The short answer
- AAC is a compressed audio coding format that stores encoded sound, with playback dependent on support for the file’s container and coding configuration.
- On Windows, try opening the file in iTunes, which supports AAC-encoded audio. On Mac, choose an audio player that explicitly supports the file’s AAC configuration and packaging. On iPhone or iPad, try AAC playback in a compatible audio app; Apple documents AAC playback on these devices, but individual files still require matching support. If playback fails, check the container and coding configuration before assuming corruption.
- Treat an unfamiliar AAC file with care. IANA states that private tags can contain arbitrary material, including executable content, which receivers must never execute. Protection depends on the decoder or player. Decoding can substantially increase data size. An audio/aac object has no internal signature or encryption, so confidentiality and integrity require external protection.
AAC files: opening, playback and conversion
AAC stands for Advanced Audio Coding. IANA lists ISO/IEC 13818-7 and ISO/IEC 14496-3 among its related standards. The .aac extension corresponds to ADTS packaging. The audio/aac media type also covers LATM/LOAS, for which .loas is recommended. AAC coding support alone therefore does not establish support for every file.
Converting AAC to MP3 can reduce audio quality because both are compressed formats. When possible, create the new encoding from the original audio source. AAC can also be converted to WAV or AIFF; Apple states that conversion from compressed to uncompressed audio generally introduces no perceptible additional quality loss. This does not restore information already lost during compression.
How to open it
On Windows, try opening the file in iTunes, which supports AAC-encoded audio. On Mac, choose an audio player that explicitly supports the file’s AAC configuration and packaging. On iPhone or iPad, try AAC playback in a compatible audio app; Apple documents AAC playback on these devices, but individual files still require matching support. If playback fails, check the container and coding configuration before assuming corruption.
On Windows, try opening the file in iTunes, which supports AAC-encoded audio. On Mac, choose an audio player that explicitly supports the file’s AAC configuration and packaging. On iPhone or iPad, try AAC playback in a compatible audio app; Apple documents AAC playback on these devices, but individual files still require matching support. If playback fails, check the container and coding configuration before assuming corruption.
Converting AAC to MP3 can reduce audio quality because both are compressed formats. When possible, create the new encoding from the original audio source. AAC can also be converted to WAV or AIFF; Apple states that conversion from compressed to uncompressed audio generally introduces no perceptible additional quality loss. This does not restore information already lost during compression.
File safety
Treat an unfamiliar AAC file with care. IANA states that private tags can contain arbitrary material, including executable content, which receivers must never execute. Protection depends on the decoder or player. Decoding can substantially increase data size. An audio/aac object has no internal signature or encryption, so confidentiality and integrity require external protection.
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
Converting AAC to MP3 can reduce audio quality because both are compressed formats. When possible, create the new encoding from the original audio source. AAC can also be converted to WAV or AIFF; Apple states that conversion from compressed to uncompressed audio generally introduces no perceptible additional quality loss. This does not restore information already lost during compression.
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is an AAC audio file?
AAC means Advanced Audio Coding, a compressed audio coding format. IANA associates the .aac extension with ADTS packaging and registers audio/aac as its media type.
How do I open AAC files on Windows?
Try opening the file in iTunes on Windows. Apple documents AAC playback in iTunes, but the individual file’s container and coding configuration must also be supported.
How do I play AAC files on Mac?
Open the file with an audio player that explicitly supports its AAC configuration and container. The .aac extension is associated with ADTS; support for AAC encoding alone does not guarantee playback of every file.
How do I play AAC files on iPhone?
Try opening the file in a compatible audio app. Apple documents AAC playback on iPhone, but successful playback of a particular file depends on its container and coding configuration.
Why will an AAC file not play or report an unsupported format?
The player may not support the file’s container or AAC coding configuration. Check both before concluding that the file is damaged. An extension or an ADTS sync marker alone cannot establish file validity.
AAC versus MP3: which audio format should I use?
Both are compressed audio formats. Choose the format supported by your intended player. If another encoding is needed, use the original audio source where possible, because converting between AAC and MP3 can reduce quality.
Does converting AAC to MP3 lose audio quality?
It can. Converting between compressed formats can reduce quality. Apple recommends importing again from the original source when you need another encoding.
How do I convert AAC to WAV without additional perceptible quality loss?
Use an audio converter that accepts the AAC file and exports WAV. Apple states that compressed-to-uncompressed conversion generally causes no perceptible additional quality loss; it does not recover detail already lost through compression.
Are AAC audio files from an unfamiliar sender safe to open?
The format name does not guarantee safety. IANA warns that private tags can contain executable material, which a receiver must not execute. Use a player that provides appropriate decoder protections.
Does the AAC ADTS sync word prove that a file is valid?
No. ADTS uses the 12-bit sync word 0xFFF as a frame marker. IANA lists the magic number as N/A, so this marker alone proves neither complete file validity nor safety.
Related formats
Sources
IANA — audio/aac media type registration · IANA 官方媒体类型注册记录
Apple — Choose import settings in iTunes on PC · Apple 官方支持文档
Apple — Save a copy of a song in a new file format · Apple 官方 iTunes 用户指南