Opus vs AAC: which codec should you use?

Opus is the more efficient codec: in published listening tests it beat AAC at around 64 and 96 kbps, and its delay is low enough for live calls. AAC is the more established one: it is Apple's standard music format and plays on nearly every device. At high bitrates such as 256 kbps both sound transparent to most listeners. Choose Opus for voice, calls and web apps; choose AAC for Apple devices and wide compatibility.

Is Opus better than AAC?

At low and medium bitrates, usually yes. In the Hydrogenaudio listening tests, Opus beat HE-AAC at about 64 kbps and was slightly better than AAC at about 96 kbps. At 192 kbps and above, both are transparent for most listeners, so compatibility matters more than the codec.

Does YouTube use Opus or AAC?

Both. YouTube streams Opus audio in WebM to browsers and apps that support it, and also serves AAC audio in MP4. Wikipedia notes that YouTube Music Premium uses 256 kbps Opus. Which one you get depends on your device and app.

Which one is better, LDAC or AAC?

They are Bluetooth codecs rather than file formats. LDAC is Sony's codec on Android (part of Android since 8.0) and runs at 330, 660 or 990 kbps depending on signal. AAC is what Apple's AirPods use. LDAC can carry more data with a strong connection, but both are lossy, and the result depends on your headphones and phone.

Can I convert AAC to Opus?

Yes, but it means decoding one lossy format and encoding another, which adds some loss. If you have the original as WAV or FLAC, encode Opus from that instead. Our WAV to Opus and FLAC to Opus converters do this in your browser.

Opus vs AAC: Which Codec Is Better?

Opus and AAC are the two strongest lossy audio codecs in everyday use. AAC is older, standardized in the late 1990s, and became the default music format of Apple's world. Opus arrived in 2012, designed to handle speech and music in one codec with very low delay. They overlap on the web, on phones and in streaming, and each owns its own territory elsewhere. This guide compares them on quality, efficiency, delay and support, and ends with a simple way to choose.

The short answer

Voice, calls and live audio: Opus, clearly.
Low bitrates (64 kbps and under): Opus.
Apple devices, iTunes-style libraries and wide device support: AAC.
Music at 192–256 kbps: effectively a tie for most listeners, so pick on compatibility.

How the codecs are built

AAC (Advanced Audio Coding) was standardized by MPEG in 1997, first as MPEG-2 Part 7 and then as part of MPEG-4. It was designed as MP3's successor. Like MP3, it uses a frequency transform (the MDCT) and a model of human hearing to decide what to keep. It comes in profiles: AAC-LC, the standard for music; HE-AAC, which adds spectral band replication to rebuild high frequencies at low bitrates; and HE-AAC v2, which also adds parametric stereo for very low bitrates.

Opus, published by the IETF as RFC 6716 in 2012, is a hybrid. It combines SILK, a speech codec developed at Skype, with CELT, a low-delay music codec from Xiph.Org. The encoder can use either one or both at once, so it can switch smoothly between a voice call at a few kbps and stereo music at hundreds. It runs from 6 to 510 kbps, supports frame sizes from 2.5 to 60 ms, and is open and royalty-free.

Quality and bitrate efficiency

The listening tests most often cited come from the Hydrogenaudio community and are linked from the Opus project's comparison page:

At about 64 kbps: Opus scored ahead of two HE-AAC encoders and Vorbis.
At about 96 kbps: Opus scored slightly ahead of two AAC-LC encoders, and clearly ahead of Vorbis and a 136 kbps MP3.

The pattern is consistent: Opus's lead is biggest at low bitrates and shrinks as bitrate rises. At 192 to 256 kbps, both are transparent for most listeners on most equipment, meaning they cannot reliably tell the file from the original. At those bitrates, encoder quality, the source recording and your headphones matter more than the codec.

AAC's quality also depends heavily on the encoder. AAC is a standard with several implementations, and they do not all sound the same at the same bitrate.

Delay

Opus was built for conversations. Its default algorithmic delay is 26.5 ms (with 20 ms frames), and a low-delay mode goes down to 5 ms. MDN lists AAC's delay as anywhere from 20 to 405 ms, depending on the profile and settings. HE-AAC's extra processing adds delay, so the low-bitrate AAC profiles are the slowest.

For a song, a podcast or a video, delay does not matter. For voice and video calls, live streaming with interaction, music played together over the internet, and games, it decides the choice. That is why the WebRTC standard requires Opus support.

Device and platform support

AAC is supported almost everywhere:

Apple: every iPhone, iPad, Mac and Apple TV. AAC is the iTunes Store's standard format, and AirPods use the AAC Bluetooth codec.
Android: AAC-LC in .mp4, .m4a, .3gp and ADTS .aac files on every version.
Browsers: MDN describes AAC in MP4 as supported by all major browsers.
Hardware: many car stereos, TVs and portable players read AAC, though fewer than read MP3.

Opus support is wide but newer:

Browsers: Chrome 33+, Firefox 15+, Edge 14+. Safari support grew in stages, with full support on iOS 18.4 and later.
Android: playback since Android 5.0 (WebM and Matroska files), Ogg files since 7.0, and the .opus extension since Android 10.
Apple: Opus in CAF files since iOS 11 and macOS High Sierra; .opus playback in the Files app since iOS 17; Ogg in Safari since iOS 18.4 and macOS 15.4.
Hardware: many car stereos and older speakers and players do not read Opus.

Where each is used

AAC: the iTunes Store and Apple Music, the soundtracks of most MP4 videos, Apple's Bluetooth audio, and many broadcast and streaming systems.

Opus: WebRTC calls in browsers, Discord, WhatsApp, Zoom and Signal (as listed on Wikipedia), YouTube's WebM audio streams, and web apps and games that need efficient or low-delay audio.

Bluetooth: a different question

People often ask "Opus or AAC?" when they mean which Bluetooth codec their headphones use. On standard Bluetooth headphones, the codecs are SBC, AAC, aptX or LDAC, not Opus. Apple devices send AAC to AirPods, and Android phones can use AAC, aptX or LDAC if the headphones support them. All of these are lossy. Apple's own support page says Bluetooth connections are not lossless. Our guide on lossless audio over Bluetooth explains the codecs.

Bitrates that work

Xiph.Org's recommended Opus settings are 10–24 kbps for voice calls, 24–32 kbps for audiobooks and podcasts, 64–96 kbps for music streaming and 96–128 kbps for music you keep. It describes 128 kbps VBR as "pretty much transparent." For AAC, MDN recommends at least 96 kbps for stereo music, and the iTunes Store sells music at 256 kbps. So Opus at around 128 kbps and AAC at around 256 kbps are both safe high-quality choices; the Opus file is about half the size.

Which should you choose?

Situation	Choose
Voice or video calls, live audio	Opus
Voice notes or spoken word at low bitrates	Opus
A web app or game you control	Opus
Music library for iPhone, Mac or Apple Music	AAC (256 kbps)
Files that must play on most phones, TVs and cars	AAC (or MP3 for older hardware)
Music at 192 kbps or more, on modern devices	Either; choose by compatibility
A master copy you will edit or convert again	Neither: keep WAV or FLAC

Converting between Opus and AAC

Going from one lossy codec to the other always stacks a second round of loss on top of the first. The cleanest route is to encode each format from the same lossless original:

To Opus: WAV to Opus or FLAC to Opus.
To AAC: FLAC to AAC or WAV to AAC.
When only the lossy file exists: convert at a generous bitrate. For a device that reads neither format, Opus to MP3 and AAC to MP3 give a file that plays almost anywhere.

All of these run in your browser with FFmpeg and never upload your files. Free users get 5 conversions per month. The output is limited to the first 10 seconds as a preview, with a 20MB input file size limit. Upgrade to Pro for unlimited, full-length conversions.

The bottom line

Opus is the more efficient and more flexible codec, with clear wins at low bitrates and for anything live. AAC is the safer file to hand to an Apple device or an unknown player, and at 256 kbps it sounds as good as Opus to most listeners. Use Opus where you control playback or need low delay, AAC where compatibility and Apple's ecosystem matter, and keep a lossless master if you will ever need both.