Content for TS 26.346 Word version: 19.1.0
M Guidelines for audiovisual streaming using HLS over MBMS broadcasts
M.1 Introduction
M.2 Guidelines
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M Guidelines for audiovisual streaming using HLS over MBMS broadcasts |R16| p. 271
M.1 Introduction p. 271
In order to interoperate with MBMS, the HLS client should be MBMS-aware. This allows it to take best advantage of broadcast content and unicast content when and where broadcast is not available.
The HLS Master Playlist of an asset pertains equally to both the broadcast and independent unicast availability of a media asset. Generally only a small subset of HLS Media Playlists published in a Master Playlist will be available via an MBMS broadcast. This subset is typically chosen to satisfy the union of all supported UE media decoder compatibilities. A shared Master Playlist is required to support the unicast fallback described in this clause.
M.2 Guidelines p. 271
M.2.1 Providing unicast fallback for both HLS and DASH p. 271
M.2.1.1 Recommended client support for unicast fallback p. 271
An MBMS-aware client should provide support for unicast fallback, although a content provider is not required to offer one. A simultaneous unicast and broadcast delivery provides a fallback for broadcast delivery. Moreover a simultaneous broadcast, with unicast fallback, affords clients the ability to transition between broadcast and non-broadcast domains such as transitioning from a WiFi to cellular service during presentation.
M.2.1.2 Recommended unicast availability for HLS and HLS/DASH Hybrid Services p. 271
It is recommended that both an MBMS HLS and Hybrid HLS/DASH service include a mechanism for unicast fallback. In this context, both the HLS Master Playlist and the unified DASH MPD serve the dual purpose of describing streams available via the MBMS bearer service and those available, separately, via unicast.
M.2.1.3 Implied unicast stream availability p. 271
In clause 7.6.2.2, Redundant Unicast Resource Specific Metadata, an explicit mechanism for nominating unicast availability is detailed. An MBMS-aware client should assume that any media playlist not included in an instance of r12:broadcastAppService is available via unicast.
M.2.2 Media Playlist delivery p. 271
The HLS Media Playlist specifies available segments of a given stream. Media Playlists for live content are updated each time a new segment is generated. In order to control the order of delivery, the Media Playlist corresponding to the broadcasted HLS Renditions should be delivered within the same MBMS session as the media segments.
It is recommended to transmit the updated Media Playlist with a new Content-MD5 value in the FLUTE FDT, so that the UE can identify new versions of Media Playlists. It is also recommended to use Cache-control directives in the FDT (clause 7.2.10.5) for Media Playlists, to provide an expiration date with the Expires subelement, so that the UE won't keep in cache an old version.
Following requirements from clause 5.7, the MBMS delivers media segment(s) and Media Playlist in such a way that the last packet of the delivered object (that represents the Media Playlist specifying a media segment) is transmitted after the last packet of the delivered object (that represents the said media segment), as illustrated in Figure M.2.2-1.
Figure M.2.2-1: Transmission of the media playlist within the MBMS session
(⇒ copy of original 3GPP image)
(⇒ copy of original 3GPP image)
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