CONVERT AAC → AU (AAC to AU)
Fast, secure AAC to AU conversion. No registration required.
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HOW TO CONVERT AAC → AU
Provide the audio file
Drag the AAC onto the uploader. Files up to 25 MB run on the free tier without registration; paid plans go up to 2 GB.
ffmpeg handles the conversion
Our ffmpeg-based pipeline reads sample rate and channel layout, then writes a matching AU with ID3 tags intact.
Save the output
Click to download the AU. Batch uploads are bundled into a ZIP for single-click retrieval.
Why this pair exists — AAC is the Advanced Audio Codec, more efficient than MP3 and ubiquitous in modern streaming. Ergo, the AU route. A AAC to AU conversion is typically about compatibility: some players refuse AAC, many accept AU. The audio payload makes the round trip with minimal artefacts when bitrate is left at sensible defaults. Drop a AAC file into the uploader and the AU comes back in seconds. A quick refresher — AAC is the Advanced Audio Codec, more efficient than MP3 and ubiquitous in modern streaming. By contrast, AU is the Sun/NeXT audio format, a historical PCM container still found in older pipelines.
Why convert AAC to AU
Moving from AAC to AU usually buys compatibility or a friendlier file size. For spoken-word content the difference is inaudible; for high-resolution music pick the highest bitrate the AU codec supports to avoid compounding compression.
AAC vs AU — Technical specifications
Side-by-side comparison of the technical details.
AAC
- MIME type
- audio/aac
- Extensions
- .aac, .m4a, .mp4 (container-dependent)
- Standard
- ISO/IEC 14496-3
- Variants
- AAC-LC, HE-AAC, HE-AACv2, AAC-LD, xHE-AAC
- Sample rates
- 8-96 kHz
- MIME Type
- audio/aac
- Extension
- .aac
- Category
- Audio Files
- Full Name
- AAC Audio
- Conversion Engine
- FFMPEG
AU
- Extensions
- .au, .snd
- MIME Type
- audio/basic
- Extension
- .au
- Category
- Audio Files
- Full Name
- Sun AU Audio
- Conversion Engine
- FFMPEG
- MIME types
- audio/basic, audio/au, audio/x-au
- Header
- 24 bytes (magic, offset, size, encoding, rate, channels, info)
- Codecs
- PCM 8/16/24/32-bit, µ-law, A-law, IEEE float
- Byte order
- Big-endian
| Specification | AAC | AU |
|---|---|---|
| MIME type | audio/aac | — |
| Extensions | .aac, .m4a, .mp4 (container-dependent) | .au, .snd |
| Standard | ISO/IEC 14496-3 | — |
| Variants | AAC-LC, HE-AAC, HE-AACv2, AAC-LD, xHE-AAC | — |
| Sample rates | 8-96 kHz | — |
| MIME Type | audio/aac | audio/basic |
| Extension | .aac | .au |
| Category | Audio Files | Audio Files |
| Full Name | AAC Audio | Sun AU Audio |
| Conversion Engine | FFMPEG | FFMPEG |
| MIME types | — | audio/basic, audio/au, audio/x-au |
| Header | — | 24 bytes (magic, offset, size, encoding, rate, channels, info) |
| Codecs | — | PCM 8/16/24/32-bit, µ-law, A-law, IEEE float |
| Byte order | — | Big-endian |
AAC vs AU — Strengths and limitations
What each format does best, and where it falls short.
AAC Strengths
- Better quality than MP3 at equal bitrate — the industry standard since 2000s.
- Universally supported on every smartphone, OS, and browser.
- Efficient on battery thanks to widespread hardware decoding.
- Scales from 8 kbps speech (HE-AACv2) to lossy-transparent 320 kbps.
- Five-channel + LFE surround support out of the box.
Limitations
- Patent-encumbered — encoders have licensing fees, which is why open alternatives (Opus, Vorbis) exist.
- Slightly more complex to encode than MP3.
- Raw .aac streams carry no seek index — tooling often prefers M4A/MP4 containers.
AU Strengths
- Trivially simple format — 24-byte header, then samples.
- µ-law 8-bit variant fits hours of speech in kilobytes.
- Stable since 1988; every major audio library reads it.
- Streaming-friendly: size field is optional.
Limitations
- Aging — obsolete outside legacy and compatibility scenarios.
- No metadata beyond a single annotation string.
- No native multi-channel surround support.
Quality & Compatibility
Sample rate, channel layout and bit depth are preserved by default: a 44.1 kHz stereo AAC becomes a 44.1 kHz stereo AU. Metadata — title, artist, album, cover art — travels where both formats support it. Protected DRM content cannot be converted legally and is rejected.
Tips for Best Results
- Check the podcast host specification before choosing bitrate — some mandate CBR 64 kbps, others accept VBR up to 192 kbps.
- Preserve ID3 tags by editing them before conversion; Mp3tag and MusicBrainz Picard handle round-tripping cleanly.
- If the AAC is 24-bit studio audio, the AU at 16-bit is sufficient for listening; higher is wasted on consumer playback gear.
Frequently Asked Questions
Lossy-to-lossy conversions (most combinations) re-compress the audio, which technically introduces some loss. At a 192 kbps or higher target it is inaudible on normal equipment. Lossy-to-lossless conversions freeze the existing quality but cannot improve it; lossless-to-lossy transcodes are only as good as the target bitrate you choose.
For voice content (podcasts, audiobooks, lectures) 128 kbps is indistinguishable from higher bitrates. For music, 192-256 kbps covers most listening; 320 kbps is the ceiling for AU and the right choice for audio you plan to edit further. Above that, prefer a lossless target instead.
Yes. Title, artist, album, year and cover art travel from the AAC container to the AU container automatically where both formats support them. If a tag field has no AU equivalent, it is dropped silently. Use any tag editor (Mp3tag, MusicBrainz Picard) to fine-tune afterwards.
AAC Audio
Source formatAAC is a lossy audio codec that delivers better sound quality than MP3 at similar bitrates. It is the default audio format for Apple Music, YouTube, and most streaming services.
Sun AU Audio
Target formatAU is a simple audio format from Sun Microsystems, commonly used on Unix systems.
Going the other way? Convert AU back to AAC with the same engine.
Common Use Cases
Share across platforms
Send AU files to anyone without worrying about whether they have the right software for AAC.
Embed in documents
Drop AU output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
AU often produces smaller files than AAC for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
AAC vs AU — Typical file sizes
Approximate file sizes for common scenarios.
- Speech podcast (64 kbps) 1 MB/min
- 3-min music track (128 kbps) 3 MB
- 3-min music track (256 kbps) 6 MB
- 10-second clip (8-bit µ-law, 8 kHz) 80 KB
- 10-second clip (16-bit PCM, 44.1 kHz stereo) ~1.7 MB
Lossless 24-bit Hi-Res Audio or Full Discographies?
Converting pristine FLAC/ALAC collections while preserving 192kHz master dynamics without exhausting mobile bandwidth? Dedicated multi-threaded workstation converters handle entire folders instantly.
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High-throughput enterprise pipeline for files up to 2,048 MB, 50-file batches, ISO PDF/A, and priority processing.
Lossless batch chain processing preserving full ID3v2 metadata tags and embedded artwork.
Multi-CPU discography conversion with AccurateRip CRC verification and DSP mastering.
Related comparisons
See these formats side by side to understand which fits your use case best.
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