MIDI Generation Callbacks

System will call this callback when MIDI generation from separated audio is complete.

When you submit a MIDI generation task to the Suno API, you can use the callBackUrl parameter to set a callback URL. The system will automatically push the results to your specified address when the task is completed.

Callback Mechanism Overview

The callback mechanism eliminates the need to poll the API for task status. The system will proactively push task completion results to your server.

Webhook Security

To ensure the authenticity and integrity of callback requests, we strongly recommend implementing webhook signature verification. See our Webhook Verification Guide for detailed implementation steps.

Callback Timing

The system will send callback notifications in the following situations:

MIDI generation task completed successfully

MIDI generation task failed

Errors occurred during task processing

Callback Method

HTTP Method: POST

Content Type: application/json

Timeout Setting: 15 seconds

Callback Request Format

When the task is completed, the system will send a POST request to your callBackUrl:

Success Callback

Failure Callback

{
  "task_id": "5c79****be8e",
  "code": 200,
  "msg": "success",
  "data": {
    "state": "complete",
    "instruments": [
      {
        "name": "Drums",
        "notes": [
          {
            "pitch": 73,
            "start": "0.036458333333333336",
            "end": "0.18229166666666666",
            "velocity": 1
          },
          {
            "pitch": 61,
            "start": 0.046875,
            "end": "0.19270833333333334",
            "velocity": 1
          },
          {
            "pitch": 73,
            "start": 0.1875,
            "end": "0.4895833333333333",
            "velocity": 1
          }
        ]
      },
      {
        "name": "Electric Bass (finger)",
        "notes": [
          {
            "pitch": 44,
            "start": 7.6875,
            "end": "7.911458333333333",
            "velocity": 1
          },
          {
            "pitch": 56,
            "start": 7.6875,
            "end": "7.911458333333333",
            "velocity": 1
          },
          {
            "pitch": 51,
            "start": 7.6875,
            "end": "7.911458333333333",
            "velocity": 1
          }
        ]
      }
    ]
  }
}

Status Code Description

code (integer, required)

Callback status code indicating task processing result:

Status Code	Description
200	Success - MIDI generation completed successfully
500	Internal Error - Please try again or contact support

msg (string, required)

Status message providing detailed status description

task_id (string, required)

Task ID, consistent with the task_id returned when you submitted the task

data (object)

MIDI generation result information, returned on success

Success Response Fields

data.state (string)

Processing state. Value: complete when successful

data.instruments (array)

Array of detected instruments with their MIDI note data

Instrument Object Properties:

name (string) — Instrument name (e.g., "Drums", "Electric Bass (finger)", "Acoustic Grand Piano")

notes (array) — Array of MIDI notes for this instrument

Note Object Properties:

pitch (integer) — MIDI note number (0-127). Middle C = 60. MIDI note reference

start (number | string) — Note start time in seconds from beginning of audio

end (number | string) — Note end time in seconds from beginning of audio

velocity (number) — Note velocity/intensity (0-1 range). 1 = maximum velocity

Callback Reception Examples

Below are example codes for receiving callbacks in popular programming languages:

Node.js

Python

PHP

Best Practices

Callback URL Configuration Recommendations

Use HTTPS: Ensure callback URL uses HTTPS protocol for secure data transmission

Verify Origin: Verify the legitimacy of the request source in callback processing

Idempotent Processing: The same task_id may receive multiple callbacks, ensure processing logic is idempotent

Quick Response: Callback processing should return 200 status code quickly to avoid timeout

Asynchronous Processing: Complex business logic (like MIDI file conversion) should be processed asynchronously

Handle Missing Instruments: Not all instruments may be detected - handle empty or missing instrument arrays gracefully

Store Raw Data: Save the complete JSON response for future reference and reprocessing

Important Reminders

Callback URL must be publicly accessible

Server must respond within 15 seconds, otherwise will be considered timeout

If 3 consecutive retry attempts fail, the system will stop sending callbacks

Please ensure the stability of callback processing logic to avoid callback failures due to exceptions

MIDI data is retained for 14 days - download and save promptly if needed long-term

The number and types of instruments detected depends on audio content

Note times (start/end) may be strings or numbers - handle both types

Troubleshooting

If you are not receiving callback notifications, please check the following:

Network Connection Issues

Confirm callback URL is accessible from public internet

Check firewall settings to ensure inbound requests are not blocked

Verify domain name resolution is correct

Server Response Issues

Ensure server returns HTTP 200 status code within 15 seconds

Check server logs for error messages

Verify endpoint path and HTTP method are correct

Content Format Issues

Confirm received POST request body is in JSON format

Check if Content-Type is application/json

Verify JSON parsing is correct

Handle both string and number types for timing values

Data Processing Issues

Some instruments may have empty note arrays

Not all audio will detect all instrument types

Verify the original vocal separation used split_stem type (not separate_vocal)

Check that the source taskId is from a successfully completed separation

Alternative Solutions

If you cannot use the callback mechanism, you can also use polling:

Poll Query Results

Use the Get MIDI Generation Details endpoint to periodically query task status. We recommend querying every 10-30 seconds.

MIDI Generation Callbacks

Callback Mechanism Overview#

Callback Timing#

Callback Method#

Callback Request Format#

Status Code Description#

code (integer, required)#

msg (string, required)#

task_id (string, required)#

data (object)#

Success Response Fields#

data.state (string)#

data.instruments (array)#

Callback Reception Examples#

Best Practices#

Troubleshooting#

Alternative Solutions#

Callback Mechanism Overview

Callback Timing

Callback Method

Callback Request Format

Status Code Description

code (integer, required)

msg (string, required)

task_id (string, required)

data (object)

Success Response Fields

data.state (string)

data.instruments (array)

Callback Reception Examples

Best Practices

Troubleshooting

Alternative Solutions