Convert MPG to AU — Free Online Tool
Convert MPG video files to AU audio format, extracting and re-encoding the audio stream as uncompressed 16-bit big-endian PCM — the native encoding of Sun's AU format. This is ideal for pulling clean, lossless-quality audio from MPEG-1/2 video files for use on Unix systems or legacy audio pipelines.
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FFmpeg Command
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Estimated output:
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DownloadHow It Works
MPG files typically carry MP2 (MPEG Layer II) or occasionally MP3/AAC audio alongside an MPEG-1 or MPEG-2 video stream. During this conversion, FFmpeg discards the video stream entirely and decodes the compressed MP2 audio from the MPG container, then re-encodes it as PCM signed 16-bit big-endian (pcm_s16be) audio wrapped in a Sun AU container. The AU format uses a minimal fixed header and stores raw PCM samples, so the output is uncompressed — expect file sizes roughly 5–10x larger than the original MPG audio track depending on the source bitrate and duration.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary, the open-source multimedia processing engine that handles reading the MPEG-1/2 program stream, decoding the MP2 audio, and writing the AU output. |
-i input.mpg
|
Specifies the input MPG file. FFmpeg will demux this MPEG-1/2 container, identifying both the video stream (mpeg1video or mpeg2video) and the audio stream (typically MP2) contained within it. |
-c:a pcm_s16be
|
Instructs FFmpeg to encode the output audio as signed 16-bit big-endian PCM, which is the native and default encoding for the Sun AU format. This decodes the compressed MP2 audio from the MPG and stores it as raw, uncompressed samples in the AU file. |
output.au
|
Sets the output filename with the .au extension, which tells FFmpeg to use the Sun AU muxer. The video stream from the MPG is automatically dropped since AU is an audio-only container. |
Common Use Cases
- Extracting audio from archived VCD or DVD-sourced MPG recordings for use in Unix-based audio processing workflows that expect AU files
- Converting broadcast MPEG-2 video captures to AU format for ingestion into legacy Sun Solaris or early Java-based audio applications
- Pulling the MP2 audio from an MPEG-1 video and converting it to uncompressed PCM AU for precise sample-level editing without generation loss
- Preparing audio from MPG training or archival videos for use with older Unix command-line audio tools like `play` or `sox` that natively handle AU files
- Stripping and converting the audio track from VCD-format MPG files into AU for use as sound assets in retro or Unix-era software development projects
Frequently Asked Questions
There is a one-time decode step where the compressed MP2 audio from the MPG file is decoded to raw PCM before being stored in the AU container. The resulting AU file uses uncompressed pcm_s16be (16-bit big-endian PCM), so no further compression is applied — the output is as close to lossless as 16-bit PCM allows. However, because the original MP2 audio was already lossy, any artifacts introduced during the original MPG encoding are baked in and cannot be recovered.
The AU format stores raw uncompressed PCM audio samples, unlike the MP2 codec inside MPG which is a compressed lossy format typically encoded at 128–192 kbps. Uncompressed 16-bit stereo audio at 44.1 kHz requires approximately 1.4 Mbps, meaning a 3-minute MPG audio track compressed at 192 kbps will expand to roughly 30 MB as a raw PCM AU file. This is expected behavior — AU is not a compressed format.
No. The AU format is a pure audio container and cannot store video streams. FFmpeg automatically drops the video stream when writing to a .au output file, extracting only the audio. If you need to keep the video, you would need to choose a video-capable output format instead.
Yes. The AU format supports several PCM encodings including pcm_s8, pcm_u8, pcm_alaw, and pcm_mulaw. You can override the default by adding -c:a pcm_mulaw to the command, for example: ffmpeg -i input.mpg -c:a pcm_mulaw output.au. Mu-law and A-law encodings are common in telephony applications and produce significantly smaller files at the cost of reduced dynamic range.
On Linux or macOS, you can use a shell loop: for f in *.mpg; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.mpg}.au"; done. On Windows Command Prompt, use: for %f in (*.mpg) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au". This applies the same pcm_s16be encoding to every MPG file in the directory and names each output AU file after the corresponding input.
The Sun AU format has an extremely minimal header and offers virtually no standardized metadata fields beyond a basic annotation string. FFmpeg may attempt to write a simple text annotation, but structured metadata such as title, artist, or chapter information from the MPG source will not be preserved in the AU output. If metadata preservation is important, consider extracting to a format like FLAC or WAV instead.
Technical Notes
The Sun AU (.au) format was developed by Sun Microsystems and became common on Unix workstations and early Java applets due to its simplicity — it consists of a 24-byte minimum header followed by raw audio data. The default codec chosen here, pcm_s16be, stores 16-bit signed integers in big-endian byte order, which reflects the big-endian architecture of the SPARC systems AU was designed for. This byte order is the reverse of WAV's little-endian PCM, so AU files are not directly byte-compatible with WAV even at the same bit depth. The input MPG container, based on MPEG-1/2 program stream or transport stream, typically encodes audio as MP2 at 32–384 kbps; this is fully decoded to PCM during conversion with no sample rate conversion unless explicitly requested. Note that AU does not support multiple audio tracks, subtitles, chapters, or any video — all of which MPG can carry. The format does support basic streaming due to its sequential data layout, which was useful for early HTTP audio streaming before MP3 became dominant.