What does it cost to convert AVI to MP3?

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

How large can the AVI 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 / AVI to MP3

Convert AVI to MP3

To convert AVI to MP3, send one POST to /v1/audio-convert with the AVI source and "to": "mp3" in the body. "mp3" is the schema default of "to", so the field may also be left out. 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 AVI to MP3 run of audio-convert.

Request

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

{
  "url": "https://grist.tools/samples/av/pair-clip.avi",
  "to": "mp3"
}

Response

200 OK
payment-response: <base64 settlement receipt>

{
  "source_url": "https://grist.tools/samples/av/pair-clip.avi",
  "bytes": 76302,
  "source_container": "avi",
  "format": "mp3",
  "bitrate_kbps": null,
  "sample_rate": null,
  "audio_bytes": 4196,
  "audio_base64": "SUQzBAAAAAAACgAAAAAAAAAAAAD/4xjEAAxoAub5QBAAh1QgCdy3AiAECgDB/D8Q..."
}

Source file: av/pair-clip.avi, 74.5 KB (76,302 bytes). 4 s AVI file made by ffmpeg: a 64x36 PNG video stream at 1 fps (a slate field with a small amber square moving right) and a mono 8 kHz 16-bit PCM audio track of two 500 Hz triangle beeps; no subtitle stream. The recorded run returned 4.1 KB (4,196 bytes) of MP3, 5% of the source size, with the source read as the avi container. Decoded, the MP3 in audio_base64 opens with 49 44 33 04 00 00 00 00 00 0A 00 00. Recorded with ffmpeg 8.1.2.

In the sample itself, the avih main header sets 1,000,000 microseconds per frame, 4 frames, 2 streams and a 64 by 36 frame; the stream headers are vids with handler MPNG, rate 1 over scale 1 and auds, rate 8,000 over scale 1, format tag 0x0001 at 8,000 Hz and 16 bits; an idx1 chunk indexes the frames at the end of the file. In the returned MP3: it opens with an ID3v2.4 tag with 10 bytes of body, then an MPEG 2.5 Layer III frame header at byte 20: 8 kbps, 8,000 Hz, mono.

03Format notes

AVI as a source

AVI is a RIFF container whose form type at byte eight is the four characters AVI followed by a space. Grist checks that form type, not the extension, before ffmpeg sees the file. Three of the conversion services on these pages accept it. audio-convert reads the first audio stream and ignores video; video-thumbnail seeks at the demuxer and decodes exactly one frame with audio disabled; subtitle-extract maps a subtitle stream by its zero-based index. That last route has a practical gap: ffmpeg's AVI muxer writes no text subtitle stream, only DivX XSUB bitmaps, so no real AVI with text captions could be produced for an example, and the AVI subtitle pages carry none. An AVI whose subtitle index matches nothing is refused rather than answered with an empty result. Each response reports the sniffed container as avi alongside the size of the fetched file.

MP3 as a target

MP3 is the default value of audio-convert's to field, encoded with the pinned libmp3lame codec. The mp3 muxer needs no seeking, so output streams straight to a pipe instead of a temporary file. bitrate_kbps applies to this lossy destination; when it is omitted, no audio bitrate argument is passed, the encoder's own default applies, and the response reports the bitrate as null. An optional sample_rate selects from the closed set, otherwise ffmpeg normally follows the source. Only the first audio stream is encoded, and video, chapters and metadata are left out, with bit-exact flags keeping the bytes reproducible for the pinned ffmpeg. Even with source metadata removed, each recorded MP3 output still begins with an ID3v2 tag written by the muxer. Inputs whose duration exceeds the service limit are refused before encoding.

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 AVI to MP3?: $0.003 per call, paid in USDC on Base via x402.
How large can the AVI 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.