What Is AAC? The Advanced Audio Coding Format Explained
AAC is the audio format behind Apple Music, iTunes, and YouTube — yet most people are never told what it actually is. Here's what AAC is, what it stands for, whether it's lossless, and how to convert AAC files free.
Need an AAC file in a more compatible format? Convert AAC to MP3 free — no software, no signup.
Convert AAC to MP3 →AAC is one of the most widely used audio formats in the world — it's what plays when you stream a song on Apple Music, watch a YouTube video, or listen to a track from the iTunes Store. This guide explains what the AAC format is, what AAC stands for, whether it's lossless, and how it compares to the other formats you run into every day.
What Is AAC?
AAC stands for Advanced Audio Coding. It's a lossy digital audio compression format — meaning it shrinks audio files by permanently removing sound data your ears are least likely to notice. It was designed as the successor to MP3, and at the same file size it generally sounds noticeably better, especially at lower bitrates.
AAC was standardized in the late 1990s as part of the MPEG-2 and MPEG-4 specifications, developed by a group that included Fraunhofer, Dolby, Sony, and AT&T. Today it's the default audio format for Apple Music, iTunes, YouTube, the PlayStation and Nintendo ecosystems, and most digital broadcasting.
What Does AAC Stand For?
AAC stands for Advanced Audio Coding. The "advanced" is relative to MP3: AAC uses smarter compression techniques — larger transform blocks, better handling of high frequencies, and more efficient stereo coding — to preserve more detail in the same amount of space.
Is AAC Lossless?
No — AAC is a lossy format. Like MP3, it achieves small file sizes by throwing away audio data, and that data cannot be recovered. AAC is simply more efficient at deciding what to discard, so it tends to sound better than MP3 at the same bitrate.
If you need true lossless audio — a perfect copy of the original — you want FLAC or ALAC instead. AAC is the right choice when you want great-sounding audio in a small, convenient file.
AAC Profiles: AAC-LC, HE-AAC and HE-AAC v2
Not all AAC is the same. The format defines several profiles tuned for different uses:
| Profile | Full name | Best for |
|---|---|---|
| AAC-LC | Low Complexity | The standard everywhere — iTunes, Apple Music, YouTube, streaming apps |
| HE-AAC | High Efficiency | Low-bitrate streaming and radio; adds spectral band replication |
| HE-AAC v2 | High Efficiency v2 | Very low bitrates; adds parametric stereo for voice and mobile |
For music, the file you're dealing with is almost always AAC-LC. HE-AAC mostly appears in streaming and broadcast where bandwidth is tight. We go deeper in our AAC-LC vs HE-AAC profiles guide.
.aac vs .m4a — The File-Extension Confusion
Here's where most people get tripped up. You'll see AAC audio saved with two different extensions:
.aac— a raw AAC audio stream..m4a— an MP4 container that holds AAC audio (and can store metadata like album art and tags).
The vast majority of AAC files you meet — everything from iTunes and Apple Music — are actually .m4a files. The codec inside is AAC; the .m4a is just the wrapper around it. (Confusingly, .m4a can also hold lossless ALAC audio — so the extension alone doesn't tell you the codec.) We break this down fully in AAC vs M4A: codec vs container.
How Does AAC Compare to Other Formats?
- AAC vs MP3 — AAC is the newer, more efficient codec; MP3 wins on universal compatibility.
- AAC vs FLAC — lossy AAC vs lossless FLAC: quality vs file size.
- AAC vs ALAC — Apple's lossy and lossless formats compared.
- AAC vs Opus — two modern codecs head to head.
- AC3 vs AAC vs EAC3 — music efficiency vs surround-sound support.
How to Open or Convert an AAC File
Every modern phone, computer and browser plays AAC natively, so you usually don't need to do anything. But if you need a file that plays on everything — older car stereos, basic MP3 players, some Android devices — converting to MP3 is the safe bet. Our free tools handle it in seconds, right in your browser, with no software or signup:
- AAC to MP3 converter — the universal-compatibility choice
- MP3 to AAC converter — smaller, Apple-friendly files
- AAC to WAV converter — for editing
- FLAC to AAC converter — shrink lossless libraries
Convert AAC files free — AAC to MP3, MP3 to AAC, and more. No account, no software, no limits.
Open the AAC Converter → AAC to MP3 →Explore the AAC Hub
Everything on the AAC format in one place — converters, format comparisons, and technical deep dives.
AAC Converters
- AAC Converter (all formats)
- AAC to MP3
- MP3 to AAC
- YouTube to AAC
- AAC to WAV
- AAC to MP4
- AAC to M4A
- AAC to FLAC
- AAC to OGG
- WAV to AAC
- FLAC to AAC
Format Comparisons
Deep Dive
Frequently Asked Questions
What is AAC?
AAC (Advanced Audio Coding) is a lossy digital audio compression format designed as the successor to MP3. It delivers better sound quality than MP3 at the same bitrate, which is why Apple, YouTube and most streaming services use it as a default format.
What does AAC stand for?
AAC stands for Advanced Audio Coding. It was standardized as part of the MPEG-2 and MPEG-4 specifications and is used across Apple Music, iTunes, YouTube and digital broadcasting.
Is AAC lossless?
No. AAC is a lossy format — it permanently discards some audio data to shrink file size. It is more efficient than MP3 at doing this, but for true lossless audio you need FLAC or ALAC.
What is the difference between AAC and M4A?
AAC is the audio codec; .m4a is a container file that usually holds AAC audio (it can also hold ALAC). So most .m4a files are AAC — the extension just labels the wrapper.
What is AAC-LC?
AAC-LC (Low Complexity) is the most common AAC profile, used by iTunes, YouTube and streaming apps. HE-AAC adds efficiency at low bitrates for streaming and broadcast.
How do I open or convert an AAC file?
Any modern device plays AAC natively. To convert it to a universally compatible MP3, use our free AAC to MP3 converter.