Extract Audio from HEVC to AU — Free Online Tool
Extract audio from HEVC/H.265 video files and save it as a Sun AU file encoded with 16-bit big-endian PCM. This tool strips the video stream entirely and writes raw, uncompressed audio into the classic Unix AU container — useful for legacy systems, audio processing pipelines, or environments that expect the .au format.
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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
HEVC (H.265) video files typically carry an audio stream encoded in a format like AAC or AC-3 alongside the compressed video. This tool discards the video stream entirely (no video decoding occurs) and transcodes the audio into 16-bit signed big-endian PCM, which is the default codec for the Sun AU format. Because AU does not support compressed audio codecs like AAC natively in most implementations, the audio must be decoded from its original codec and re-encoded as raw PCM — this means the output is uncompressed and lossless in terms of amplitude resolution, but if the source audio was already lossy (e.g., AAC), that prior generation loss is baked in. The resulting .au file uses a simple 24-byte header followed by raw PCM sample data, making it trivially readable by virtually any audio processing library.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg multimedia processing tool. In the browser-based version of this tool, this runs via FFmpeg.wasm compiled to WebAssembly — no local FFmpeg installation is required and no files leave your device. |
-i input.hevc
|
Specifies the input file — an HEVC/H.265 encoded video file. FFmpeg will demux this container to access both the H.265 video stream and the embedded audio stream (commonly AAC or AC-3) separately. |
-vn
|
Disables all video output streams, telling FFmpeg to ignore the H.265 video track entirely. Since the goal is audio extraction, this prevents any video processing or inclusion in the output AU file, which is an audio-only format anyway. |
-c:a pcm_s16be
|
Encodes the output audio as 16-bit signed big-endian PCM, the default and most compatible codec for the Sun AU container format. The source audio (e.g., AAC from the HEVC file) is fully decoded and re-encoded into this uncompressed format, producing raw sample data in the byte order native to the original Sun SPARC architecture. |
output.au
|
Specifies the output filename with the .au extension, which tells FFmpeg to write a Sun AU container. FFmpeg uses the file extension to determine the output format, wrapping the pcm_s16be audio data in the AU format's 24-byte header structure. |
Common Use Cases
- Feeding extracted audio into Unix-based audio analysis tools or signal processing pipelines that natively read the .au format without requiring a decoder library
- Archiving the audio track from H.265 encoded video into an uncompressed format for editing in legacy audio workstations or software that predates compressed audio support
- Extracting a raw PCM audio stream from an HEVC surveillance or broadcast recording for forensic analysis or transcript generation
- Providing audio in the .au format to Sun/Oracle Java applications, which have long had built-in support for the AU container via the javax.sound API
- Stripping audio from an H.265 video to produce a headerless-ready PCM file for embedding into custom streaming or hardware audio systems that expect big-endian 16-bit samples
- Converting HEVC video audio tracks for use in older Unix workstations or academic computing environments where .au remains a standard interchange format
Frequently Asked Questions
The conversion to 16-bit PCM in the AU container is itself lossless in terms of bit depth — PCM captures audio samples directly without compression. However, if the original HEVC file's audio track was encoded in a lossy format like AAC or AC-3, that quality loss already occurred during the original encoding and cannot be recovered. The PCM output is an exact digital representation of what the lossy decoder produced, so no additional degradation is introduced by this specific conversion step.
HEVC is an extremely efficient video codec, and the audio inside an HEVC container is typically stored in a compressed format like AAC, which is also highly space-efficient. The AU format with pcm_s16be stores audio as raw, uncompressed 16-bit samples — for stereo audio at 44.1 kHz, that is roughly 10 MB per minute. Since no compression is applied to the audio in this output format, file sizes are significantly larger than the compressed source audio, and vastly larger than the original video file which also benefited from H.265 video compression.
The Sun AU format officially supports several PCM variants (signed 8-bit, unsigned 8-bit, 16-bit big-endian, 32-bit), as well as G.711 compressed formats like A-law and mu-law. The default used here is pcm_s16be — 16-bit signed big-endian PCM — because it offers the best balance of audio fidelity and broad compatibility across Unix tools and Java's sound API. Big-endian byte ordering reflects the Sun SPARC architecture origins of the format.
Yes. The FFmpeg command can be modified by changing the -c:a flag to a different PCM codec supported by the AU container. For mu-law encoding use -c:a pcm_mulaw, and for A-law use -c:a pcm_alaw. Both are lossy 8-bit companding formats historically used in telephony, and they reduce file size significantly compared to pcm_s16be but at the cost of dynamic range. The full command would look like: ffmpeg -i input.hevc -vn -c:a pcm_mulaw output.au
No. The Sun AU format has an extremely minimal header — just 24 bytes covering magic number, data offset, data size, encoding type, sample rate, and channel count. It has no standardized fields for metadata like title, artist, or album. Any metadata embedded in the HEVC container will be silently dropped during this conversion, which is an inherent limitation of the AU format rather than a tool restriction.
The exact command displayed on this page — ffmpeg -i input.hevc -vn -c:a pcm_s16be output.au — runs identically in a local FFmpeg installation with no modifications needed. Install FFmpeg for your operating system from ffmpeg.org, replace input.hevc with your actual file path, and run it in a terminal. For batch processing multiple HEVC files on Linux or macOS, you can use: for f in *.hevc; do ffmpeg -i "$f" -vn -c:a pcm_s16be "${f%.hevc}.au"; done
Technical Notes
The Sun AU format is one of the oldest structured audio containers in computing, originating with Sun Microsystems' Unix workstations in the 1980s. Its simplicity — a minimal fixed header followed by contiguous sample data — makes it trivially parseable but also severely limits its capabilities by modern standards. Notably, the AU format does not support multiple audio channels beyond what the sample rate and channel count fields encode, has no chunk-based extensibility, and lacks any container-level metadata support. When extracting from HEVC, FFmpeg must fully decode the source audio (typically AAC) before re-encoding to PCM, so this is a transcoding operation — not a remux. The output sample rate and channel count will mirror the source audio stream unless explicitly overridden with -ar and -ac flags. One practical caveat: if the HEVC source contains multiple audio tracks (e.g., a stereo and a 5.1 surround stream), FFmpeg will select only the default audio stream; use -map 0:a:1 to select a specific track. The big-endian byte order of pcm_s16be is natively understood by Java's javax.sound.sampled API, making .au files a convenient interchange format for Java-based audio applications without any third-party library dependency.