Extract Audio from RM to AU — Free Online Tool
Extract audio from legacy RealMedia (.rm) files and convert it to Sun AU format, encoding the audio stream as 16-bit big-endian PCM (pcm_s16be) — a lossless, uncompressed representation ideal for Unix environments and archival workflows. This tool runs entirely in your browser with no file uploads required.
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FFmpeg Command
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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
RealMedia files typically carry audio encoded with AAC or MP3 (via libmp3lame), both of which are lossy compressed formats. During this conversion, FFmpeg discards the video stream entirely and decodes the compressed audio, then re-encodes it into uncompressed 16-bit big-endian PCM audio wrapped in a Sun AU container. Because the source audio is lossy (AAC or MP3), the output PCM is a lossless representation of that already-compressed signal — not a restoration of the original uncompressed audio. The AU format uses a minimal header structure, which makes it especially straightforward to parse on Unix-based systems and in audio processing pipelines.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which handles the entire process of reading the RealMedia container, demuxing its streams, decoding the compressed audio, and writing the Sun AU output. |
-i input.rm
|
Specifies the input RealMedia file. FFmpeg reads the .rm container and identifies the available streams — typically a video stream (encoded with MJPEG) and an audio stream (encoded with AAC or MP3). |
-vn
|
Disables video output, telling FFmpeg to ignore the video stream from the RealMedia file. This is required because Sun AU is a pure audio format with no support for video data. |
-c:a pcm_s16be
|
Sets the audio codec to 16-bit signed big-endian PCM, which is the native and most compatible audio encoding for Sun AU files. This decodes the compressed AAC or MP3 audio from the RealMedia source into uncompressed PCM form. |
output.au
|
Specifies the output filename and container. The .au extension tells FFmpeg to wrap the PCM audio in a Sun AU container with the simple fixed-length header that Unix audio tools and legacy systems expect. |
Common Use Cases
- Archiving audio tracks from legacy RealMedia streaming recordings (e.g., early 2000s internet radio or lecture captures) into an uncompressed, widely parsable format for long-term preservation
- Feeding audio from old RealMedia files into Unix-based audio processing tools (like SoX or legacy DSP pipelines) that natively read Sun AU format
- Extracting dialogue or narration from historical RealMedia educational content for analysis or transcription workflows that require raw PCM input
- Recovering audio from .rm files when the video stream is corrupted or unneeded, producing a clean, container-agnostic PCM file
- Preparing RealMedia audio content for import into vintage Unix workstations or emulators that support AU but not modern compressed formats
- Stripping the audio from RealMedia promotional or broadcast content from the late 1990s for use in multimedia research or digital humanities projects
Frequently Asked Questions
No — converting from RealMedia to AU will not recover quality lost during the original AAC or MP3 encoding. The audio in your .rm file was already compressed when it was created, discarding audio data that cannot be recovered. The AU output will be an uncompressed PCM copy of that already-lossy signal, which means it will be larger in file size but will not sound better than the source. Think of it as freezing the quality at whatever level it was in the original RealMedia file.
Sun AU format was designed for simplicity and Unix compatibility, and its most widely supported codec is pcm_s16be — 16-bit signed PCM in big-endian byte order, which reflects the byte order of SPARC and Motorola-based Unix workstations where the format originated. AU does support a-law and mu-law compressed codecs, but pcm_s16be is the default because it offers the most straightforward compatibility across tools that read AU files. If you need a smaller file, you'd be better served by converting to a format like FLAC or MP3 instead.
Yes. The AU format supports several PCM variants including pcm_mulaw, pcm_alaw, pcm_s8, and pcm_u8 in addition to the default pcm_s16be. To use mu-law encoding (common in telephony), you would modify the command to: ffmpeg -i input.rm -vn -c:a pcm_mulaw output.au. Keep in mind that mu-law and a-law encodings are lossy and optimized for voice-range audio at 8kHz, so they may not be appropriate for music or broadband audio content from your RealMedia file.
Almost certainly not. The Sun AU format has an extremely minimal header that includes only basic technical parameters (sample rate, channel count, encoding type) and an optional annotation field — it has no standardized support for ID3-style metadata tags. Any RealMedia metadata such as title, author, or copyright information embedded in the .rm file will be lost during conversion. If metadata preservation matters, consider converting to FLAC or OGG instead, which have robust tagging support.
The browser tool processes one file at a time, but if you have many .rm files to convert, you can run the displayed FFmpeg command locally in a shell loop. On Linux or macOS, use: for f in *.rm; do ffmpeg -i "$f" -vn -c:a pcm_s16be "${f%.rm}.au"; done. On Windows (PowerShell), use: Get-ChildItem *.rm | ForEach-Object { ffmpeg -i $_.FullName -vn -c:a pcm_s16be ($_.BaseName + '.au') }. This is especially useful for large collections of archived RealMedia content or files exceeding 1GB.
The -vn flag tells FFmpeg to ignore and discard the video stream from the RealMedia file entirely. Since AU is a pure audio container with no support for video, this flag is necessary to produce a valid output. If you removed -vn, FFmpeg would still produce an AU file because the output container enforces audio-only, but it could generate a warning or error related to the unhandled video stream, and the behavior may vary between FFmpeg versions. Keeping -vn in the command is explicit best practice for any audio-only extraction workflow.
Technical Notes
The Sun AU format's pcm_s16be codec stores audio as 16-bit signed integers in big-endian byte order, which means the output file size will be determined by: sample rate × channels × 2 bytes × duration in seconds. A typical 3-minute mono RealMedia file that was originally a small streaming-optimized AAC stream at 128k might expand to 30MB or more as uncompressed AU. The AU container does not support multiple audio tracks, subtitles, or chapters — none of which are concerns since this conversion strips everything down to a single audio stream. RealMedia files from the streaming era frequently used low sample rates (22050 Hz or even 11025 Hz) and mono audio to minimize bandwidth; FFmpeg will preserve whatever sample rate and channel layout is present in the source, which may result in AU files with lower fidelity than modern audio formats simply due to the original encoding constraints. There are no special flags or container-specific workarounds needed for this conversion — both RM and AU are well-supported in FFmpeg's format layer, and the command is clean and portable across FFmpeg versions.