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Live subtitles Event Notification
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Last updated: 2025-12-03 17:56:30
Live subtitles Event Notification
Last updated: 2025-12-03 17:56:30
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This document mainly describes the callback notification fields sent to users when Tencent Cloud Streaming Service (CSS) triggers a live subtitle event.

Note

This guide assumes that you understand how to configure callbacks and receive callback notifications from CSS. For details, see How to Receive Event Notification.
Callback information is only returned when pulling subtitle streams.

Event Message Notification Protocol

Network Protocols
Request: Utilize an HTTP POST request with the body content in JSON format. The specific body content for each message type is detailed in the subsequent sections.
Response: The HTTP status code is 200. While the server disregards the specific content of the response packet, for protocol compatibility, it is recommended that the client includes a JSON payload in the response: `{"code":0}`.
Message Reliability
The Event Notification Service incorporates a retry mechanism with a total of 3 attempts. To prevent potential impact on your server performance and network bandwidth due to retries, please ensure proper response packets are returned. The conditions triggering retries are as follows:
No response packet received for an extended duration.
The HTTP status code returned is not 200.

Live subtitles Event Parameters

Event type

Event Type
Value
Live subtitles
event_type = 338

Common callback parameters

Parameter
Type
Description
t
int64
Expiration time, which is the Unix timestamp when the event notification signature expires.
The default validity period of a callback notification from Tencent Cloud is 10 minutes. If the time specified by the t value in a notification has elapsed, then this notification is considered invalid. This prevents network replay attacks.
The value of t is a decimal Unix timestamp, that is, the number of seconds that have elapsed since 00:00:00 (UTC/GMT time), January 1, 1970.
sign
string
Security signature. sign = MD5(key + t). Tencent Cloud splices the encryption key and t, generates the MD5 hash of the spliced string, and embeds it in callback messages. Your backend server can perform the same calculation when it receives a callback message. If the signature matches, it indicates the message is from Tencent Cloud.
Note:
You can set the callback key in Feature Configuration > Live Stream Callback, which is used for authentication. We recommend you set this field to ensure data security.


Callback parameters

Parameter
Type
Description
appid
int
User APPID.
stream_id
string
Live stream name.
channel_id
string
Same as the live stream name.
task_id
string
Subtitle task ID.
data
Process the results.

data

Parameter
Type
Description
subtitle_tmp_res
Subtitle text results.

subtitle_tmp_res
Parameter
Type
Description
src_txt
string
Original audio recognition text.
dst_txt
string
The translated text. If no translation is configured, this value is not returned.
start_pts
int64
src_txt corresponds to the timestamp starting point of the audio stream, in milliseconds (ms).
end_pts
int64
src_txt corresponds to the timestamp end point of the audio stream, in milliseconds (ms).
start_unix_time
int64
src_txt corresponds to the UNIX time starting point of the live broadcast.
end_unix_time
int64
src_txt corresponds to the UNIX time end point of the live broadcast.
steady_state
bool
Steady state flag: When true, it indicates that the sentence has entered a stable state and the text will no longer be revised.

Sample callback

{
  "event_type": 338,
  "stream_id": "teststream",
  "channel_id": "teststream",
  "task_id": "7735333",
  "data": {
    "subtitle_tmp_res": [
      {
        "src_txt": "Today we shall delve into the study of linear equations in one variable.",
        "start_pts": 123000,
        "end_pts": 126333,
		"stead_state": bool
      }
    ]
  },
  "sign": "ca3e25e5dc17a6f9909a9ae7281e300d",
  "t": 1754623810
}
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