The NSS in Windows 7 and Windows Vista® supports HTTP and Real-Time Streaming Protocol (RTSP)/RTP protocols for delivering content to devices. The NSS in Windows XP supports streaming only over HTTP.
The Windows 7 NSS uses the Media Delivery Engine to deliver transcoded media content—content that is converted from one format to another—to the requesting device.
When the Windows 7 NSS exposes a media file to a device, it provides multiple resource elements for the content. One resource element specifies a URL for the content in its original format. The subsequent resource elements each specify a URL for a transcoded version of the content. A device can choose a resource element for which it has a codec to play back, and the NSS automatically transcodes the original format to the requested format. Formats supported for transcode by the Windows 7 NSS are listed in Table 6.
As mentioned earlier, Windows Media Player supports transcoding most supported input media formats to the preceding destination formats. This support means that digital media devices that implement the DMP and DMR role are not required to support all codecs to deliver a great playback experience. For example, if a user has video files that are all XVID, the Windows 7 NSS exposes the native XVID file to DMPs and DMRs, and also exposes a transcoded WMV and MPEG2 stream. This means that, even though the DMP and DMR do not support XVID, they still can provide a great playback experience for the consumer by requesting the WMV or MPEG2 format, where Windows automatically transcodes the XVID content.
The Windows 7 NSS provides multiple transcoded streams that use different codecs, and transcoded resource elements at different resolutions and bit rates. This option lets devices choose the stream that best meets their characteristics and bandwidth limitations. An example of this is a portable network device such as a Wi-Fi–capable mobile phone.
In Windows 7, users choose DMR devices in the network from a list that is provided by Windows Media Player or Windows Explorer and send content from PCs to the DMRs for playback. A DMR is a DLNA-defined networked device role. The DMR is the device in the network that plays content. The DMR implements the following three UPnP services:
Connection manager service, which lists all the media formats that the DMR supports.
AV transport service, which provides basic playback functions such as play, stop, and seek.
Rendering control service, which provides basic output control functions such as volume and brightness.
Figures 9 through 12 show the Windows 7 Play Tofeature that is available on the shortcut menu in Windows Media Player and Windows Explorer when one or more media items are selected. Media items can be selected in the local library or in other libraries. The Play To featureis also available from the playlist area of Windows Media Player. All media items that are dropped into the playlist area are sent to the selected DMR for playback.
Figure 9. The Play To feature on the shortcut menu in Windows Media Player showing multiple DMR devices available on the network
Figure 10. The Play To feature from the playlist area in Windows Media Player
Figure 11. The Play To feature on the shortcut menu of a group of media items from Karen's shared media library in Windows Media Player showing multiple DMR devices available on the network
Figure 12: The Play To feature on the shortcut menu of a group of media items in Windows Explorer showing multiple DMR devices available on the network
Content that is sourced from a shared Windows 7 media library is delivered to a DMR in a format that the device can play because of a hardware-accelerated transcoding engine. The Windows 7 transcoding ability includes audio and video for many new formats.
Windows 7 PCs interact with the connection manager service, AV transport service, and rendering control service to provide an end-to-end experience for media enthusiasts. A user selects content in a media library, selects a target DMR, and then plays the content. Windows 7 also performs the DMR role.
Figure 13 shows how users can enable this functionality in Windows Media Player from the prominently displayed Share menu. After enabling Windows Media Player to receive media on your network, other Windows 7 PCs and media controllers can discover the DMR and send content to the Player.
Figure 13. Windows Media Player displaying media-sharing features that let it act as a media renderer to receive content from other Windows 7 PCs and devices
Figure 14 shows the protocol layers in a DMR device. DMR devices support Wi-Fi or Ethernet for connectivity. They implement TCP/IP, UDP/IP, and HTTP, and implement the UPnP MediaRenderer functionality that includes the three services discussed earlier (connection manager, AV transport, and rendering control). DMR devices implement HTTP and extensions to receive content from a DMS in the network, and some use RTP for transfer.