Convert to AAC Format

MP3 and AAC both use perceptual coding — they discard audio data that the human ear is unlikely to perceive. AAC is more sophisticated: it supports up to 48 audio channels (vs MP3's 2), uses a larger transform block size (1024 samples vs 576), applies more accurate psychoacoustic modelling, and eliminates the patent-driven architectural constraints that limited MP3's design. The result is that AAC at 128 kbps typically sounds equal to or better than MP3 at 160 kbps.

AAC comes in several profiles: AAC-LC (Low Complexity) is the standard for music and general audio at bitrates above 64 kbps. HE-AAC v1 adds Spectral Band Replication (SBR) for efficient encoding at 32–64 kbps — used in DAB+ digital radio and some streaming services. HE-AAC v2 adds Parametric Stereo for encoding full stereo down to 24 kbps. AAC-ELD (Enhanced Low Delay) is optimised for real-time communication like FaceTime. For most conversion purposes, AAC-LC is the correct choice.

This is a common source of confusion. AAC is a codec — the algorithm that encodes and decodes audio. M4A is a container — the file wrapper that holds the encoded audio stream along with metadata. An M4A file almost always contains AAC-encoded audio (or ALAC for lossless). A raw .aac file contains the codec stream without a proper container. For iTunes and Apple Music compatibility, use the M4A container. For other use cases, both work fine.

Bitrate selection depends on your content type and destination:

• 96 kbps — Podcasts, spoken word, voice-only content. Excellent intelligibility, very small files.
• 128 kbps — General music for casual listening, good balance of size and quality.
• 192 kbps — Higher quality music, recommended for content where audio quality is noticed.
• 256 kbps — Apple Music standard. Considered transparent (audibly indistinguishable from lossless) by most listeners.
• 320 kbps — Maximum practical bitrate; marginally better than 256 kbps but significantly larger files.

AAC is the mandated audio codec for the MP4 container as defined by the ISO Base Media File Format standard. When exporting video from Adobe Premiere, DaVinci Resolve, or Final Cut Pro, the audio track is encoded to AAC by default. If you are preparing a standalone audio file to be muxed into an MP4 at a later stage, converting it to AAC first ensures the audio encoding step happens on your terms — with your preferred bitrate and quality settings rather than the video editor's default.