2. Background
MP3, the standard format for audio podcasts, is well over two decades old. During that time there have been many important advancements in audio technologies while podcast audio has literally been stuck in the 20th century.
In other digital mediums, MP3 has long since left behind in favor of AAC (Advanced Audio Coding). Every YouTube video uses it. Every song, TV show, and movie Apple sells uses it. Pandora streams AAC. All devices made in the last decade include hardware support for AAC decoding, making it ideal for battery-powered devices.
HE Audio’s “flavor” of AAC is High-Efficiency AAC (HE-AAC). It’s roughly twice as efficient as MP3. That allows creators and content distributors to choose (1) CD-like quality at typical MP3 bitrates, (2) MP3-like quality at roughly half the bitrate of MP3, or anything in-between.
It’s time for podcasting to make the leap to a modern audio format suitable for the next decade or two.
3. Encoding
HA Audio files must use a file extension of .m4a for audio-only podcasts, and .m4v for video podcasts.
Depending on the encoding bitrate, HA Audio must use either AAC, HE-AAC, or HE-AACv2 encoding.
| Profile | Bitrate | Codec | Channels |
|---|---|---|---|
| ULQ | ~16 kbps (CVBR) | HE-AACv2 | Mono |
| LQ | ~32 kbps (CVBR) | HE-AACv2 | Stereo |
| Prime | ~48 kbps (CVBR) | HE-AAC | Stereo |
| HQ | ~64 kbps (CVBR) | HE-AAC | Stereo |
| UHQ | ~96 kbps (CVBR) | AAC | Stereo |
4. RSS
HE Audio requires no changes to RSS.
RSS enclosures use an Internet-standard MIME type to declare the media type. For HE Audio (.m4a) files, this must be video/mp4. When using HA Audio in a video (.m4v) file, this must be video/mp4.
Appendix A: Platform support
Support for HE Audio formats (HE-AAC and HE-AACv2) is universal on modern media platforms and operating systems.
- All versions of Android support HE-AACv2 playback [Google]
- iOS introduced support for HE-AACv2 playback in iOS 4 (released 2010)
- Mac OS X introduced support for HE-AACv2 playback with iTunes 9.2 (released 2010)
- Adobe Flash Player introduced support for HE-AACv2 in 2007
- All versions of Windows Phone support HE-AACv2 playback
- All open source players support HE-AACv2 playback via FAAD2
Appendix B: References
- High-Efficiency Advanced Audio Coding [Wikipedia]
- High-Efficiency Advanced Audio Coding (HE-AAC) [Apple Technical Note]
MP3 AND AAC EXPLAINED, Karlheinz Brandenburg, Fraunhofer Institute for Integrated Circuits FhG-IIS A