Convert MPEG to AU — Free Online Tool
Convert MPEG video files to Sun AU audio format, extracting the audio stream and re-encoding it as 16-bit big-endian PCM — the default codec for AU files. This is useful for pulling uncompressed audio from legacy MPEG broadcasts or DVD-compatible video for use on Unix systems or early audio pipelines.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your MPEG file here
or click to browse
Free — no uploads, no signups. Your files never leave your browser.
Settings
Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
MPEG files typically carry MP2 or MP3 audio compressed alongside MPEG-1 or MPEG-2 video. Because the AU format is audio-only and does not support video, the video stream is discarded entirely during this conversion. The compressed audio (usually MP2 at 192k) is fully decoded and then re-encoded as raw 16-bit signed big-endian PCM (pcm_s16be), which is the standard codec for Sun AU files. This means the output is uncompressed audio with no lossy codec artifacts introduced beyond what was already present in the MPEG source — but file sizes will be significantly larger than the original audio track since PCM carries no compression.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles all demuxing, decoding, and encoding operations. In the browser version, this runs via FFmpeg.wasm compiled to WebAssembly — no server is involved. |
-i input.mpeg
|
Specifies the input MPEG file. FFmpeg will demux this container to extract the MPEG-1 or MPEG-2 video stream and the MP2, MP3, or AAC audio stream for processing. |
-c:a pcm_s16be
|
Sets the audio codec to signed 16-bit big-endian PCM, which is the standard encoding for Sun AU files. This decodes the compressed MP2 (or other) audio from the MPEG source into raw, uncompressed PCM samples stored in big-endian byte order as required by the AU format. |
output.au
|
Defines the output filename with the .au extension. FFmpeg uses this extension to select the Sun AU muxer, which writes the minimal AU header followed by the raw pcm_s16be audio data. The video stream from the MPEG input is automatically discarded because the AU container is audio-only. |
Common Use Cases
- Extracting uncompressed audio from archived MPEG broadcast recordings for ingestion into Unix-based audio editing or analysis tools that natively read AU files
- Preparing audio from MPEG-1 or MPEG-2 video sources for use in legacy Sun Microsystems workstation software or vintage Unix audio applications that require the .au format
- Converting MPEG soundtrack audio to PCM AU for use in Java applications, which have historically used Sun AU as a natively supported audio format via javax.sound.sampled
- Stripping audio from DVD-compatible MPEG-2 files into a simple, header-light AU format for streaming over early or constrained Unix-based network audio pipelines
- Archiving the audio component of MPEG video in an uncompressed format (PCM) to avoid further generation loss when the audio will be re-encoded later into another format
- Debugging or verifying the decoded audio content of an MPEG file by converting it to raw PCM AU, which can be inspected sample-by-sample with standard Unix audio tools
Frequently Asked Questions
The conversion does not introduce any new lossy compression — AU with pcm_s16be is uncompressed PCM audio. However, the MPEG source already contains MP2 or MP3 audio, which is lossy, so any artifacts from that original compression are already baked in. Decoding MP2 to PCM and writing it as AU is a lossless operation on the decoded signal, meaning the AU file is an accurate uncompressed representation of what the MPEG audio sounded like.
MPEG audio tracks (MP2 at 192k, for example) are heavily compressed. When decoded to pcm_s16be for the AU format, the audio becomes raw uncompressed samples — typically 16 bits per sample at the original sample rate (often 44100 or 48000 Hz). A 1-minute stereo audio track at 48000 Hz in PCM uses roughly 11 MB, compared to about 1.4 MB at 192kbps MP2. The video stream is also discarded, but the PCM expansion more than offsets that reduction.
No. The Sun AU format has an extremely minimal header that contains only technical parameters: encoding type, sample rate, channel count, and an optional short ASCII annotation field. It does not support ID3 tags, Vorbis comments, or any structured metadata. Any title, artist, or date information stored in the MPEG file will be lost during conversion to AU.
Yes. The AU format supports several codecs beyond pcm_s16be, including pcm_mulaw, pcm_alaw, pcm_s8, and pcm_u8. You can change the codec in the FFmpeg command by replacing '-c:a pcm_s16be' with '-c:a pcm_mulaw' or another supported codec. Mu-law and A-law are 8-bit companded formats historically used in telephony and will produce much smaller files at the cost of dynamic range.
On Linux or macOS, you can use a shell loop: 'for f in *.mpeg; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.mpeg}.au"; done'. On Windows Command Prompt, use: 'for %f in (*.mpeg) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au"'. This applies the same conversion logic — discarding video and encoding audio as 16-bit big-endian PCM — to every MPEG file in the current directory.
FFmpeg preserves the sample rate from the source MPEG audio track by default. MPEG-1 audio commonly uses 44100 Hz, while MPEG-2 (including DVD-compatible content) often uses 48000 Hz. The resulting AU file will carry that same sample rate in its header. If you need to target a specific sample rate — for example, 8000 Hz for telephony AU files — you can add '-ar 8000' to the FFmpeg command before the output filename.
Technical Notes
The Sun AU format was designed for simplicity: a fixed-size or variable-size header followed by raw audio data, with big-endian byte ordering reflecting its Sun SPARC workstation origins. This tool uses pcm_s16be (signed 16-bit big-endian PCM), which is the most common and widely compatible AU codec and preserves the full dynamic range of CD-quality audio. The source MPEG file's video stream (MPEG-1 or MPEG-2) is automatically dropped because AU is a pure audio container — FFmpeg handles this implicitly without requiring an explicit '-vn' flag in this case, since the output container cannot hold video. One important limitation: AU does not support multiple audio channels beyond what its header encoding allows, and while stereo is broadly supported, exotic multi-channel MPEG audio configurations may not map cleanly. Additionally, AU files have no chapter markers, no subtitle support, and no way to store loop points or cue data. For very long MPEG source files, the resulting AU file can be extremely large; at 48000 Hz stereo pcm_s16be, audio runs at approximately 192 KB per second.