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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備列表。C++獲取視頻設備列表的方法有不少，但C#獲取視頻設備列表的方法網上提供的解決方案基本都是依賴第三方庫的，為了獲取視頻設備列表而引入一整個視頻庫實在是不太必要。經過思考，Windows的directshow和mediafudation都是基于com的，而且C#對com的支持是很好的，基于上述兩點我們完全可以在C#中直接調用com。

一、定義com接口

我們使用directshow獲取視頻設備列表，由于com的跨語言特性，完全可以直接在C#中調用，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、枚舉設備

與directshow流程一樣，調用com枚舉設備即可，本文只展示獲取設備名稱（FriendlyName），獲取其他屬性可以參照c++調用directshow的實現。

        /// <summary>
        /// 枚舉視頻設備
        /// </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;
//枚舉設備
foreach (var i in EnumDevices.Devices)
{
    //打印設備名稱
    Console.WriteLine(i);
}

效果：

在這里插入圖片描述

總結

以上就是今天要講的內容，本文介紹了C#直接調用com獲取視頻設備列表的方法，只要知道了com的一些基本原理以及c#和com的關系，很容易就能實現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，只是筆者使用的環境中只需要枚舉視頻設備列表，不需要其他功能，引入完整的directshow接口有點大材小用，所以還不如自己定義幾個必要的接口來的實在。

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

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