Stream Player Control-流播放器控件
Posted boonya
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原文地址： https://www.codeproject.com/articles/885869/stream-player-control在本文中，您将会找到一个流播放器控件的实现。
- Download WPF demo - 12.9 MB
- Download WinForms demo - 12.6 MB
- Download WPF source - 10.2 KB
- Download WinForms source - 11.7 KB
- Download FFmpeg Facade source - 17.8 KB
介绍
这篇文章是我前一篇文章的一个延续，它展示了一个网络摄像头控件的实现。 最近我创建了另一个控件，并希望与社区分享我的经验。 这是一个基于FFmpeg的流播放器控件，可以执行以下操作：
该控件没有额外的依赖和一个简约的界面。
必要条件
- 该控件的WinForms版本是使用.NET Framework 2.0实现的
- 该控件的WPF版本是使用.NET Framework 4 Client Profile实现的
背景
现在通过互联网流式传输音频，视频和数据是非常平常的事情。 但是，当我试图找到一个.NET控件来播放通过网络发送的视频流时，我几乎找不到任何东西。 这个项目试图填补这个空白。
实现细节
如果你对实现细节不感兴趣，那么你可以跳过这一节。
实施分为三层。
- 底层被实现为本地DLL模块，它将我们的调用转发给FFmpeg框架。
- 为了便于分发，原生DLL模块作为资源嵌入到控件的程序集中。 在运行时阶段，DLL模块将被提取到磁盘上的临时文件，并通过后期绑定技术使用。 一旦控制权被处置，临时文件将被删除。 换句话说，该控件是作为一个单独的文件分发的。 所有这些操作都是由中间层来实现的。
- 顶层实现控制类本身。
只有顶层应该被客户使用。
底层
底层使用facade 模式来为FFmpeg框架提供一个简化的接口。 门面由三个类组成：StreamPlayer类，它实现了流播放功能
/// <summary>
/// The StreamPlayer class implements a stream playback functionality.
/// </summary>
class StreamPlayer : private boost::noncopyable
public:
/// <summary>
/// Initializes a new instance of the StreamPlayer class.
/// </summary>
StreamPlayer();
/// <summary>
/// Initializes the player.
/// </summary>
/// <param name="playerParams">The StreamPlayerParams object that contains the information that is used to initialize the player.</param>
void Initialize(StreamPlayerParams playerParams);
/// <summary>
/// Asynchronously plays a stream.
/// </summary>
/// <param name="streamUrl">The url of a stream to play.</param>
void StartPlay(std::string const& streamUrl);
/// <summary>
/// Retrieves the current frame being displayed by the player.
/// </summary>
/// <param name="bmpPtr">Address of a pointer to a byte that will receive the DIB.</param>
void GetCurrentFrame(uint8_t **bmpPtr);
/// <summary>
/// Retrieves the unstretched frame size, in pixels.
/// </summary>
/// <param name="widthPtr">A pointer to an int that will receive the width.</param>
/// <param name="heightPtr">A pointer to an int that will receive the height.</param>
void GetFrameSize(uint32_t *widthPtr, uint32_t *heightPtr);
/// <summary>
/// Uninitializes the player.
/// </summary>
void Uninitialize();
;Stream类将视频流转换为一系列帧
/// <summary>
/// A Stream class converts a stream into series of frames.
/// </summary>
class Stream : private boost::noncopyable
public:
/// <summary>
/// Initializes a new instance of the Stream class.
/// </summary>
/// <param name="streamUrl">The url of a stream to decode.</param>
Stream(std::string const& streamUrl);
/// <summary>
/// Gets the next frame in the stream.
/// </summary>
/// <returns>The next frame in the stream.</returns>
std::unique_ptr<Frame> GetNextFrame();
/// <summary>
/// Gets an interframe delay, in milliseconds.
/// </summary>
int32_t InterframeDelayInMilliseconds() const;
/// <summary>
/// Releases all resources used by the stream.
/// </summary>
~Stream();
;Frame类，它是一组框架相关的工具。
/// <summary>
/// The Frame class implements a set of frame-related utilities.
/// </summary>
class Frame : private boost::noncopyable
public:
/// <summary>
/// Initializes a new instance of the Frame class.
/// </summary>
Frame(uint32_t width, uint32_t height, AVPicture &avPicture);
/// <summary>
/// Gets the width, in pixels, of the frame.
/// </summary>
uint32_t Width() const return width_;
/// <summary>
/// Gets the height, in pixels, of the frame.
/// </summary>
uint32_t Height() const return height_;
/// <summary>
/// Draws the frame.
/// </summary>
/// <param name="window">A container window that frame should be drawn on.</param>
void Draw(HWND window);
/// <summary>
/// Converts the frame to a bitmap.
/// </summary>
/// <param name="bmpPtr">Address of a pointer to a byte that will receive the DIB.</param>
void ToBmp(uint8_t **bmpPtr);
/// <summary>
/// Releases all resources used by the frame.
/// </summary>
~Frame();
;这些树类是FFmpeg Facade DLL模块的核心。
中间层
中间层由StreamPlayerProxy类实现，该类用作FFmpeg Facade DLL模块的代理。
首先，我们应该从资源中提取FFmpeg Facade DLL模块并将其保存到一个临时文件中。
_dllFile = Path.GetTempFileName();
using (FileStream stream = new FileStream(_dllFile, FileMode.Create, FileAccess.Write))
using (BinaryWriter writer = new BinaryWriter(stream))
writer.Write(Resources.StreamPlayer);
然后我们将DLL模块加载到调用进程的地址空间中。
_hDll = LoadLibrary(_dllFile);
if (_hDll == IntPtr.Zero)
throw new Win32Exception(Marshal.GetLastWin32Error());
并将DLL模块函数绑定到类实例方法。
private delegate Int32 StopDelegate();
private StopDelegate _stop;
// ...
IntPtr procPtr = GetProcAddress(_hDll, "Stop");
_stop =
(StopDelegate)Marshal.GetDelegateForFunctionPointer(procPtr,
typeof(StopDelegate));在处理控件时，我们卸载DLL模块并将其删除。
private void Dispose()
if (_hDll != IntPtr.Zero)
FreeLibrary(_hDll);
_hDll = IntPtr.Zero;
if (File.Exists(_dllFile))
File.Delete(_dllFile);
顶层
顶层由具有以下接口的StreamPlayerControl类实现。
/// <summary>
/// Asynchronously plays a stream.
/// </summary>
/// <param name="uri">The url of a stream to play.</param>
/// <exception cref="ArgumentException">An invalid string is passed as an argument.</exception>
/// <exception cref="Win32Exception">Failed to load the FFmpeg facade dll.</exception>
/// <exception cref="StreamPlayerException">Failed to play the stream.</exception>
public void StartPlay(Uri uri)
/// <summary>
/// Retrieves the image being played.
/// </summary>
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