What does it cost to convert WAV to Opus?

$0.003 per call, paid in USDC on Base via x402.

How large can the WAV file be?

Up to 100 MB (104,857,600 bytes), and at most 60 min (3,600 s) of media. Past a limit the call answers too_large (413).

What happens if the conversion fails?

The tool answers with a typed JSON error from the errors table. Payment is settled only after the tool has produced its result; a call that fails inside the tool is never settled.

catalogue / tools / Audio & video / WAV to Opus

Convert WAV to Opus

To convert WAV to Opus, send one POST to /v1/audio-convert with the WAV source and "to": "opus" in the body. Left out, "to" falls back to its default "mp3", so a Opus request has to send it. Each call costs $0.003 in USDC on Base via x402, with no account and no API key. The source file can be up to 100 MB and 60 min (3,600 s) long.

Endpoint: POST /v1/audio-convert
Price: $0.003 per call
Service: audio-convert
Docs: /docs/audio-convert

01Limits

Limit	Value
Largest source file	100 MB (104,857,600 bytes)
Longest input	60 min (3,600 s)
Timeout	94 s
Source formats	AIFF, AVI, FLAC, MKV, MP3, MP4, Ogg, WAV
Output formats	AAC, FLAC, MP3, Opus, WAV

02Example

A real WAV to Opus run of audio-convert.

Request

POST /v1/audio-convert
content-type: application/json
payment-signature: <base64 x402 payload>

{
  "url": "https://grist.tools/samples/av/waveform-beeps.wav",
  "to": "opus"
}

Response

200 OK
payment-response: <base64 settlement receipt>

{
  "source_url": "https://grist.tools/samples/av/waveform-beeps.wav",
  "bytes": 32044,
  "source_container": "wav",
  "format": "opus",
  "bitrate_kbps": null,
  "sample_rate": null,
  "audio_bytes": 17130,
  "audio_base64": "T2dnUwACAAAAAAAAAAAAAAAAAAAAAGS5xGoBE09wdXNIZWFkAQE4AUAfAAAAAABP..."
}

Source file: av/waveform-beeps.wav, 31.3 KB (32,044 bytes). Two-second mono 16-bit PCM WAV at 8 kHz: three 0.4 s 500 Hz triangle-wave beeps at rising level separated by silence, generated from integer arithmetic. The recorded run returned 16.7 KB (17,130 bytes) of Opus, 53% of the source size, with the source read as the wav container. Decoded, the Opus in audio_base64 opens with 4F 67 67 53 00 02 00 00 00 00 00 00 (ASCII OggS). Recorded with ffmpeg 8.1.2.

In the sample itself: The RIFF header counts 32,036 bytes after itself, and the fmt chunk, in its own field order, declares audio format 1 (integer PCM), 1 channel, 8,000 Hz, 16,000 bytes per second, a block align of 2 bytes and 16 bits per sample. The data chunk right after it holds 32,000 bytes of samples, 2 s at that rate. In the returned Opus: the first Ogg page, flagged as the beginning of the stream, has stream serial 0 and one 19-byte packet, the OpusHead: version 1, 1 channel, a pre-skip of 312 samples, an input sample rate of 8,000 Hz and channel mapping family 0.

03Format notes

WAV as a source

WAV is a RIFF file whose form type at byte eight reads WAVE, and it usually carries uncompressed PCM samples. Grist requires both markers, which keeps WebP images and AVI video, the other RIFF users, out of the audio path. Because a WAV holds audio alone, video-thumbnail and subtitle-extract refuse it as a container without a picture or caption stream, and only audio-convert accepts it. Before any sample is encoded, the length of the first audio stream is measured, first from the container header and, when that is missing or doubtful, by scanning packet timestamps; a file whose duration cannot be established is refused instead of being encoded blind. Since PCM is already decoded audio, the converter reads the samples directly rather than undoing another codec before the destination encoder runs.

Opus as a target

An Opus result is libopus-encoded audio inside an Ogg container: the ogg muxer writes it, and the recorded outputs begin with the OggS capture pattern followed by an OpusHead identification header. For that reason a returned Opus file is recognised as ogg if it is submitted again, and opus never appears as a source slug. bitrate_kbps controls the lossy encode, and an optional sample_rate may be chosen from the closed set; left out, ffmpeg normally follows the source rate. The input's duration is checked first, then the first audio stream alone is encoded, excluding video, metadata and chapters. Pinned ffmpeg and bit-exact flags make repeated calls return the same bytes. With no bitrate given the encoder's default rate applies, and for the recorded low-rate mono examples that default produced larger files than the MP3 default.

04Errors

Code	HTTP
`invalid_input`	`400`
`blocked_target`	`403`
`unreachable_target`	`424`
`upstream_timeout`	`424`
`unsupported_content_type`	`415`
`too_large`	`413`
`unprocessable`	`422`
`internal`	`500`

When each is raised, and what it means for payment: /docs/audio-convert.

05Questions

What does it cost to convert WAV to Opus?: $0.003 per call, paid in USDC on Base via x402.
How large can the WAV file be?: Up to 100 MB (104,857,600 bytes), and at most 60 min (3,600 s) of media. Past a limit the call answers too_large (413).
What happens if the conversion fails?: The tool answers with a typed JSON error from the errors table. Payment is settled only after the tool has produced its result; a call that fails inside the tool is never settled.