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