從Directshow轉向 Media Foundation

 

對比Media Foundation 和DirectShow

         我們已經跨入了對高清數字媒體時代。未來的數字高清將無處不在。但是他非常需要健壯的保護，而這是當前的數字媒體平臺所不具備的。Media Fundation就是爲了這個而存在。
        讓我們審視高清數字，這個平臺需要很有彈性，便於從小故障下恢復。需要考慮大量的不同品質的video 和audio.Media Foundation就是爲了這個而存在。比如，支持下一代的HD技術：
  1：DirectX 視頻加速(DXVA) 2.0提供了比DXVA1.0更高效率的視頻加速，更穩定，最新的視頻解碼能力，和擴展的硬件視頻加速。在DXVA2.0下，windows可以直接處理某些高清內容，並容易錯誤恢復。
2：Color-space能得以保存在整個視頻處理流程中，所以中途可以無轉換損失，用戶可以享受到高逼真的畫質。這個也能減少CPU等消耗。
3：增強的視頻渲染器（enchanced video render EVR)增強了視頻處理和時鐘等。

        讓我們研究一下文件保護，在用戶購買了一部電影之後，他可以把電影傳到他的某個設備上（一些設備支持直接在播放的時候錄製），這個過程中會有多種保護模式，購買後的使用保護，播放時防錄製保護，複製保護，如果某一個保護沒有正確完成，就會使整套保護沒有了意義。所以這需要有一個無縫的平臺去相互協作。Media Foundation就是爲了這個而存在。
        最後，讓我們來總覽一下DirectShow. DirectShow的API對這些數字高清媒體的應用程序確實是非常通用的，萬能的，但是，DirectShow作爲一個10多年的老技術而言已經力不從心了。比如：
   1：流程是靜態static的，所以實現動態的Graph和Major format change是非常困難的。
  2：DirectShow filter的線程模型是非常複雜的，要完全理解並永不出錯是太困難了。
  3：DirectShow filter只能用於DirectShow。
  4：DirectShow不支持文件保護。
  作爲DirectShow的接替者，Media Foundation出現了，他不會馬上替代DirectShow,作爲第一步，他將在vista上慢慢展露他的影響。
  但是目前爲止，Media Foundation只能在媒體保護（Proteced media process)）方面大施手腳,還未向DirectShow進行足夠的擴展和替代。


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

本文來自  http://www.cnitblog.com/vcommon/archive/2007/04/29/26384.html