What does it cost to convert WAV to AAC?

$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 AAC

Convert WAV to AAC

To convert WAV to AAC, send one POST to /v1/audio-convert with the WAV source and "to": "aac" in the body. Left out, "to" falls back to its default "mp3", so a AAC 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 AAC 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": "aac"
}

Response

200 OK
payment-response: <base64 settlement receipt>

{
  "source_url": "https://grist.tools/samples/av/waveform-beeps.wav",
  "bytes": 32044,
  "source_container": "wav",
  "format": "aac",
  "bitrate_kbps": null,
  "sample_rate": null,
  "audio_bytes": 5268,
  "audio_base64": "//FsQEcf/AEIVCwkSCWOhseh2GBMWgoSxP/FVWquNyXXqT27fHGt/by8JON5JU//..."
}

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 5.1 KB (5,268 bytes) of AAC, 16% of the source size, with the source read as the wav container. Decoded, the AAC in audio_base64 opens with FF F1 6C 40 47 1F FC 01 08 54 2C 24. 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 AAC: it opens with an ADTS frame header carrying no CRC: MPEG-4 AAC LC, 8,000 Hz, 1 channel, a first frame of 568 bytes, and buffer fullness 0x7FF, the value that marks a variable bitrate stream.

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.

AAC as a target

AAC output is a raw ADTS stream: ffmpeg's aac encoder writes through the adts muxer, and no MP4 container is built around it. Each ADTS frame carries its own header, and the stream is written straight to a pipe without a seekable file. The bitrate_kbps setting applies, but AAC has its own lower ceiling, because it is the slowest encoder of the set and that ceiling keeps a maximum-length input inside the encode deadline. Only the first audio stream is encoded; video, metadata and chapters are dropped, and bit-exact flags keep output reproducible for the pinned ffmpeg. sample_rate is optional, otherwise ffmpeg normally keeps the source rate. AAC is a destination only: a raw ADTS file would pass the MPEG frame-sync sniff, yet nothing proves ffmpeg would receive the right demuxer, so it is not accepted as a source.

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 AAC?: $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.