从Directshow转向 Media Foundation

 

对比Media Foundation 和DirectShow

         我们已经跨入了对高清数字媒体时代。未来的数字高清将无处不在。但是他非常需要健壮的保护，而这是当前的数字媒体平台所不具备的。Media Fundation就是为了这个而存在。
        让我们审视高清数字，这个平台需要很有弹性，便于从小故障下恢复。需要考虑大量的不同品质的video 和audio.Media Foundation就是为了这个而存在。比如，支持下一代的HD技术：
  1：DirectX 视频加速(DXVA) 2.0提供了比DXVA1.0更高效率的视频加速，更稳定，最新的视频解码能力，和扩展的硬件视频加速。在DXVA2.0下，windows可以直接处理某些高清内容，并容易错误恢复。
2：Color-space能得以保存在整个视频处理流程中，所以中途可以无转换损失，用户可以享受到高逼真的画质。这个也能减少CPU等消耗。
3：增强的视频渲染器（enchanced video render EVR)增强了视频处理和时钟等。

        让我们研究一下文件保护，在用户购买了一部电影之后，他可以把电影传到他的某个设备上（一些设备支持直接在播放的时候录制），这个过程中会有多种保护模式，购买后的使用保护，播放时防录制保护，复制保护，如果某一个保护没有正确完成，就会使整套保护没有了意义。所以这需要有一个无缝的平台去相互协作。Media Foundation就是为了这个而存在。
        最后，让我们来总览一下DirectShow. DirectShow的API对这些数字高清媒体的应用程序确实是非常通用的，万能的，但是，DirectShow作为一个10多年的老技术而言已经力不从心了。比如：
   1：流程是静态static的，所以实现动态的Graph和Major format change是非常困难的。
  2：DirectShow filter的线程模型是非常复杂的，要完全理解并永不出错是太困难了。
  3：DirectShow filter只能用于DirectShow。
  4：DirectShow不支持文件保护。
  作为DirectShow的接替者，Media Foundation出现了，他不会马上替代DirectShow,作为第一步，他将在vista上慢慢展露他的影响。
  但是目前为止，Media Foundation只能在媒体保护（Proteced media process)）方面大施手脚,还未向DirectShow进行足够的扩展和替代。


Appendix: Feature Comparisons

The following table compares the features of Media Foundation with those of DirectShow.

Feature group	Feature	Media Foundation	DirectShow
Basic functionality	Audio and video rendering	Yes	Yes
	Event notification	Yes	Yes
	Device enumeration	No	Yes
	Component enumeration	Yes	Yes
	Synchronization to reference clock	Yes	Yes
	Seeking	Yes	Yes
	Improved stress resilience	Yes	No
Content protection	Component validation	Yes	No
	Content protection policy negotiation	Yes	No
	Interoperability between content protection technologies	Yes	No
	Protection against kernel-mode and user-mode threats	Yes	No
	Component revocation and renewal	Yes	No
	Video output protection management	Yes	Yes
Media tasks	Audio capture	No	Yes
	Video capture	No	Yes
	Video editing	No	Yes
	DVD playback and navigation	No	Yes
	MPEG-2 support	No	Yes
	ASF support	No	Yes
	TV technologies	No	Yes
	Stream buffer engine	No	Yes
	Encoder API	No	Yes
Video renderer	Substream mixing using per-pixel or planar alpha blending	Yes	Yes
	Customizable video composition	No	Yes
	Support for custom presenters	Yes	Yes
	Windowless rendering	Yes	Yes
	Multimonitor support	Yes	Yes
	DXVA	Yes	Yes
	DirectDraw exclusive mode	Yes	Yes
	Backward compatibility with existing applications	Yes	Yes
	Accurate frame stepping	Yes	Yes
	Alpha blending of image data	Yes	Yes
	Glitch resilience	Yes	No
	Enhanced video fidelity	Yes	No
	Enhanced content protection robustness	Yes	No
	Standalone use	Yes	No
	Standalone mixing component	Yes	No
Transforms (MFT or DMO)	Synchronous data processing	Yes	Yes
	Simple programming model	Yes	Yes
	Standalone use	Yes	Yes
	Multiple inputs and multiple outputs	Yes	Yes
	Dynamic number of streams	Yes	No
	Access to sample-level metadata	Yes	No
	In-place processing	Yes	Yes
	Dynamic format changes	Yes	No
	Quality adjustment	Yes	No
	Rate change	Yes	No

The following table compares the features of Media Foundation with those of the Windows Media Format SDK.

Feature group	Feature	Media Foundation	Format SDK
ASF file features	Audio and video streams	Yes	Yes
	Image streams	No	Yes
	Arbitrary streams (text, file, Web, custom data)	No	Yes
	Script commands	No	Yes
	Data unit extensions	Yes	Yes
	SMPTE time code support	No	Yes
	Mutual exclusion	Yes	Yes
	Stream prioritization	Yes	Yes
	Bandwidth sharing	No	Yes
	Indexes	Yes	Yes
	Markers	Yes	Yes
	Multiple bit rate stream	Yes	Yes
	Multiple language support	Yes	Yes
Codec features	CBR encoding	Yes	Yes
	VBR encoding	Yes	Yes
	Two-pass encoding	Yes	Yes
	High-resolution audio support	Yes	Yes
	Low delay audio	Yes	Yes
	S/PDIF audio output	Yes	Yes
	Video image	Yes	Yes
	Device conformance template	Yes	Yes
	Video complexity settings	Yes	Yes
	Frame interpolation	Yes	Yes
	DirectX Video Acceleration	Yes	Yes
File writing	Video resizing	Yes	Yes
	Color space conversion	Yes	Yes
	Audio resampling	Yes	Yes
	ASF file sink	Yes	Yes
	Network sinks	No	Yes
	Push sinks	No	Yes
	Watermarking support	No	Yes
	Input formats, input settings, and data unit extensions	Yes	Yes
	WMA smart recompression	No	Yes
	Multichannel audio	Yes	Yes
File reading	User-allocated sample support	No	Yes
	Synchronous reading	No	Yes
	Output format enumeration	Yes	Yes
	Multichannel audio	Yes	Yes
	MP3 support	Yes	Yes
	Network sources	Yes	Yes
Metadata	ID3 support	No	Yes
	Custom metadata	Yes	Yes
Digital rights management	Live DRM	No	Yes
	DRM Individualization	Yes	Yes
	Back up and restore DRM licenses	Yes	Yes
	View DRM attributes in the Metadata Editor	Yes	Yes
	Output protection levels	Yes	Yes
	License revocation	Yes	Yes
	Windows Media DRM for Network Devices	Yes	Yes
	Secure Audio Path	No	Yes
	Playlist burning	Yes	Yes
	Third-party transcription support	Yes	No
	Local license issuance	Yes	No
	Enhanced Windows Media DRM renewability	Yes	No

本文来自  http://www.cnitblog.com/vcommon/archive/2007/04/29/26384.html