WAV MIME Type

What does audio/x-wav mean?

The audio/x-wav media type identifies a WAVE audio file, commonly called a WAV file after its .wav extension. WAVE is a chunk-based container developed by Microsoft and IBM from the Resource Interchange File Format, or RIFF. It usually carries uncompressed linear PCM audio, but the container can also hold ADPCM, mu-law, A-law, MP3, and many other encodings.¹²

That distinction matters: WAV is a container, not a promise of uncompressed audio. Two .wav files can use different sample formats or codecs, and a program that opens ordinary PCM WAV may reject a less common WAVE encoding.

audio/x-wav is a long-established but unregistered identifier. It does not appear in the current IANA media type registry. Other values seen in practice include audio/wav, audio/wave, audio/x-pn-wav, and audio/vnd.wave.³⁴ RFC 2361 defined audio/vnd.wave with a required codec parameter for referring to Microsoft's WAVE codec registry, but the RFC is Informational and the type is not listed in today's IANA media type registry.⁴

How to identify a WAV file

A conventional WAV file is a RIFF file whose form type is WAVE:

Checking only the leading RIFF bytes is not sufficient because AVI and other formats also use RIFF. A detector should confirm WAVE at bytes 8 through 11. A normal WAVE file also contains a fmt chunk describing the audio format and a data chunk carrying the audio payload. Microsoft documents WAVEFORMATEX and WAVEFORMATEXTENSIBLE structures for describing channel count, sample rate, block alignment, bit depth, and codec-specific information.⁵⁶

The usual filename extension is .wav. An extension or media type cannot reveal the codec inside, so inspect the fmt chunk when interoperability matters. Tools such as ffprobe can report the actual codec, sample rate, sample format, and channel layout without changing the file.

WAV history and media type aliases

Microsoft and IBM first released the WAVE format in 1991 as an audio form built on RIFF.¹ Its simple chunk structure and close relationship with Windows multimedia made it a durable interchange format for recording, editing, sound effects, scientific audio, and application assets.

The format also grew beyond its common stereo PCM profile. WAVEFORMATEXTENSIBLE can describe multichannel layouts and more precise sample representations. The European Broadcasting Union's Broadcast Wave Format adds a bext chunk for production metadata while remaining based on RIFF/WAVE.⁷ RF64 is a related extension that replaces 32-bit size limits with 64-bit values for files larger than 4 GB and for demanding multichannel workflows.⁸

The media type history is less tidy. The x- prefix once signaled an experimental or private name. Current IETF guidance discourages creating new X- names because widely deployed experimental names tend to become permanent compatibility burdens.⁹ Existing systems still use audio/x-wav, so changing a header without checking the recipient can be less interoperable than recognizing several aliases.

How large is uncompressed WAV audio?

For PCM audio, payload size is approximately:

sample rate x bit depth / 8 x channel count x duration

One minute of stereo 44.1 kHz, 16-bit PCM uses about 10.6 MB before chunk overhead. One minute of stereo 96 kHz, 24-bit PCM uses about 34.6 MB. Doubling the sample rate, bit depth, channel count, or duration roughly doubles the audio payload.

This predictable size makes PCM WAV fast to seek and inexpensive to decode, which is useful in editors and production tools. It is inefficient for distribution, however. FLAC can reduce PCM storage without changing the decoded samples, while AAC, MP3, and Opus make much smaller delivery files by discarding information.

How to open an audio/x-wav file

Current mainstream browsers play common LPCM WAVE audio through the HTML audio element. Browser support is much less predictable for the many other codecs that can appear inside the same container. MDN lists LPCM as the broadly supported WAVE codec and warns that support for other WAVE encodings is sparse.¹

For editing and conversion:

• Audacity imports and exports WAV, including common signed PCM and floating-point choices.¹⁰
• Adobe Audition opens uncompressed WAV files and most common compressed variants, including files with as many as 32 channels.¹¹
• FFmpeg can inspect, decode, and encode WAVE files, making it useful for batch conversion and unusual codecs.¹²

If a .wav file will not open, verify its header and codec instead of renaming it. A truncated data chunk, an incorrect RIFF length, or an unsupported codec can all produce a file that looks like WAV by extension but fails during decoding.

Support in Poly

Poly has an explicit audio/x-wav type and maps .wav filenames to it. The audio indexer loads recognized files through its decoder, extracts duration and available tags, uses embedded cover art when present, and transcribes spoken audio to WebVTT. Transcript segments become full-text search results and can seek the player to the matching moment.

Poly also creates timestamped audio-similarity embeddings in 15-second segments. Clips shorter than eight seconds are not embedded for audio similarity. A useful transcript depends on intelligible speech, so music, ambience, and sound effects may still be searchable by filename, metadata, and audio similarity even when transcript search adds little.

The in-app audio player receives the original file rather than a standardized playback transcode. It also attempts to calculate a waveform from the cached file. Common PCM WAV works well, but an unusual WAVE codec can prevent metadata extraction, waveform generation, transcription, similarity indexing, or browser playback if Poly's decoder or the browser cannot decode it.

The Poly agent has two content paths for WAV. It can read the stored transcript, and its multimodal backend explicitly accepts WAV audio by sending the original as audio/wav. Direct audio has an eight-hour limit in the current backend. For speech recordings, the transcript is generally the best searchable representation; for non-speech audio, direct analysis and similarity search are more relevant.

Converting WAV to a smaller or more portable format

Choose the output based on the next use:

• FLAC for lossless storage of PCM audio with smaller files. Some WAVE-specific chunks and production metadata may not have equivalent FLAC fields.
• AAC, MP3, or Opus for compact playback and distribution. These are lossy at ordinary settings, so keep the WAV or another lossless master.
• AIFF for an uncompressed interchange file when an Apple-oriented production workflow expects it.
• Broadcast WAVE or RF64 for professional metadata, multichannel delivery, or recordings that exceed classic RIFF size limits.⁷⁸

For a lossless FLAC working copy:

ffmpeg -i input.wav -c:a flac output.flac

For a conventional 16-bit PCM WAV intended for broad compatibility:

ffmpeg -i input.wav -c:a pcm_s16le output.wav

The second command may change bit depth or discard an unsupported encoding. Check the source first, and preserve the original when metadata, provenance, or exact sample representation matters.

Is WAV the same as WAVE?

Yes in ordinary usage. WAVE is the format's name and WAV comes from the .wav extension. Neither term means that the audio must be PCM, although uncompressed PCM is by far the most interoperable profile.

WAV is not the same container as AIFF or FLAC. AIFF uses the related IFF chunk model and traditionally stores multibyte PCM in big-endian order. FLAC is a lossless compressed audio format with its own stream structure. Renaming extensions does not convert between them.