Network Working Group M. Zanaty Internet-Draft S. Nandakumar Intended status: Informational Cisco Expires: 13 July 2024 P. Thatcher Microsoft 10 January 2024 Low Overhead Media Container draft-mzanaty-moq-loc-02 Abstract This specification describes a media container format for encoded and encrypted audio and video media data to be used primarily for interactive Media over QUIC Transport (MOQT) [MoQTransport], with the goal of it being a low-overhead format. It also defines the MOQ Catalog format for publishers to announce their tracks and for subscribers to consume them. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 13 July 2024. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction 1.1. Requirements Notation and Conventions 2. Payload Format 2.1. MOQ Object Mapping 2.2. LOC Header Metadata 2.2.1. Common Header Data 2.2.2. Video Header Data 2.2.3. Audio Header Data 2.2.4. Header Data Registration 3. Catalog 3.1. Catalog Fields 3.1.1. Base Fields 3.1.2. Extension Fields 3.1.3. Track Quality Profile 3.1.4. Track Relations 3.2. Catalog Retrieval 3.3. Catalog Examples 3.3.1. Lip Sync Audio/Video Tracks with single quality 3.3.2. Simulcast video tracks - 3 qualities 4. Payload Encryption 5. Container Serialization 6. Security Considerations 7. IANA Considerations 8. Normative References Appendix A. Acknowledgements Authors' Addresses 1. Introduction This specification describes a low-overhead media container format for encoded and encrypted audio and video media data, as well as a MOQ Catalog format to describe such tracks. "Low-overhead" refers to minimal extra encapsulation as well as minimal application overhead when interfacing with WebCodecs [WebCodecs]. The container format description is specified for all audio and video codecs defined in the WebCodecs Codec Registry [WEBCODECS-CODEC-REGISTRY]. The audio and video payload bitstream is identical to the "internal data" inside an EncodedAudioChunk and EncodedVideoChunk, respectively, specified in the registry. In addition to the media payloads, critical metadata is also specified for audio and video payloads. (Note: Align with MOQT terminology of either "metadata" or "header".) A primary motivation is to align with media formats used in WebCodecs to minimize extra encapsulation and application overhead when interfacing with WebCodecs. Other container formats like CMAF or RTP would require more extensive application overhead in format conversions, as well as larger encapsultion overhead which may burden some use cases like low bitrate audio scenarios. This specification can also be used by applications outside the context of WebCodecs or a web browser. While the media payloads are defined by referring to the "internal data" of an EncodedAudioChunk or EncodedVideoChunk in the WebCodecs Codec Registry, this "internal data" is the elementary bitstream format of codecs without any encapsulation. Referring to the WebCodecs Codec Registry avoids duplicating it in an identical IANA registry. * Section 2 defines the core media payload formats. * Section 2.2 defines the metadata associated with audio and video payloads. * Section 3 describes the MoQ Catalog format including examples. 1.1. Requirements Notation and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD","SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Payload Format The WebCodecs Codec Registry defines the contents of an EncodedAudioChunk and EncodedVideoChunk for the audio and video codec formats in the registry. The "internal data" in these chunks is used directly in this specification as the "LOC Payload" bitstream. This "internal data" is the elementary bitstream format of each codec without any encapsulation. For video formats with multiple bitstream formats in the WebCodecs Registry, such as H.264/AVC or H.265/HEVC, the LOC Payload uses the "canonical" format ("avcc" or "hevc", not "annexB") with the following additions: * Parameter sets are sent in the bitstream before key frames. * 4 byte lengths are sent before each NAL Unit. * No start codes or emulation prevention are used in the bitstream. * No additional codec configuration information ("extradata") is needed. 2.1. MOQ Object Mapping An application object when transported as a [MoQTransport] object is composed of a MOQ Object Header and its Payload. Media objects encoded using the container format defined in this specification populate the MOQ Object Payload with a LOC Header and LOC Payload as shown below. The LOC Payload is the "internal data" of an EncodedAudioChunk or EncodedVideoChunk. +--------------+----------+-----------+ | MOQ Object | LOC | LOC | | Header | Header | Payload | +--------------+----------------------+ <----------------------> MOQ Object Payload MOQ Object with LOC Container 2.2. LOC Header Metadata The LOC Header carries metadata for the corresponding LOC Payload. This metadata provides necessary information for intermediaries such as media switches to perform their media switching decisions when the payload is inaccessible due to encryption. Section Section 2.2.4 provides a framework for registering new LOC Header fields that aren't defined by this specification. 2.2.1. Common Header Data The following metadata MUST be captured for each media frame. Sequence Number: Identifies a sequentially increasing variable length integer that is incremented per encoded media frame. This may be replaced with the Object Sequence from the MOQ Object Header in cases where a MOQ Object is exactly one frame. Capture Timestamp in Microseconds: Captures the wall-clock time of the encoded media frame in a 64-bit unsigned integer. 2.2.2. Video Header Data Flags for frames which are independent, discardable, or base layer sync points, as well as temporal and spatial layer identification. [Framemarking] . 2.2.3. Audio Header Data Audio Level: Captures the magnitude of the audio level of the corresponding audio frame encoded in 7 bits as defined in section 3 of [RFC6464]. 2.2.4. Header Data Registration This section details the procedures to register header data fields that might be useful for a particular class of media applications. Registering a given metadata field requires the following attributes to be specified. Shortname: Short name for the metadata. (Not sent on the wire.) Description: Detailed description for the metadata. (Not sent on the wire.) ID: Identifier assigned by the registry. (varint) Length: Length of metadata value in bytes. (varint) Value: Value of metadata. (length bytes) Registration of type "Specification Required" is followed for registering new metadata in the LOC Header. 3. Catalog A Catalog is a MOQT Object that provides information about tracks from a given publisher. Catalog is used by subscribers for consuming tracks and for publishers to advertise the tracks. The content of "Catalog" is opaque to the Relays and may be end to end encrypted. Catalog provides the details of tracks such as Track IDs and corresponding media configuration details (audio/video codec detail, gamestate encoding details, for example) 3.1. Catalog Fields At the minumum catalog MUST provide enough information about MOQ Tracks, such as its full name, information about media for the track and mode of usage of the underlying QUIC transport. Following subsections identify the mandatory Section 3.1.1 fields and optional Section 3.1.2 fields that describe a given publisher's track in the catalog. The applications is free to add further fields to the catalog that is deemed necessary than the ones defined in this specification and they don't need to be standardized. TODO: Describe mechanics for preventing field name conflicts for future extensions and for application specific extensions. 3.1.1. Base Fields This section identifies the mandatory fields needs to be defined per track listed in the catalog. * Track Namespace: See section 2.3 of [MoQTransport] * Track Name: See section 2.3 of [MoQTransport] * Track Quality Profile: See Section 3.1.3 * Relation: See Section 3.1.4 Table 1 provides an overview of all base fields defined by this document. +=================+=======+===================+===========+ | Name | Label | Media Type | JSON Type | +=================+=======+===================+===========+ | Track Namespace | ns | AV | String | +-----------------+-------+-------------------+-----------+ | Track Name | tn | AV | String | +-----------------+-------+-------------------+-----------+ | QualityProfile | qp | See Section 3.1.3 | | +-----------------+-------+-------------------+-----------+ Table 1 3.1.2. Extension Fields Following optional extension fields may be supported by the application. * Temporal ID: Identifies the temporal layer/sub-layer encoded, starting with 0 for the base layer, and increasing with higher temporal fidelity. * Spatial ID: Identifies the spatial and quality layer encoded, starting with 0 for the base layer, and increasing with higher fidelity. * Depend: Identifies track dependencies for a given track. * Relation: See Section 3.1.4. Table 2 provides label and type identification for the extension fields +=============+===================+============+===========+ | Name | Label | Media Type | JSON Type | +=============+===================+============+===========+ | Temporal ID | tid | V | String | +-------------+-------------------+------------+-----------+ | Spatial ID | lid | V | String | +-------------+-------------------+------------+-----------+ | Depend | dep | V | Array | +-------------+-------------------+------------+-----------+ | Relation | See Section 3.1.4 | | | +-------------+-------------------+------------+-----------+ Table 2 3.1.3. Track Quality Profile Each track has an associated quality profile that describes the media objects for that track. Following properties identify a track's quality profile. * Codec: Codec information as defined by the codec registrations listed in [WEBCODECS-CODEC-REGISTRY]. * Framerate: As defined in section 7.8 of [WEBCODECS-CODEC-REGISTRY]. * Bitrate: As defined in section 7.7 and 7.8 of [WEBCODECS-CODEC-REGISTRY]. * SampleRate: As defined in section 7.7 of [WEBCODECS-CODEC-REGISTRY]. * Width,Height: As defined in section 7.8 of [WEBCODECS-CODEC-REGISTRY]. * ChanelCount: As defined in section 7.7 of [WEBCODECS-CODEC-REGISTRY]. * DisplayWidth, DisplayHeight: As defined in section 7.7 of [WEBCODECS-CODEC-REGISTRY]. Table 3 provides an overview of all QualityProfile fields defined by this document with their respective labels, applicable media types and data types. +===============+=======+============+===========+ | Name | Label | Media Type | JSON Type | +===============+=======+============+===========+ | Codec | cs | AV | String | +---------------+-------+------------+-----------+ | Framerate | fr | V | Number | +---------------+-------+------------+-----------+ | Bitrate | br | AV | Number | +---------------+-------+------------+-----------+ | Width | wd | V | Number | +---------------+-------+------------+-----------+ | Height | ht | V | Number | +---------------+-------+------------+-----------+ | SampleRate | sr | A | Number | +---------------+-------+------------+-----------+ | ChanelCount | cc | A | Number | +---------------+-------+------------+-----------+ | DisplayWidth | dw | V | Number | +---------------+-------+------------+-----------+ | DisplayHeight | dh | V | Number | +---------------+-------+------------+-----------+ Table 3 3.1.4. Track Relations Tracks can express dependency on other tracks via relations property. Following relation types are defined in this document. * time-aligned: Indicates set of tracks that share the same time offset when producing the media as well as considered as having same time offset when consuming the media. Typical example would be simulcasting a camera capture across multiple encoding qualities. * lip-sync: Indicates a synchronized playout of the media from the tracks identified. Example audio and video media synced for playout in a conference setting. * layered: Indicates tracks are dependent via layered encoding and applies to video tracks. Each track that is part of the layered relation set MUST include depend field listing the dependencies. Table 4 lists relation fields defined by this document with their respective labels, applicable media types and data types. +==============+=======+============+===========+ | Name | Label | Media Type | JSON Type | +==============+=======+============+===========+ | lip-sync | ls | AV | Array | +--------------+-------+------------+-----------+ | layered | ly | V | Number | +--------------+-------+------------+-----------+ | time-aligned | ta | AV | Number | +--------------+-------+------------+-----------+ Table 4 3.2. Catalog Retrieval On a successful connection setup, subscribers proceed by retrieving the catalog (if not already retrieved), subscribing to the tracks of their interest and consuming the data published as detailed below. Catalogs are identified as a special track, with its Track Name as "catalog". Catalog objects are retrieved by subscribing to its Full Track Name over its own MoQ control channel (Bidirectional QUIC Stream). I A successful subscription will lead to one or more catalog objects being published and implies authorization for subscribing to the tracks in the catalog. Unsuccessful subscriptions MUST result in closure of the MOQT session, followed by reporting the error obtained to the application. Catalog Objects obtained MUST parse successfully, otherwise MUST be treated as error, thus resulting the closure of the WebTransport session. 3.3. Catalog Examples The following section provides JSON examples of the catalog. 3.3.1. Lip Sync Audio/Video Tracks with single quality This example shows catalog for the media sender, Alice, capable of sending audio and video tracks and share lip-sync relation. { "ls": ["audio", "video"], [ { "ns": "conference.example.com/conference123/alice", "n": "video", "qp": "cs=av01.0.08M.10.0.110.09,wd=1920,ht=1080,fr=30" }, { "ns": "conference.example.com/conference123/alice", "n": "audio", "qp": "cs=opus,sr=48000,cc=2" } ], } 3.3.2. Simulcast video tracks - 3 qualities This example shows catalog for the media sender, Alice, capable of sending 3 video tracks for high definition, low definition and medium definition qualities in time-aligned relation. { "ta": ["hd", "sd", "md"], [ { "ns": "conference.example.com/conference123/alice", "n": "hd", "qp": "cs=av01,wd=1920,ht=1080,fr=30" }, { "ns": "conference.example.com/conference123/alice", "n": "md", "qp": "cs=av01,wd=720,ht=640,fr=30" }, { "ns": "conference.example.com/conference123/alice", "n": "sd", "qp": "cs=av01,wd=192,ht=144,fr=30" } ], } 4. Payload Encryption When end to end encryption is supported, the encoded payload is encrypted with keys from symmetric keying mechanisms, such a MLS, and the payload itself is protected using SFrame or other schemes similar schemes. TODO: Future revisions shall expand on the details on setting up such a scheme. 5. Container Serialization The wire encoding of the payload conforming to this specification is a set of length delimited values as shown below. The Bytes is obtained as output of AEAD operation for encrypting the Payload with the header data as additional data input. +--------+------------+-------+------------+ | Payload | Bytes | Payload | Bytes | | Len | (0) | Len (1) | (1) | ... +--------+------------+-------+------------+ 6. Security Considerations TODO 7. IANA Considerations A new IANA registry for LOC Header Metadata is defined and populated with the information in section Section 2.2.4. Specification required for new metadata registration. 8. Normative References [MoQTransport] Curley, L., Pugin, K., Nandakumar, S., and V. Vasiliev, "Media over QUIC Transport", Work in Progress, Internet- Draft, draft-ietf-moq-transport-01, 23 October 2023, . [Framemarking] Zanaty, M., Berger, E., and S. Nandakumar, "Video Frame Marking RTP Header Extension", Work in Progress, Internet- Draft, draft-ietf-avtext-framemarking-15, 26 July 2023, . [WebCodecs] "WebCodecs", July 2023, . [WEBCODECS-CODEC-REGISTRY] "WebCodecs Codec Registry", July 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6464] Lennox, J., Ed., Ivov, E., and E. Marocco, "A Real-time Transport Protocol (RTP) Header Extension for Client-to- Mixer Audio Level Indication", RFC 6464, DOI 10.17487/RFC6464, December 2011, . Appendix A. Acknowledgements Thanks to Cullen Jennings for suggestions and review. Authors' Addresses Mo Zanaty Cisco Email: mzanaty@cisco.com Suhas Nandakumar Cisco Email: snandaku@cisco.com Peter Thatcher Microsoft Email: pthatcher@microsoft.com