Convert AU to OGA — Free Online Tool
Convert AU (Sun Audio) files to OGA format, transcoding raw PCM audio streams into Vorbis-encoded Ogg containers. This is ideal for modernizing legacy Unix audio files into an open, compressed format suitable for web and media players.
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FFmpeg Command
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Estimated output:
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DownloadHow It Works
AU files store uncompressed PCM audio (typically 16-bit big-endian signed integers, as used on Sun/Unix systems) with a minimal fixed header. During conversion, FFmpeg decodes the raw PCM stream from the AU container and re-encodes it using the libvorbis encoder, producing a compressed Vorbis audio stream wrapped in an Ogg container with the .oga extension. This is a full transcode — not a remux — because the source codec (PCM) and destination codec (Vorbis) are entirely different. The Vorbis encoder applies perceptual lossy compression, significantly reducing file size while preserving perceived audio quality. The resulting OGA file is streamable, supports rich metadata tagging, and is playable in virtually all modern open-source and web-based audio players.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the core multimedia processing engine that handles decoding the AU file's PCM audio and re-encoding it as Vorbis inside an Ogg container. |
-i input.au
|
Specifies the input AU file. FFmpeg reads the AU header to determine the PCM encoding (e.g., 16-bit big-endian signed), sample rate, and channel count before decoding the raw audio stream. |
-c:a libvorbis
|
Selects the libvorbis encoder for the audio stream, converting the uncompressed PCM data from the AU file into lossy Vorbis-compressed audio — the standard codec for OGA files and a significant step from raw PCM toward a modern open-source compressed format. |
-q:a 4
|
Sets the Vorbis variable bitrate quality to level 4 on a 0–10 scale, targeting approximately 128 kbps — a balanced default that delivers noticeably smaller files than the original uncompressed AU while maintaining good perceptual audio quality for most source material. |
output.oga
|
Specifies the output filename with the .oga extension, which signals FFmpeg to wrap the encoded Vorbis stream in an Ogg container — the audio-only variant of the Ogg format, distinct from .ogg which may contain video. |
Common Use Cases
- Modernizing archival Unix system audio samples or sound effects stored as AU files for use in modern web applications or HTML5 audio elements
- Compressing large uncompressed AU audio recordings from legacy Sun workstations to save storage space using Vorbis lossy compression
- Converting AU voicemails or telephony recordings (often stored as PCM µ-law or A-law) into OGA for distribution on open-source or Linux-centric platforms
- Preparing early internet-era AU audio content for podcast or streaming platforms that prefer open container formats over proprietary alternatives
- Migrating audio assets from Unix-based game development pipelines or sound design tools that export AU files into a compressed, metadata-capable format
- Creating Ogg Vorbis audio files from raw PCM AU sources for use in open-source game engines like Godot, which natively support OGA/Vorbis
Frequently Asked Questions
Yes, this conversion introduces lossy compression. AU files typically contain uncompressed PCM audio (lossless by nature), while OGA with Vorbis encoding applies perceptual compression that discards audio data deemed inaudible. At the default quality setting of -q:a 4 (roughly 128 kbps variable bitrate), the result is transparent for most listeners. If you need lossless output, consider using the FLAC codec within the OGA container instead of Vorbis.
AU files store raw PCM audio with no compression — a 1-minute stereo file at 44.1 kHz 16-bit PCM takes roughly 10 MB. Vorbis compression in the OGA container uses psychoacoustic modeling to reduce file size by 80–90% with minimal perceptible quality loss. The size reduction is entirely expected and is one of the primary reasons to make this conversion.
Yes. OGA supports FLAC as a lossless audio codec, which would preserve the full quality of the original PCM data from the AU file. To do this, change the command to use -c:a flac and remove the -q:a flag, since FLAC is lossless and does not use a quality scale. The resulting file will be larger than a Vorbis-encoded OGA but smaller than the original AU file due to FLAC's lossless compression.
The -q:a flag controls Vorbis quality on a scale from 0 (lowest, ~64 kbps) to 10 (highest, ~500 kbps), with 4 as the default (roughly 128 kbps). To increase quality for critical listening, change it to -q:a 6 or -q:a 8. To produce a smaller file for voice or telephony content originally recorded in AU format, -q:a 2 or -q:a 3 is typically sufficient since those AU recordings often had limited bandwidth to begin with.
AU files have a very minimal header that can include a text annotation field, but in practice most AU files contain no meaningful metadata tags. OGA/Ogg Vorbis supports rich Vorbis Comment metadata (title, artist, album, etc.), but since the AU source rarely contains any, the output OGA file will typically have empty tags. You can add metadata manually using FFmpeg's -metadata flag in the command.
The command as shown processes a single file. To batch convert all AU files in a directory on Linux or macOS, you can use a shell loop: for f in *.au; do ffmpeg -i "$f" -c:a libvorbis -q:a 4 "${f%.au}.oga"; done. On Windows PowerShell, use: Get-ChildItem *.au | ForEach-Object { ffmpeg -i $_.Name -c:a libvorbis -q:a 4 ($_.BaseName + '.oga') }. This is particularly useful if you have a large archive of legacy AU audio files to modernize.
Technical Notes
AU is a straightforward format: a fixed-size or variable-size header followed by raw audio data, with big-endian byte ordering inherited from Sun SPARC architecture. FFmpeg supports all common AU PCM variants including pcm_s16be (standard), pcm_s8, pcm_u8, pcm_alaw, and pcm_mulaw — the last two being common in telephony. All of these are decoded to raw PCM internally before Vorbis encoding begins. The libvorbis encoder is the reference implementation and produces fully compliant Ogg Vorbis streams. One important consideration: if your AU source was recorded at an unusual sample rate (Sun systems sometimes used 8000 Hz for voice or 22050 Hz for system sounds), libvorbis will encode at that same sample rate without resampling unless you explicitly add -ar to the command. OGA does not support multiple audio tracks or subtitle streams, but it does support chapter markers. The Ogg container's streaming-friendly page-based structure means OGA files can be progressively decoded, unlike the headerless nature of the AU format which requires the full file to determine audio properties.