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C#?使用com獲取Windows攝像頭列表_C#教程

作者：CodeOfCC ? 更新時(shí)間： 2022-09-30 編程語言

前言

想使用ffmpeg打開攝像頭，需要輸入攝像頭的名稱，而ffmpeg本身的枚舉攝像頭列表功能不是接口
，所以需要用其他方式獲取到設(shè)備列表。C++獲取視頻設(shè)備列表的方法有不少，但C#獲取視頻設(shè)備列表的方法網(wǎng)上提供的解決方案基本都是依賴第三方庫的，為了獲取視頻設(shè)備列表而引入一整個(gè)視頻庫實(shí)在是不太必要。經(jīng)過思考，Windows的directshow和mediafudation都是基于com的，而且C#對(duì)com的支持是很好的，基于上述兩點(diǎn)我們完全可以在C#中直接調(diào)用com。

一、定義com接口

我們使用directshow獲取視頻設(shè)備列表，由于com的跨語言特性，完全可以直接在C#中調(diào)用，而不用通過C++封裝一層dll給C#使用。我們首先定義需要的com對(duì)象接口。

static readonly Guid SystemDeviceEnum = new Guid(0x62BE5D10, 0x60EB, 0x11D0, 0xBD, 0x3B, 0x00, 0xA0, 0xC9, 0x11, 0xCE, 0x86);
static readonly Guid VideoInputDevice = new Guid(0x860BB310, 0x5D01, 0x11D0, 0xBD, 0x3B, 0x00, 0xA0, 0xC9, 0x11, 0xCE, 0x86);
[Flags]
enum CDef
{
    None = 0x0,
    ClassDefault = 0x1,
    BypassClassManager = 0x2,
    ClassLegacy = 0x4,
    MeritAboveDoNotUse = 0x8,
    DevmonCMGRDevice = 0x10,
    DevmonDMO = 0x20,
    DevmonPNPDevice = 0x40,
    DevmonFilter = 0x80,
    DevmonSelectiveMask = 0xF0
}
[ComImport]
[SuppressUnmanagedCodeSecurity]
[Guid("3127CA40-446E-11CE-8135-00AA004BB851")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IErrorLog
{
    [PreserveSig]
    int AddError([In][MarshalAs(UnmanagedType.LPWStr)] string pszPropName, [In] System.Runtime.InteropServices.ComTypes.EXCEPINFO pExcepInfo);
}
[ComImport]
[Localizable(false)]
[SuppressUnmanagedCodeSecurity]
[Guid("55272A00-42CB-11CE-8135-00AA004BB851")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IPropertyBag
{
    [PreserveSig]
    int Read([In][MarshalAs(UnmanagedType.LPWStr)] string pszPropName, [MarshalAs(UnmanagedType.Struct)] out object pVar, [In] IErrorLog pErrorLog);

    [PreserveSig]
    int Write([In][MarshalAs(UnmanagedType.LPWStr)] string pszPropName, [In][MarshalAs(UnmanagedType.Struct)] ref object pVar);
}

[ComImport]
[SuppressUnmanagedCodeSecurity]
[Guid("29840822-5B84-11D0-BD3B-00A0C911CE86")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface ICreateDevEnum
{
    [PreserveSig]
    int CreateClassEnumerator([In][MarshalAs(UnmanagedType.LPStruct)] Guid pType, out IEnumMoniker ppEnumMoniker, [In] CDef dwFlags);
}

二、枚舉設(shè)備

與directshow流程一樣，調(diào)用com枚舉設(shè)備即可，本文只展示獲取設(shè)備名稱（FriendlyName），獲取其他屬性可以參照c++調(diào)用directshow的實(shí)現(xiàn)。

        /// <summary>
        /// 枚舉視頻設(shè)備
        /// </summary>
        public static IEnumerable<string> Devices
        {
            get
            {
                IMoniker[] monikers = new IMoniker[5];
                var devEnum = Activator.CreateInstance(Type.GetTypeFromCLSID(SystemDeviceEnum)) as ICreateDevEnum;
                IEnumMoniker moniker;
                if (devEnum.CreateClassEnumerator(VideoInputDevice, out moniker, 0) == 0)
                {
                    while (true)
                    {
                        int r = moniker.Next(1, monikers, IntPtr.Zero);
                        if (r != 0 || monikers[0] == null)
                            break;
                        yield return GetName(monikers[0]);
                        foreach (var i in monikers)
                        {
                            if(i!=null)
                            Marshal.ReleaseComObject(i);
                        }                      
                    }
                    Marshal.ReleaseComObject(moniker);
                }
                Marshal.ReleaseComObject(devEnum);
            }
        }
        /// <summary>
        /// 獲取設(shè)備名稱
        /// </summary>
        /// <param name="moniker"></param>
        /// <returns></returns>
        static string GetName(IMoniker moniker)
        {
            IPropertyBag property;
            object value;
            object temp = null;
            try
            {
                Guid guid = typeof(IPropertyBag).GUID;
                moniker.BindToStorage(null, null, ref guid, out temp);
                property = temp as IPropertyBag;
                int hr = property.Read("FriendlyName", out value, null);
                Marshal.ThrowExceptionForHR(hr);
                return value as string;
            }
            catch (Exception)
            {
                return null;
            }
            finally
            {
                if (temp != null)
                {
                    Marshal.ReleaseComObject(temp);
                }
            }
        }

三、完整代碼

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;
using System.Security;
namespace AC
{
    public class EnumDevices
    {
        /// <summary>
        /// 枚舉視頻設(shè)備
        /// </summary>
        public static IEnumerable<string> Devices
        {
            get
            {
                IMoniker[] monikers = new IMoniker[5];
                var devEnum = Activator.CreateInstance(Type.GetTypeFromCLSID(SystemDeviceEnum)) as ICreateDevEnum;
                IEnumMoniker moniker;
                if (devEnum.CreateClassEnumerator(VideoInputDevice, out moniker, 0) == 0)
                {
                    while (true)
                    {
                        int hr = moniker.Next(1, monikers, IntPtr.Zero);
                        if (hr != 0 || monikers[0] == null)
                            break;
                        yield return GetName(monikers[0]);
                        foreach (var i in monikers)
                        {
                            if(i!=null)
                            Marshal.ReleaseComObject(i);
                        }                      
                    }
                    Marshal.ReleaseComObject(moniker);
                }
                Marshal.ReleaseComObject(devEnum);
            }
        }
        /// <summary>
        /// 獲取設(shè)備名稱
        /// </summary>
        /// <param name="moniker"></param>
        /// <returns></returns>
        static string GetName(IMoniker moniker)
        {
            IPropertyBag property;
            object value;
            object temp = null;
            try
            {
                Guid guid = typeof(IPropertyBag).GUID;
                moniker.BindToStorage(null, null, ref guid, out temp);
                property = temp as IPropertyBag;
                int hr = property.Read("FriendlyName", out value, null);
                Marshal.ThrowExceptionForHR(hr);
                return value as string;
            }
            catch (Exception)
            {
                return null;
            }
            finally
            {
                if (temp != null)
                {
                    Marshal.ReleaseComObject(temp);
                }
            }
        }
        static readonly Guid SystemDeviceEnum = new Guid(0x62BE5D10, 0x60EB, 0x11D0, 0xBD, 0x3B, 0x00, 0xA0, 0xC9, 0x11, 0xCE, 0x86);
        static readonly Guid VideoInputDevice = new Guid(0x860BB310, 0x5D01, 0x11D0, 0xBD, 0x3B, 0x00, 0xA0, 0xC9, 0x11, 0xCE, 0x86);
        [Flags]
        enum CDef
        {
            None = 0x0,
            ClassDefault = 0x1,
            BypassClassManager = 0x2,
            ClassLegacy = 0x4,
            MeritAboveDoNotUse = 0x8,
            DevmonCMGRDevice = 0x10,
            DevmonDMO = 0x20,
            DevmonPNPDevice = 0x40,
            DevmonFilter = 0x80,
            DevmonSelectiveMask = 0xF0
        }
        [ComImport]
        [SuppressUnmanagedCodeSecurity]
        [Guid("3127CA40-446E-11CE-8135-00AA004BB851")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        interface IErrorLog
        {
            [PreserveSig]
            int AddError([In][MarshalAs(UnmanagedType.LPWStr)] string pszPropName, [In] System.Runtime.InteropServices.ComTypes.EXCEPINFO pExcepInfo);
        }
        [ComImport]
        [Localizable(false)]
        [SuppressUnmanagedCodeSecurity]
        [Guid("55272A00-42CB-11CE-8135-00AA004BB851")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        interface IPropertyBag
        {
            [PreserveSig]
            int Read([In][MarshalAs(UnmanagedType.LPWStr)] string pszPropName, [MarshalAs(UnmanagedType.Struct)] out object pVar, [In] IErrorLog pErrorLog);

            [PreserveSig]
            int Write([In][MarshalAs(UnmanagedType.LPWStr)] string pszPropName, [In][MarshalAs(UnmanagedType.Struct)] ref object pVar);
        }

        [ComImport]
        [SuppressUnmanagedCodeSecurity]
        [Guid("29840822-5B84-11D0-BD3B-00A0C911CE86")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        interface ICreateDevEnum
        {
            [PreserveSig]
            int CreateClassEnumerator([In][MarshalAs(UnmanagedType.LPStruct)] Guid pType, out IEnumMoniker ppEnumMoniker, [In] CDef dwFlags);
        }      
    }
}

四、使用示例

.net 6.0代碼示例如下

// See https://aka.ms/new-console-template for more information
using AC;
//枚舉設(shè)備
foreach (var i in EnumDevices.Devices)
{
    //打印設(shè)備名稱
    Console.WriteLine(i);
}

效果：

在這里插入圖片描述

總結(jié)

以上就是今天要講的內(nèi)容，本文介紹了C#直接調(diào)用com獲取視頻設(shè)備列表的方法，只要知道了com的一些基本原理以及c#和com的關(guān)系，很容易就能實(shí)現(xiàn)c#直接使用directshow的功能，第三方的庫也是做了類似的工作，定義了完整的directshow的接口，只是筆者使用的環(huán)境中只需要枚舉視頻設(shè)備列表，不需要其他功能，引入完整的directshow接口有點(diǎn)大材小用，所以還不如自己定義幾個(gè)必要的接口來的實(shí)在。

原文鏈接：https://blog.csdn.net/u013113678/article/details/123771254

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