Posted on 2007-04-29 13:21
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简介
这篇文章解释了如何将使用DirectShow的应用程序转向使用vista上的Digital Media API，即Media Foundation.
本文假设你已经非常熟悉DirectShow。并且本文并不讲述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 |