A great network media device must have a short boot time and respond to the user’s actions. To ensure that network media devices meet the expectations of today’s users, we make the following performance recommendations.
Device Startup Performance
For all network media devices, the time between turning on the device and the point at which the user can interact with the device should be less than 60 seconds.
When the device is playing non-transcoded, unprotected audio content, the elapsed time from the device playback start until the first sound is heard should be no more than 1 second. Transcoded audio should take no more than 3 seconds.
Track-to-Track Audio Latency
When the device is playing non-transcoded, unprotected audio content, the elapsed time from the last sound on one track to the first sound on the next track must be no more than 1 second. When the device is playing transcoded, unprotected audio content, or protected content, the elapsed time from the last sound on one track to the first sound on the next track must be no more than 3 seconds.
A great network media device should support gapless playback. Gapless playback means that tracks are played with no noticeable break between the tracks, so that an album plays continuously even though the CD is divided into tracks. The latency should be indiscernible by the human ear. This feature is important for listening to classical music, progressive rock, and electronic music.
When the device is playing unprotected video content, the elapsed time from the device playback start until the first video is displayed should be no more than 3 seconds. When the device is playing protected video content, the elapsed time from the device playback start until the first video is displayed should be no more than 8 seconds.
Track-to-Track Video Latency
When the device is playing unprotected video content, the elapsed time from the last video on one track to the first video on the next track must be no more than 3 seconds. When the device is playing protected video content, the time elapsed from the last video on one track to the first video on the next track must be no more than 6 seconds.
Building a Great Digital Media Renderer
Windows 7 has embraced the DLNA 1.5 specification for devices. As shown in scenario 3 in Figure 1, Windows lets users browse content on servers and send the content to digital media renderers. The DLNA requirements for DMR devices ensure good interoperability between DMR devices and the rest of the DLNA environment. In addition to the requirements that DLNA specifies, Windows has some requirements and recommendations to help device partners create great DMR devices.
Codec and Digital Rights Management Support
DLNA clearly defines the minimal set of codecs that are required for interoperability. Unfortunately, users’ libraries often consist of many different codecs that the device might not support. To address the growing number of codecs, Windows 7 NSS transcodes source content to several different profiles for better interoperability. The DMR device should support Windows Media codecs and specify the correct resource (RES) element for a format and bit rate the device supports.
Support for Windows Media Codecs
Windows Media Format codecs are publically available and are an optional format in the DLNA specification.
Windows Media Audio Support
If a DMR supports audio, the DMR should support the following WMA profiles as specified in the DLNA 1.5 Media Formats specification (NETMEDIA-0024):
Windows Media Video Support
If a DMR supports video, the DMR should support the following WMV profiles, as specified in the DLNA 1.5 Media Formats specification (NETMEDIA-0023):
Windows Media Audio and Windows Media Video Certified Codecs
If WMA and WMV are implemented, a DMR must use WMA and WMV decoders that have passed the Microsoft integrated circuit (IC) test (NETMEDIA-0001).
Playing the Correct RES Element
The Windows 7 NSS transcodes source content into different RES elements. A DMR must choose a RES element that the DMR device can display (NETMEDIA-0025). The DMR device should select any RES element that can be rendered without requiring a transcode operation. If the device can play RES element #1, the device should prefer that element over a transcoded element.
Some devices choose MPEG over other formats they support. This can create a poor experience if the user must endure a transcode even though the device supports the source media natively.
Devices should not choose to play or evaluate support for the media based only on the first returned RES element, even though Windows could provide the media to the device in a supported codec.
With Windows 7 transcode support, the DMR device is not required to support as many decoders.
Digital Rights Management
Windows Media Digital Rights Management (DRM) has been part of the Windows ecosystem since before the beta release of Windows Media Player 7 in 2000. Windows users have millions of protected files that must play in this ecosystem. Therefore, we highly recommend that digital media renderers support Windows Media DRM-ND (NETMEDIA-0020).
Digital media renderer devices must meet two criteria:
DMR devices must not block during errors.
DMR devices must be ready to accept input.
The DMR might not be in the same room as the DMC. Therefore, when an error occurs, it is often the best user experience to move past the error and continue to play the next item. The Windows 7 logo requires that when a DMR receives an error, it must go into a STOPPED state and await instructions from the DMC. If the DMC provides another resource, then the DMR must suppress any error and begin playback of the next stream (NETMEDIA-0041).
When a DMR announces itself on the network, it must be able to display streams that are received from a DMC without any additional user input (NETMEDIA-0042). It is unacceptable for a device to announce itself as a DMR and then refuse to play back because the hardware is not set up to receive content. If the device has multiple modes and it can act as a DMR only in certain modes, then it must not broadcast itself as a DMR when in one of those competing modes.