What does it cost to convert FLAC to WAV?

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

How large can the FLAC 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 / FLAC to WAV

Convert FLAC to WAV

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

Request

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

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

Response

200 OK
payment-response: <base64 settlement receipt>

{
  "source_url": "https://grist.tools/samples/av/convert-beeps.flac",
  "bytes": 32086,
  "source_container": "flac",
  "format": "wav",
  "bitrate_kbps": null,
  "sample_rate": null,
  "audio_bytes": 32044,
  "audio_base64": "UklGRiR9AABXQVZFZm10IBAAAAABAAEAQB8AAIA+AAACABAAZGF0YQB9AAAA4ADo..."
}

Source file: av/convert-beeps.flac, 31.3 KB (32,086 bytes). Two-second mono 16-bit FLAC at 8 kHz holding the same three rising 500 Hz beeps as waveform-beeps.wav, written with uncompressed verbatim subframes by a TypeScript generator. The recorded run returned 31.3 KB (32,044 bytes) of WAV, 100% of the source size, with the source read as the flac container. Decoded, the WAV in audio_base64 opens with 52 49 46 46 24 7D 00 00 57 41 56 45 (ASCII RIFF and WAVE). Recorded with ffmpeg 8.1.2.

In the sample itself: its 34-byte STREAMINFO block, in its own field order, declares blocks of 4,096 samples, no largest frame size, 8,000 Hz, 1 channel, 16 bits per sample and 16,000 samples in total. In the returned WAV: 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.

03Format notes

FLAC as a source

A native FLAC stream begins with the four ASCII characters fLaC, and that marker is what Grist sniffs. FLAC compresses audio losslessly, so decoding restores the exact samples that were encoded. audio-convert is the only service that reads the format directly, and its own canonical example decodes a FLAC file to a bit-exact PCM WAV. FLAC audio can also sit inside other containers as a stream, but such files are recognised by their container signature and reported under that container, not as flac. Before encoding, the stream length is measured and checked against the service's duration limit. Like every audio-convert source, only the first audio stream is used, metadata and chapter information are stripped, and the pinned ffmpeg with bit-exact flags makes the result reproducible. A lossy destination discards information the FLAC still held.

WAV as a target

WAV output is written with the pinned pcm_s16le codec, so every result holds signed little-endian PCM regardless of the source encoding. The WAV muxer fills in its RIFF chunk sizes when the file closes, so Grist points ffmpeg at a seekable temporary file inside the per-call directory and reads it back, rather than streaming to a pipe. A bitrate_kbps value is rejected for this lossless destination instead of being ignored. The optional sample_rate must come from the service's closed set; left out, ffmpeg chooses, normally keeping the source rate. Only the first audio stream is mapped, with video, metadata and chapters removed, and bit-exact flags make the bytes reproducible for the pinned ffmpeg. PCM from a lossy source contains the decoded samples at full size, without restoring detail the earlier codec discarded.

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 FLAC to WAV?: $0.003 per call, paid in USDC on Base via x402.
How large can the FLAC 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.