AVCaptureDevice的USB接口

Question

如果我有一个AVCaptureDevice，我如何获得相关的USB接口，以便我可以访问底层硬件通过IOKit？

我尝试通过vid & pid找到它，但是如果我插入两个具有相同vid，pid的设备，这是行不通的。下面是从AVCaptureDevice中提取vid和pid的代码：

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithDeviceType:AVMediaTypeVideo];
NSString *modelID = [device modelID];

NSRange vidRange = [modelID rangeOfString:@"VendorID_"];
int vid = [[modelID substringWithRange:NSMakeRange(vidRange.location + 9, 5)] intValue];

NSRange pidRange = [modelID rangeOfString:@"ProductID_"];
int vid = [[modelID substringWithRange:NSMakeRange(pidRange.location + 10, 5)] intValue];

然后我搜索一个匹配的IOService：

CFMutableDictionaryRef matchingDict = IOServiceMatching(kIOUSBDeviceClassName);
CFNumberRef numberRef;

numberRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &vid);
CFDictionarySetValue(matchingDict, CFSTR(kUSBVendorID), numberRef);
CFRelease(numberRef);

numberRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &pid);
CFDictionarySetValue(matchingDict, CFSTR(kUSBProductID), numberRef);
CFRelease(numberRef);

io_service_t camera = IOServiceGetMatchingService(kIOMasterPortDefault, matchingDict);

Answer 1

也许AVCaptureDevice modelID和uniqueID的结合可以帮助您找到匹配的IOService。这两个ID的格式看起来既没有文档，又依赖于传输和媒体类型，但是您应该能够找出一些东西。以下是基于两种设备的USB音频(因为我没有任何USB摄像头)的暂定映射：

modelID: USB Headphone Set:0C76:1607
uniqueID: AppleUSBAudioEngine:Unknown Manufacturer:USB Headphone Set:14200000:2,1,
    USB Headphone Set:

    Product ID: 0x1607
    Vendor ID:  0x0c76  (Solid State System Co., Ltd.)
Version:    1.00
Speed:  Up to 12 Mb/sec
    Location ID:    0x14200000 / 9
    Current Available (mA): 1000
    Current Required (mA):  100
    Extra Operating Current (mA):   0


uniqueID: AppleUSBAudioEngine:Burr-Brown from TI              :USB Audio CODEC :14200000:2,
modelID: USB Audio CODEC :08BB:2902
    USB Audio CODEC :

    Product ID: 0x2902
    Vendor ID:  0x08bb  (Texas Instruments Japan)
Version:    1.00
Speed:  Up to 12 Mb/sec
Manufacturer:   Burr-Brown from TI
    Location ID:    0x14200000 / 10
    Current Available (mA): 1000
    Current Required (mA):  100
    Extra Operating Current (mA):   0

(usb音频)格式类似于

modelID: name:vendorID:productID
uniqueID: AppleUSBAudioEngine:Manufacturer or Unknown Manufacturer:location ID:???

如果USB视频的uniqueID类似，那么productID、vendorID和locationID (其中的USB端口)的组合应该足以唯一地识别底层设备的硬件，尽管其方式脆弱且无文档。