微软媒体基金会应用开发指南

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"Developing Microsoft Media Foundation Applications" 是一本详细阐述如何使用 Microsoft Media Foundation 技术来开发音视频处理应用程序的书籍。该书由 Anton Polinger 编写，并获得了微软公司的授权。 Microsoft Media Foundation 是微软提供的一项核心技术，主要用于处理多媒体内容，包括音频和视频的编码、解码、捕获、播放以及传输。这个框架是 Windows 操作系统的一部分，旨在取代早期的 DirectShow 和 Windows Media Format SDK，提供了更高效、更现代的多媒体编程接口。在本书中，读者将深入学习 Media Foundation 的核心概念和组件，如 Media Session（媒体会话）、Transforms（转换）、Sources（源）和 Sinks（接收器）。Media Session 是整个框架的中心，负责协调媒体数据的流经路径。Transforms 包括编码器和解码器，用于处理音频和视频数据。Sources 提供媒体数据，可以是本地文件、网络流或者硬件设备。而 Sinks 则是接收并处理这些数据的目标，例如将数据输出到显示器或文件。书中可能涵盖了以下关键知识点： 1. **Media Foundation API**：讲解 Media Foundation API 的基本结构和用法，包括创建和管理 Media Sessions，以及如何使用 IMFTransform 接口进行编码和解码操作。 2. **编码与解码**：详细介绍如何使用 Media Foundation 支持的各种编码器和解码器，如 H.264 视频编码和 AAC 音频编码。 3. **多媒体数据处理**：阐述如何处理音频和视频数据流，包括格式转换、时间线同步和帧率控制。 4. **硬件加速**：讨论如何利用 GPU 进行硬件加速，以提高视频处理性能。 5. **实时流媒体**：介绍如何通过 Media Foundation 实现直播和点播流媒体服务。 6. **媒体捕获与回放**：详细说明如何使用 Media Foundation API 来从摄像头、麦克风等硬件设备捕获媒体，以及如何实现播放功能。 7. **错误处理和调试**：提供关于如何正确处理错误和异常的指导，以及如何使用调试工具进行问题排查。 8. **跨平台兼容性**：讨论 Media Foundation 在不同版本的 Windows 操作系统上的兼容性和差异。 9. **最佳实践和案例研究**：通过实际项目案例，展示如何在实际开发中有效应用 Media Foundation 技术。 10. **扩展与自定义**：介绍如何开发自定义的 Media Foundation 组件，如自定义 Transforms 或 Sources，以满足特定需求。通过学习本书，开发者能够掌握 Microsoft Media Foundation 技术，从而能够构建高效、稳定的多媒体应用程序，适用于各种应用场景，如视频会议、在线教育、娱乐应用以及专业级的音视频处理工具。

xiv Introduction

Assumptions

Because MF uses COM extensively, this book expects that you have a basic understand-

ing of C++ and COM technologies. If you do not yet have the knowledge of the core

COM ideas and APIs, you might consider reading Essential COM by Don Box (Addison-

Wesley Professional, 1998), or Inside COM by Dale Rogerson (Microsoft Press, 1997).

Though you can gain access to the MF APIs through managed wrappers and by

importing various MF functions, this book contains examples only in C++. You can use

managed code to access these APIs and attempt to follow along with the examples, but

be aware that a layer of managed code will add an extra level of complexity to your ap-

plications and make it more difcult to apply the concepts being discussed.

Who Should Not Read This Book

Not every book is aimed at every possible audience. If you do not have basic COM and

C++ experience, or if you’re not aiming to gain a thorough grounding in developing

media-based applications, this book is not for you.

Organization of This Book

This book is divided into nine chapters, each of which focuses on a different concept or

idea within Media Foundation. Though you can read the chapters independently from

each other, they gradually increase in complexity and assume a basic knowledge of the

ideas previously discussed.

Chapter 1, “Core Media Foundation Concepts,” and Chapter 2, “TopoEdit,” provide

a brief introduction to media playback technologies and an overview of basic MF

concepts. These chapters do not contain any code and are intended as a starter for

developers unfamiliar with the basic concepts behind MF. Chapter 3, “Media Playback,”

and Chapter 4, “Transcoding,” provide a grounding in MF application development,

demonstrating and discussing a simple media player and a transcoding application.

Chapter 5, “Media Foundation Transforms,” Chapter 6, “Media Foundation Sources,” and

Chapter 7, “Media Foundation Sinks,” discuss and show the design of core Media Foun-

dation components used in media processing pipelines. And nally, Chapter 8, “Custom

Media Sessions,” and Chapter 9, “Advanced Media Foundation Topics,” describe more

advanced concepts behind the MF platform and applications.

xviii Introduction

// Since pInterfaceObj pointer is guaranteed to not be NULL at this point, we

// can use it safely. Store the result in the hr.

hr = pInterfaceObj->Bar();

}

while(false);

// note that we did not need to call IUnknown::AddRef() or IUnknown::Release()

// for the pInterfaceObj pointer. That is because those calls are made

// automatically by the CComPtr smart pointer wrapper. The CComPtr smart pointer

// wrapper calls AddRef() during assignment, and calls Release() in the

// destructor. As a result, smart pointers help us eliminate many of the common

// COM reference counting issues.

return hr;

}

The core idea demonstrated by this sample function concerns the do-while loop. No-

tice that the while condition is set to false. This ensures that the do-while loop executes

only once, because the sole purpose of the do-while construct here is to provide a way

to break out of the standard code path and interrupt the execution if an error occurs.

The preceding SampleFunction() contains two function calls, one of which initial-

izes the pInterfaceObj pointer, and another that uses the pInterfaceObj pointer to call a

method of that object. The idea here is that if the rst Foo() function fails, the second

function should not—and cannot—be called, because the pInterfaceObj will not be

initialized properly. To ensure that the pInterfaceObj->Bar() method is not called if the

Foo() function fails, the code uses two C++ macros: BREAK_ON_FAIL() and BREAK_

ON_NULL(). The code behind those macros is extremely simple and is shown in the

example as well.

As you can see, the BREAK_ON_FAIL() macro will cause the execution to break out

of the do-while loop if the HRESULT returned from Foo() indicates a failure. This ar-

rangement lets you bypass the pInterfaceObj->Bar() call, so you can avoid an access

violation in the example. The BREAK_ON_NULL() macro functions similarly, except that

it also assigns an error code to the hr variable, which is returned as the result of the

SampleFunction().

Note I chose not to use the goto statements that developers sometimes

choose to handle these sorts of error conditions, because goto calls in C++

confuse the compiler and break compiler optimization. The code will still work

as expected, but the compiler will fail to optimize the binary properly. In addi-

tion, in my opinion, goto statements are ugly and should be avoided.

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