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When you submit a task to the upload and extend audio API, you can use the callBackUrl parameter to set a callback URL. When the task is completed, the system will automatically push the results to your specified address.

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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.

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Callback Timing

The system will send callback notifications in the following situations:
  • Text generation completed (text stage)
  • First extended audio track generated (first stage)
  • All extended audio tracks generated (complete stage)
  • Audio extension task failed
  • Error occurred during task processing

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Callback Method

  • HTTP Method: POST
  • Content Type: application/json
  • Timeout: 15 seconds

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Callback Request Format

When a task is completed, the system will send a POST request to your callBackUrl in the following format: 
{
  "code": 200,
  "msg": "Text generation completed successfully.",
  "data": {
    "callbackType": "text",
    "task_id": "2fac****9f72",
    "data": []
  }
}

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Status Code Description

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code
integer
required
Callback status code indicating task processing result:
Status CodeDescription
200Success - Extension completed
400Bad Request - Parameter error or invalid audio file
401Unauthorized - Invalid API key
413Content Too Long - Audio file too large or duration exceeds limit
429Insufficient Credits - Account credit balance insufficient
500Server Error - Please retry later
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msg
string
required
Status message providing detailed status description
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data.callbackType
string
required
Callback type indicating current callback stage:
  • text: Text generation complete
  • first: First extension complete
  • complete: All extensions complete
  • failed: Task failed
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data.task_id
string
required
Task ID, consistent with the taskId returned when you submitted the task
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data.data
array
Extension result information, returned on success
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data.data[].id
string
Unique audio identifier (audioId)
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data.data[].audio_url
string
Extended audio file download link
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data.data[].source_audio_url
string
Original audio file download link
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data.data[].stream_audio_url
string
Streaming audio playback link
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data.data[].image_url
string
Music cover image link
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data.data[].prompt
string
Prompt/lyrics used for extension
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data.data[].model_name
string
AI model name used
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data.data[].title
string
Music title
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data.data[].tags
string
Music style tags
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data.data[].createTime
string
Creation time
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data.data[].duration
number
Extended audio duration (seconds)

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Best Practices

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Callback URL Configuration Recommendations

  1. Use HTTPS: Ensure callback URLs use HTTPS protocol for secure data transmission
  2. Verify Source: Validate the legitimacy of request sources in callback processing
  3. Idempotent Processing: The same taskId may receive multiple callbacks, ensure processing logic is idempotent
  4. Quick Response: Callback processing should return 200 status code quickly to avoid timeout
  5. Asynchronous Processing: Complex business logic should be processed asynchronously to avoid blocking callback response
  6. Stage-based Processing: Perform appropriate business processing based on different callback stages
  7. Audio Comparison: Compare audio duration and quality changes before and after extension
  8. Upload Validation: Ensure uploaded audio file quality and integrity

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Important Reminders

  • Callback URL must be a publicly accessible address
  • Server must respond within 15 seconds, otherwise considered timeout
  • After 3 consecutive retry failures, the system will stop sending callbacks
  • Please ensure the stability of callback processing logic to avoid callback failures due to exceptions
  • Extended audio URLs may have time limits, recommend downloading and saving promptly
  • Uploaded audio files must not exceed 2 minutes, ensure compliance with limits
  • Extension function will extend audio length while maintaining original style
  • Music extension has three stages, each stage will trigger callback notifications

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Troubleshooting

If you don’t receive callback notifications, please check the following:
  • Confirm that the callback URL is accessible from the public internet
  • Check firewall settings to ensure inbound requests are not blocked
  • Verify that domain name resolution is correct
  • Ensure the server returns HTTP 200 status code within 15 seconds
  • Check server logs for error information
  • Verify that the interface path and HTTP method are correct
  • Confirm that the upload URL is valid and accessible
  • Check the uploaded audio file format and quality
  • Verify that the audio file duration does not exceed the 2-minute limit
  • Confirm that extension parameters (continueAt, etc.) are set correctly
  • Understand the differences and processing methods of the three callback stages
  • text stage: Only indicates text generation complete, no audio data
  • first stage: First extended music complete, contains data for one track
  • complete stage: All extended music complete, contains complete music list

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Alternative Solutions

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

Poll Extension Results

Use the Get Music Generation Details interface to regularly query extension task status. Recommend querying every 30 seconds.