I'm writing a program to control a PTZ camera connected via USB.
I can get access to target camera's unique_id, and also other infos provided by AVFoundation. But I don't know how to locate my target USB device to send a UVC ControlRequest.
There's many Cameras with same VendorID and ProductID connected at a time, so I need a more exact way to find out which device is my target.
It looks that the unique_id provided is (locationID<<32|VendorID<<16|ProductID) as hex string, but I'm not sure if I can always assume this behavior won't change.
Is there's a document declares how AVFoundation generate the unique_id for USB camera, so I can assume this convert will always work? Or is there's a way to send a PTZ control request to AVCaptureDevice?
https://stackoverflow.com/questions/40006908/usb-interface-of-an-avcapturedevice
I have seen this similar question. But I'm worrying that Exacting LocationID+VendorID+ProductID from unique_id seems like programming to implementation instead of interface. So, if there's any other better way to control my camera?
here's my example code for getting unique_id:
//
// camera_unique_id_test.mm
//
// 测试代码：使用C++获取当前系统摄像头的AVCaptureDevice unique_id
//
// 编译命令:
// clang++ -framework AVFoundation -framework CoreMedia -framework Foundation
// camera_unique_id_test.mm -o camera_unique_id_test
//
#include <iostream>
#include <string>
#include <vector>
#import <AVFoundation/AVFoundation.h>
#import <Foundation/Foundation.h>
struct CameraInfo {
std::string uniqueId;
};
std::vector<CameraInfo> getAllCameraDevices() {
std::vector<CameraInfo> cameras;
@autoreleasepool {
NSArray<AVCaptureDevice*>* devices =
[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
AVCaptureDevice* defaultDevice =
[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
// 遍历所有设备
for (AVCaptureDevice* device in devices) {
CameraInfo info;
// 获取unique_id
info.uniqueId = std::string([device.uniqueID UTF8String]);
cameras.push_back(info);
}
}
return cameras;
}
int main(int argc, char* argv[]) {
std::vector<CameraInfo> cameras = getAllCameraDevices();
for (size_t i = 0; i < cameras.size(); i++) {
const CameraInfo& camera = cameras[i];
std::cout << " 设备 " << (i + 1) << ":" << std::endl;
std::cout << " unique_id: " << camera.uniqueId << std::endl;
}
return 0;
}
and here's my code for UVC control:
// clang++ -framework Foundation -framework IOKit uvc_test.cpp -o uvc_test
#include <iostream>
#include <CoreFoundation/CoreFoundation.h>
#include <IOKit/IOCFPlugIn.h>
#include <IOKit/IOKitLib.h>
#include <IOKit/IOMessage.h>
#include <IOKit/usb/IOUSBLib.h>
#include <IOKit/usb/USB.h>
CFStringRef CreateCFStringFromIORegistryKey(io_service_t ioService,
const char* key) {
CFStringRef keyString = CFStringCreateWithCString(kCFAllocatorDefault, key,
kCFStringEncodingUTF8);
if (!keyString)
return nullptr;
CFStringRef result = static_cast<CFStringRef>(
IORegistryEntryCreateCFProperty(ioService, keyString, kCFAllocatorDefault,
kIORegistryIterateRecursively));
CFRelease(keyString);
return result;
}
std::string GetStringFromIORegistry(io_service_t ioService, const char* key) {
CFStringRef cfString = CreateCFStringFromIORegistryKey(ioService, key);
if (!cfString)
return "";
char buffer[256];
Boolean success = CFStringGetCString(cfString, buffer, sizeof(buffer),
kCFStringEncodingUTF8);
CFRelease(cfString);
return success ? std::string(buffer) : std::string("");
}
uint32_t GetUInt32FromIORegistry(io_service_t ioService, const char* key) {
CFStringRef keyString = CFStringCreateWithCString(kCFAllocatorDefault, key,
kCFStringEncodingUTF8);
if (!keyString)
return 0;
CFNumberRef number = static_cast<CFNumberRef>(
IORegistryEntryCreateCFProperty(ioService, keyString, kCFAllocatorDefault,
kIORegistryIterateRecursively));
CFRelease(keyString);
if (!number)
return 0;
uint32_t value = 0;
CFNumberGetValue(number, kCFNumberSInt32Type, &value);
CFRelease(number);
return value;
}
int main() {
// Get matching dictionary for USB devices
CFMutableDictionaryRef matchingDict =
IOServiceMatching(kIOUSBDeviceClassName);
// Get iterator for matching services
io_iterator_t serviceIterator;
IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict,
&serviceIterator);
// Iterate through matching devices
io_service_t usbService;
while ((usbService = IOIteratorNext(serviceIterator))) {
uint32_t locationId = GetUInt32FromIORegistry(usbService, "locationID");
uint32_t vendorId = GetUInt32FromIORegistry(usbService, "idVendor");
uint32_t productId = GetUInt32FromIORegistry(usbService, "idProduct");
IOCFPlugInInterface** plugInInterface = nullptr;
IOUSBDeviceInterface** deviceInterface = nullptr;
SInt32 score;
// Get device plugin interface
IOCreatePlugInInterfaceForService(usbService, kIOUSBDeviceUserClientTypeID,
kIOCFPlugInInterfaceID, &plugInInterface,
&score);
// Get device interface
(*plugInInterface)
->QueryInterface(plugInInterface,
CFUUIDGetUUIDBytes(kIOUSBDeviceInterfaceID),
(LPVOID*)&deviceInterface);
(*plugInInterface)->Release(plugInInterface);
// Try to find UVC control interface using CreateInterfaceIterator
io_iterator_t interfaceIterator;
IOUSBFindInterfaceRequest interfaceRequest;
interfaceRequest.bInterfaceClass = kUSBVideoInterfaceClass; // 14
interfaceRequest.bInterfaceSubClass = kUSBVideoControlSubClass; // 1
interfaceRequest.bInterfaceProtocol = kIOUSBFindInterfaceDontCare;
interfaceRequest.bAlternateSetting = kIOUSBFindInterfaceDontCare;
(*deviceInterface)
->CreateInterfaceIterator(deviceInterface, &interfaceRequest,
&interfaceIterator);
(*deviceInterface)->Release(deviceInterface);
io_service_t usbInterface = IOIteratorNext(interfaceIterator);
IOObjectRelease(interfaceIterator);
if (usbInterface) {
std::cout << "Get UVC device with:" << std::endl;
std::cout << "locationId: " << std::hex << locationId << std::endl;
std::cout << "vendorId: " << std::hex << vendorId << std::endl;
std::cout << "productId: " << std::hex << productId << std::endl
<< std::endl;
IOObjectRelease(usbInterface);
}
IOObjectRelease(usbService);
}
IOObjectRelease(serviceIterator);
}
