Coded Multisource Media Format

Description

Coded Multisource Media Format (CMMF) is a media container and coding format introduced in 3GPP Release 19 as part of the ongoing evolution of 5G media streaming and immersive service enablers. It is specified in TS 26.512 (5G Media Streaming) and TS 26.804 (Study on Media Handling for Multisource Media). CMMF defines how media originating from multiple capture points — such as multiple cameras, microphones, or sensor arrays — is coded, packaged, and signalled so that a receiving client can reconstruct a coherent, synchronized presentation. This is essential for emerging services like free-viewpoint video, volumetric video, multi-camera live streaming, and immersive audio, where a single monolithic media stream is insufficient.

Architecturally, CMMF sits at the media format layer within the 5G Media Streaming (5GMS) framework. It builds on established 3GPP media delivery mechanisms such as DASH and CMAF, extending them with multisource-specific metadata. The format defines a structured way to describe the relationship between multiple media components: which sources belong to the same scene, their spatial and temporal alignment, and the coding dependencies between them. Each source may be encoded independently or jointly, and CMMF provides the signalling needed for a client to select, decode, and render the appropriate subset of sources based on the user's viewpoint or device capabilities.

A key aspect of CMMF is synchronization. Because multiple sources are captured and encoded separately, they must be aligned in both time and space. CMMF includes timing information, source geometry descriptors, and reference anchors that allow the client to align streams accurately. This is particularly important for free-viewpoint applications, where the user can switch between camera angles or interpolate between viewpoints; any misalignment would be perceptible as visual or audio artifacts. The format also supports partial delivery, allowing clients to request only the sources relevant to their current view, which reduces bandwidth consumption.

CMMF is designed to be codec-agnostic, meaning it can carry media encoded with different codecs (e.g., VVC, HEVC, AV1) and different media types (video, audio, metadata). This flexibility ensures that it can evolve alongside codec advancements without requiring a complete redesign. It also integrates with 3GPP's QoS and network slicing mechanisms, enabling operators to allocate appropriate resources for multisource sessions, which are typically more bandwidth-intensive than traditional single-source streaming.

In the broader 3GPP ecosystem, CMMF complements other Rel-19 media enablers such as immersive audio and extended reality (XR) enhancements. It provides the format-level foundation that application-layer protocols and delivery frameworks can rely on. By standardizing how multisource media is represented, CMMF promotes interoperability between content producers, service providers, and device manufacturers, reducing fragmentation in the emerging multisource media market.

Purpose & Motivation

CMMF was created to address the lack of a standardized format for representing media captured from multiple sources in 3GPP streaming services. Prior to Rel-19, 3GPP media formats primarily targeted single-source content, with limited support for multiview or multisource scenarios. As immersive services such as free-viewpoint video, volumetric video, and multi-camera live events gained traction, the need for a common format that could describe, synchronize, and deliver multiple media sources became clear. Without such a standard, each vendor or service provider would implement proprietary solutions, leading to interoperability issues and limiting market growth.

The format solves several technical problems. First, it provides a unified way to signal the relationships between sources, enabling clients to understand which streams belong together and how they should be combined. Second, it defines synchronization mechanisms that ensure temporal and spatial alignment across sources, which is critical for seamless user experiences. Third, it supports selective delivery, allowing clients to request only the sources they need, thereby optimizing bandwidth usage. Finally, it is designed to be extensible and codec-agnostic, ensuring longevity as media technologies evolve.

Historically, 3GPP has progressively enhanced its media capabilities, starting with basic streaming in earlier releases and moving toward immersive and interactive services in 5G. CMMF represents a significant step in that evolution, providing the format-level infrastructure needed for next-generation media experiences. It builds on lessons learned from DASH and CMAF, extending them to the multisource domain and aligning with broader industry efforts in immersive media standardization.