摘录----What Is MTP? (Sidebar)
What Is MTP? (Sidebar)
Posted: Sep. 6, 2004
Media Transfer Protocol (MTP) is a new protocol and accompanying set of drivers developed by Microsoft to connect portable devices to a Windows XP PC and synchronize digital media content between those devices and the PC. MTP is geared toward portable devices with hard drives; flash-based devices will continue to use Mass Storage Class (MSC), a broadly supported protocol whose drivers are already included with Windows XP, 2000, and Me. In general, users will have to buy new devices that support MTP, although some existing devices will be upgradeable.
Among the benefits of MTP are the following:
Driverless installation. Previously, manufacturers of hard-drive-based portable media players had to write their own drivers to run on top of the Windows Media Device Manager (WMDM) API. This could cause installation headaches and hardware conflicts, and sometimes required users to install and use custom software to transfer files. In contrast, all MTP-compatible devices use drivers that Microsoft is shipping with Windows Media Player 10, and users will be able to perform all transfer and synchronization functions from within the Player.
AutoSync. Previously, many portable devices forced users to take action, such as dragging and dropping files or opening a special software application, to transfer files from the PC. In contrast, all MTP-compatible devices will support a new feature called AutoSync, which lets users configure Windows Media Player 10 to automatically transfer all newly acquired or ripped content to a device whenever it's connected. AutoSync is customizable so that the Player will transfer only content that meets certain criteria (songs rated four stars or higher, for instance), a capability that becomes important as media libraries on a PC grow beyond the hard drive capacity of a particular device. (MSC-based devices will also support AutoSync when used with Windows Media Player 10.)
Understand device limitations. MTP allows the PC to recognize a device's limitations, such as capacity or lack of support for certain file types. As new content is added to the PC, the Player will automatically transcode it (change the file type or compression ratio) in the background if necessary so it will be ready for transfer the next time the user connects the device. Transcoding was previously a manual process and was particularly unwieldy for transferring content such as recorded TV programs, for which the transcode time exceeds the playback time.
Bidirectional file property synchronization. Today, changes made to file properties (such as a user rating) on a device cannot be propagated back to the PC when the device is reconnected. MTP-compatible devices won't have this limitation.
Device presence in Windows shell. All MTP-compatible devices will appear in the My Computer window for easy configuration (just as MSC-based devices appear as a separate drive today).
Support for Windows Media 10 digital rights management (DRM). MTP is necessary to support Microsoft's latest DRM scheme, which enables new scenarios such as transferring subscription-based content to portable devices. (MTP is used to synchronize licenses between the PC and devices, among other functions.)
Based on PTP
MTP is based on Microsoft's Picture Transfer Protocol (PTP), which was introduced with Windows XP to ease the transfer and discovery of images from digital cameras.
In theory, Microsoft could have based its new technology for portable players on MSC, which is more broadly supported. However, Microsoft chose to work with PTP because MSC cannot support certain features, such as the following:
Hot unplug, the ability to unplug a device in the middle of a transfer without losing all material that had previously been transferred
Keeping the device's user interface active while it is connected to the PC
Controlling device functions from Windows
The ability to transfer data over IP networks (a future scenario—the first set of MTP-compatible devices will connect only via USB 2.0).
In addition to MSC, MTP joins at least two other synchronization protocols used to transfer digital media to portable devices: iSync, used by Apple's iPod, and SyncML, a standard proposed by the Open Mobile Alliance for synchronizing data between a PC and portable devices, such as mobile phones or handheld computers. Microsoft has no plans to support these protocols in the Windows Media Player, meaning that users will still have to install and use separate software to transfer material to devices that use these protocols.
