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Overview

The USB_STREAM class is the main C++ wrapper for the ESP32 USB Stream library. It provides a high-level interface for managing USB video (UVC) and audio (UAC) streaming from connected USB devices.

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Class Definition

class USB_STREAM {
  // Public interface
};

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Constructor

Creates a new USB_STREAM object. 
USB_STREAM();

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Example

#include "USB_STREAM.h"

USB_STREAM usb;

void setup() {
  // Constructor is called automatically when object is created
}

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Destructor

Destroys the USB_STREAM object and cleans up resources. 
~USB_STREAM();
The destructor is called automatically when the object goes out of scope. It ensures proper cleanup of internal resources.

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Public Member Variables

The class exposes several public member variables for storing user-defined callback functions and arguments:

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Callback Storage

void *_user_mic_frame_cb_arg
Storage for microphone frame callback argument. 
void *_user_frame_cb_arg
Storage for video frame callback argument. 
uvc_frame_callback_t _user_frame_cb
User-defined callback function for handling UVC video frames. 
mic_callback_t _user_mic_frame_cb
User-defined callback function for handling microphone audio frames.

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State Callback Type

typedef void (*StateChangeCallback)(usb_stream_state_t event, void *arg);
Callback function type for USB device connection state changes.
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event
usb_stream_state_t
Connection state event:
  • STREAM_CONNECTED (0): Device connected
  • STREAM_DISCONNECTED: Device disconnected
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arg
void*
User-defined argument passed during callback registration

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Private Member Variables

The class maintains internal state for video and audio configurations: 
uint16_t _frame_width;           // Video frame width
uint16_t _frame_height;          // Video frame height
uint32_t _frame_interval;        // Video frame interval
uint8_t _spk_ch_num;            // Speaker channel numbers
uint16_t _spk_bit_resolution;   // Speaker bit resolution
uint32_t _spk_samples_frequency; // Speaker sample frequency
uint32_t _spk_buf_size;         // Speaker buffer size
uint8_t _mic_ch_num;            // Microphone channel numbers
uint16_t _mic_bit_resolution;   // Microphone bit resolution
uint32_t _mic_samples_frequency; // Microphone sample frequency
uint32_t _mic_buf_size;         // Microphone buffer size
These private variables are managed internally by the class methods. Users should not access them directly.

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State Management

The USB_STREAM class manages the lifecycle of USB streaming through state transitions:
  1. Initial State: Object created but not configured
  2. Configured State: Video/audio parameters set via configuration methods
  3. Running State: Streaming active after calling start()
  4. Stopped State: Streaming stopped, resources freed
Always call stop() before destroying the USB_STREAM object to ensure proper resource cleanup.

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Thread Safety

Callback functions are executed in the context of internal FreeRTOS tasks. Keep callback execution time minimal and avoid blocking operations.

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