Extract Audio from WTV to AU — Free Online Tool
Extract audio from Windows Media Center TV recordings (.wtv) and convert it to Sun AU format using PCM signed 16-bit big-endian encoding. This tool strips the video stream entirely and outputs uncompressed PCM audio — ideal for Unix-based workflows or applications that require the classic .au container.
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FFmpeg Command
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Estimated output:
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DownloadHow It Works
WTV files recorded by Windows Vista Media Center typically contain an H.264 video stream and AAC or MP3 audio. This conversion discards the video stream entirely using the -vn flag and decodes the compressed audio (AAC or MP3) from the WTV container, then re-encodes it as PCM signed 16-bit big-endian (pcm_s16be) — the default and most compatible codec for the Sun AU format. Because the audio goes from a lossy compressed codec (AAC/MP3) to an uncompressed PCM representation, no further lossy compression is added, but the original compression artifacts from the WTV recording are preserved. The resulting .au file has a simple fixed header with no support for multiple tracks, chapters, or metadata beyond basic encoding parameters.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg multimedia processing engine, which runs here entirely in your browser via WebAssembly (FFmpeg.wasm) — no data leaves your machine. |
-i input.wtv
|
Specifies the input file, a Windows Media Center TV recording in the WTV container, which typically holds H.264 video and AAC or MP3 audio captured from a digital broadcast tuner. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore the H.264 (or MJPEG) video stream in the WTV file. Since AU is an audio-only format, this flag is required — without it FFmpeg would attempt to include a video stream that AU cannot contain. |
-c:a pcm_s16be
|
Sets the audio codec to PCM signed 16-bit big-endian, which is the standard and most widely compatible encoding for the Sun AU container. This decodes the compressed AAC or MP3 audio from the WTV file into uncompressed PCM samples stored in big-endian byte order as required by the AU format specification. |
output.au
|
Defines the output filename and, through the .au extension, signals FFmpeg to use the Sun AU container format — a simple fixed-header audio container developed by Sun Microsystems and commonly used on Unix systems and in Java applications. |
Common Use Cases
- Extracting the audio commentary or dialogue from a recorded TV broadcast for transcription or archiving on a Unix/Linux system
- Feeding recorded television audio into legacy Unix audio tools or scientific software that natively reads the Sun AU format
- Converting a Windows Media Center DVR recording to an uncompressed PCM audio file for lossless waveform analysis or editing
- Preparing TV broadcast audio in AU format for use with older Java applications, which have built-in support for the .au container via the Java Sound API
- Extracting a specific audio track from a multi-track WTV recording (e.g., an alternate language track) to a standalone uncompressed AU file
- Archiving the audio portion of a recorded TV program in a simple, well-documented PCM format that will remain readable without proprietary codecs
Frequently Asked Questions
The WTV file's audio is already lossy-compressed as AAC or MP3, so some quality was lost at the point of recording. Converting to AU with pcm_s16be decodes that compressed audio to uncompressed PCM, which means no additional lossy encoding is applied — you get the best possible fidelity from what the WTV file already contains. However, you cannot recover quality that was lost during the original broadcast recording, so the AU file will reflect any artifacts already present in the WTV source.
The AU format stores audio as uncompressed PCM (specifically 16-bit signed big-endian samples in this conversion), whereas the WTV file stores audio as AAC or MP3, which are highly compressed codecs. Uncompressed audio requires roughly 10 MB per minute per channel at 44.1 kHz, compared to just 1 MB per minute for 128 kbps AAC. This size increase is expected and is the tradeoff for having raw, uncompressed audio that any PCM-capable tool can read without a decoder.
No. The Sun AU format has an extremely minimal header that stores only technical audio parameters (sample rate, bit depth, channel count, and encoding type). It has no support for metadata fields such as title, artist, broadcast date, or episode information. Any DVR metadata embedded in the WTV file — including program guide data — will be lost in the conversion. If preserving metadata matters, consider extracting to a format like FLAC or MP3 instead.
Yes, but you need to modify the FFmpeg command manually. WTV files can contain multiple audio tracks (for example, stereo and Dolby Digital, or multiple language tracks). By default, FFmpeg selects the best audio stream automatically. To select a specific track, add -map 0:a:1 before the output filename to pick the second audio track (index 1), or -map 0:a:2 for the third, and so on. Note that AU only supports a single audio stream, so you must select one track — you cannot merge multiple tracks into a single AU file.
Yes. The Sun AU format supports several PCM variants beyond the default pcm_s16be, including pcm_s8 (8-bit signed), pcm_u8 (8-bit unsigned), pcm_alaw (G.711 A-law), and pcm_mulaw (G.711 mu-law). To use a different codec, replace pcm_s16be in the command with your preferred codec, for example: ffmpeg -i input.wtv -vn -c:a pcm_mulaw output.au. The mu-law and A-law options are lossy telephony codecs that significantly reduce file size but at the cost of audio quality, while the PCM options are lossless representations.
On Linux or macOS, you can loop over all WTV files in a directory with: for f in *.wtv; do ffmpeg -i "$f" -vn -c:a pcm_s16be "${f%.wtv}.au"; done. On Windows Command Prompt, use: for %f in (*.wtv) do ffmpeg -i "%f" -vn -c:a pcm_s16be "%~nf.au". This processes each file sequentially, stripping the video and converting the audio to pcm_s16be AU. Keep in mind that uncompressed AU files can be large, so make sure you have sufficient disk space before batch processing a large DVR library.
Technical Notes
WTV is a container format tied to the Windows Media Center DVR ecosystem and uses a variant of the Advanced Systems Format (ASF) internally. Its audio streams are most commonly AAC-LC or MP3, encoded at the time of broadcast capture. The Sun AU format, by contrast, is one of the oldest and simplest audio containers still in use, developed by Sun Microsystems and natively supported in early Java runtimes and Unix audio subsystems. The pcm_s16be codec used here stores samples as 16-bit integers in big-endian byte order — this byte order is significant on little-endian systems (such as x86) where byte-swapping must occur during playback, though all conformant AU players handle this transparently. AU files do not support metadata, chapters, multiple audio tracks, or subtitle streams, so anything beyond the primary audio signal in the WTV file is discarded. Because the conversion decodes compressed audio to PCM, CPU usage and processing time are moderate even for long recordings. For very long TV recordings (e.g., multi-hour sports events), the resulting AU file size can be substantial — a two-hour stereo recording at 44.1 kHz will produce an AU file of approximately 1.1 GB.