Definition
AAC — AAC (Advanced Audio Coding) is a lossy audio codec standardized by MPEG in 1997 as a successor to MP3. It delivers better sound than MP3 at the same bitrate and is the standard audio track in most MP4 videos, Apple Music previews, iTunes downloads and many streaming services.
AAC is a codec, not a file type
You rarely see a file called ".aac". Instead, AAC audio sits inside a container: an MP4 video, an M4A audio file, or the segments of an HLS stream. That is why it is useful to separate the idea of a codec (how sound is compressed) from a container (how it is packaged).
How AAC compares
| Codec | Strengths | Where you meet it |
|---|---|---|
| AAC | Efficient, universally supported in modern devices | MP4 video, M4A, Apple devices, many streaming apps |
| MP3 | Plays on the oldest hardware | Music libraries, podcasts, car stereos |
| Opus | Excellent at low bitrates, royalty-free | WebM video, voice calls, browsers |
AAC has several profiles. AAC-LC (Low Complexity) is the everyday version used for music and video. HE-AAC adds tricks that keep voice and music listenable at very low bitrates, which is handy for internet radio. As a rough guide, AAC at about 128 kbps is fine for most listening, and around 256 kbps is the level iTunes has long used for music sales.
Why AAC matters when downloading videos
Most MP4 files you download already contain AAC audio, and many platforms offer an AAC stream alongside their video. This has two practical benefits:
- No extra quality loss for M4A. If the source audio is AAC, saving it as M4A can keep the original stream without re-encoding.
- Smooth playback. An MP4 with H.264 and AAC is the most widely playable combination for phones, TVs and editors.
Converting AAC to MP3 is possible and common, but it is transcoding between two lossy formats. Choosing a high MP3 bitrate such as 320 kbps keeps any extra loss very small.
AAC on SaveVidr
Choose M4A in the video to M4A tool when you want AAC audio for an iPhone, Mac or Android player, or pick MP3 in the MP3 converter for maximum device support. Only download audio you have the right to use.
FAQ
Frequently asked questions
Is AAC better than MP3?
At equal bitrates AAC generally sounds better than MP3, especially below about 192 kbps.
What bitrate is good for AAC?
About 128 kbps is fine for most listening, while 256 kbps is effectively transparent for most people with music.