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Satori Video SDK for C++: Message formats

All Video SDK documentation

Table of contents

Overview

Video bots use the Satori publish-subscribe platform for communication, so input and output take the form of JSON messages:

  • To send analysis and debug output, you publish a message with the video API function bot_message().
  • You receive configuration input in your command processing callback. You can also publish messages from this function.
  • The SDK provides metrics to a push server that you can link to your own Prometheus site.
  • The SDK ingests video stream and video meta-data messages.

You can use any JSON content you want to publish analysis and debug messages from your bot. You can also use any format you want to publish configuration messages to the control channel.

JSON fields added by the SDK

The SDK adds two fields to messages you publish using bot_message() or return from your command processing function:

  • "from": "<bot_id>": An identifier for the bot that you specify on the bot program command line with the --id parameter. If you don't specify the parameter, the SDK doesn't add this field.
  • "i": [frame1,frame2]: Frame identifier, defined by the SDK API struct frame_id. The field has two 64-bit integers containing frame numbers frame1 and frame2. If frame1==frame2, the id specifies a single frame; otherwise, it specifies a range of frames from frame1 to frame2, inclusive. The default value is frame{[0,0]}, which the SDK interprets as the current frame.

Notes:

  • bot_id: The SDK inserts the exact value you specify on the command line.
  • frame_id: When the SDK invokes process_image(), it passes in the current frame as an image_frame struct. This struct has a frame_id member that contains the id of the frame.

Analysis messages

To publish an analysis message containing the results of your image processing, call bot_message() with the kind parameter set to the SDK API enum constant bot_message_kind::ANALYSIS.

Debug messages

To publish a debug message, call bot_message() with the kind parameter set to the SDK API enum constant bot_message_kind::DEBUG.

Configuration messages

The SDK passes messages it receives in the control channel to the command processing callback function you define, using the parameter message. This parameter is specified as a JSON object.

The following JSON object is an example of a configuration used to set the feature size in a motion detector bot:

{
    "params": {
      "featureSize" : 7.0
    }
}

This message provides a threshold value for detecting objects.

When you receive updated configurations from the control channel, move the values to the instance_data member of bot_context to make them available to your image processing callback function.