Media Format and Transport Model

The DLNA media format model is intended to achieve a baseline for network interoperability . while encouraging continued innovation in media codec technology. Improvements in media codec technology result in better network bandwidth utilization and media quality for a given bit rate. DLNA requirements on media format support apply to media content that passes over the home network from a DMS or M-DMS device to a DMP or M-DMP device. The DLNA media format model defines a set of required media formats and a set of optional media formats for each of the three classes of media and for both device categories: image, audio, and video with audio (AV). Table 1 and Table 2 show the current set of required formats and optional formats as defined in . the DLNA guidelines. The network interoperability model for media formats is as follows:

All DMS, DMP, DMR, DMC, and DMPr devices, and their counterpart MHD devices, must support all formats designated in Table 1 and Table 2 as required for any of the media classes and device category they support. In the addition, all DMS/M-DMS and DMP/M-DMP/M-DMD devices may support any additional formats designated as optional for any of the media classes they support.
Any DMP, M-DMP, DMR, M-DMD and DMPr device must be able to receive content from any DMS or M-DMS device. A DMS or M-DMS device may stream content in its native format if the receiving device supports such native format. Otherwise, that DMS or M-DMS device should transcode the native format to one of the applicable required formats or to a format understood by the rendering device.

Table 1. DLNA Media formats for Home Devices
Media Formats	Required Formats Set	Optional Formats Set
Imaging	JPEG	GIF, TIFF, PNG
Audio	LPCM (2 channel)	MP3, WMA9, AC-3, AAC, ATRAC3plus
Video	MPEG2	MPEG1, MPEG4, WMV9

Table 2. DLNA Media formats for Mobile/Handheld Devices
Media Formats	Required Formats Set	Optional Formats Set
Imaging	JPEG	GIF, TIFF, PNG
Audio	MP3 and MPEG4 AAC LC	MPEG4 (HE AAC, AAC LTP, BSAC), AMR, ATRAC3plus, G.726, WMA, LPCM
Video	MPEG4 AVC (AAC LC Assoc Audio)	VC1, H.263, MPEG4 part 2, MPEG2, MPEG4 AVC (BSAC or other for Assoc. Audio)

LPCM represents a reasonable technical choice for a required audio format in HND devices, particularly in wired environments. Wireless networking is rapidly growing in importance for home networking and is expected to become an important means of distributing media in the home. For a wireless device, or a resource-constrained device such as a portable player with limited memory and power supply, compressed audio formats, such as MP3, AAC and WMA provide more efficient use of network bandwidth, battery power and storage. Therefore for the MHD device category, MPEG4 AAC LC and MP3 were selected as mandatory formats in audio media class and AAC LC with efficient AVC video for A/V media class. MPEG4 AVC is a new digital video codec standard noted for achieving very high data compression while maintaining good video quality at bit rates that are substantially lower (e.g., half or less) than what previous standards would need. Also, MPEG4 AVC may be applied to a very wide variety of applications.

Over time, new media formats may be added to the required or optional format sets. However, at all times, the required set shall only include formats that are open standards. The required and optional formats model brings the benefit of continued innovation in media codec technologies while assuring interoperability. Device manufacturers can differentiate their products by also including support for one or more of the optional media formats. This allows manufacturers to take advantage of better audio and video formats and, when possible, make more efficient use of available media storage and network bandwidth resources without sacrificing interoperability with devices that only implement the required format set.

The transfer scenarios that can be supported include:

A transfer from a DMS or M-DMS device to a DMP or M-DMP device, even if there is no actual immediate rendering of the media content: This may occur for an intelligent DMS device that distributes or replicates media content on the home network.
A transfer from a DMS device to another DMS device: Note that the intelligent DMS device would logically be acting as a DMP device in this scenario even if there is no immediate rendering of the media content. This may occur for an intelligent DMS device that aggregates, organizes, processes, and/or archives media content on the home network.

DLNA has defined the following three types of media transfer modes to deliver content from . a Content Source to a Content Receiver:

Streaming Transfer is used when either a content binary is being immediately rendered by DMP, M-DMP or DMR for a user and contains inherent timing that must be met or a content binary is being generated in real time at a fixed rate (such as a live broadcast stream), regardless of whether the item is being immediately rendered or stored for later use.
Interactive Transfer is used when content that does not contain internal timing information is being transferred for the purpose of immediate user interaction with the content. For example, sending images that are to be displayed immediately to a user.
Background Transfer is used for the case where the content binary is not being transferred for immediate rendering or where the user may be satisfied with a transfer executed at the lowest priority. It is typically reserved for the download or upload of content (by M-DMD or M-DMU) that is not being generated in real time by the Content Source.

Devices that source or render media content across the home network must support HTTP as the mandatory transport. Those devices may also support optional RTP.

Why DLNA?

Media Format and Transport Model