RFC-7845OggEncapsulationfortheOpusAudioCodec(Opus)资源-CSDN文库

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Internet Engineering Task Force (IETF) T. Terriberry

Request for Comments: 7845 Mozilla Corporation

Updates: 5334 R. Lee

Category: Standards Track Voicetronix

ISSN: 2070-1721 R. Giles

Mozilla Corporation

April 2016

Ogg Encapsulation for the Opus Audio Codec

Abstract

This document defines the Ogg encapsulation for the Opus interactive

speech and audio codec. This allows data encoded in the Opus format

to be stored in an Ogg logical bitstream.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force

(IETF). It represents the consensus of the IETF community. It has

received public review and has been approved for publication by the

Internet Engineering Steering Group (IESG). Further information on

Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,

and how to provide feedback on it may be obtained at

http://www.rfc-editor.org/info/rfc7845.

This document is subject to BCP 78 and the IETF Trust’s Legal

Provisions Relating to IETF Documents

(http://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 Simplified BSD License text as described in Section 4.e of

the Trust Legal Provisions and are provided without warranty as

described in the Simplified BSD License.

Terriberry, et al. Standards Track [Page 1]

RFC 7845 Ogg Opus April 2016

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3

3. Packet Organization . . . . . . . . . . . . . . . . . . . . . 4

4. Granule Position . . . . . . . . . . . . . . . . . . . . . . 6

4.1. Repairing Gaps in Real-Time Streams . . . . . . . . . . . 7

4.2. Pre-skip . . . . . . . . . . . . . . . . . . . . . . . . 9

4.3. PCM Sample Position . . . . . . . . . . . . . . . . . . . 9

4.4. End Trimming . . . . . . . . . . . . . . . . . . . . . . 10

4.5. Restrictions on the Initial Granule Position . . . . . . 10

4.6. Seeking and Pre-roll . . . . . . . . . . . . . . . . . . 11

5. Header Packets . . . . . . . . . . . . . . . . . . . . . . . 12

5.1. Identification Header . . . . . . . . . . . . . . . . . . 12

5.1.1. Channel Mapping . . . . . . . . . . . . . . . . . . . 16

5.2. Comment Header . . . . . . . . . . . . . . . . . . . . . 22

5.2.1. Tag Definitions . . . . . . . . . . . . . . . . . . . 25

6. Packet Size Limits . . . . . . . . . . . . . . . . . . . . . 26

7. Encoder Guidelines . . . . . . . . . . . . . . . . . . . . . 27

7.1. LPC Extrapolation . . . . . . . . . . . . . . . . . . . . 28

7.2. Continuous Chaining . . . . . . . . . . . . . . . . . . . 28

8. Security Considerations . . . . . . . . . . . . . . . . . . . 29

9. Content Type . . . . . . . . . . . . . . . . . . . . . . . . 30

10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31

11. References . . . . . . . . . . . . . . . . . . . . . . . . . 32

11.1. Normative References . . . . . . . . . . . . . . . . . . 32

11.2. Informative References . . . . . . . . . . . . . . . . . 33

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34

Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 35

1. Introduction

The IETF Opus codec is a low-latency audio codec optimized for both

voice and general-purpose audio. See [RFC6716] for technical

details. This document defines the encapsulation of Opus in a

continuous, logical Ogg bitstream [RFC3533]. Ogg encapsulation

provides Opus with a long-term storage format supporting all of the

essential features, including metadata, fast and accurate seeking,

corruption detection, recapture after errors, low overhead, and the

ability to multiplex Opus with other codecs (including video) with

minimal buffering. It also provides a live streamable format capable

of delivery over a reliable stream-oriented transport, without

requiring all the data (or even the total length of the data)

up-front, in a form that is identical to the on-disk storage format.

Ogg bitstreams are made up of a series of "pages", each of which

contains data from one or more "packets". Pages are the fundamental

unit of multiplexing in an Ogg stream. Each page is associated with

Terriberry, et al. Standards Track [Page 2]

RFC 7845 Ogg Opus April 2016

3. Packet Organization

An Ogg Opus stream is organized as follows (see Figure 1 for an

example).

Page 0 Pages 1 ... n Pages (n+1) ...

+------------+ +---+ +---+ ... +---+ +-----------+ +---------+ +--

| | | | | | | | | | | | |

|+----------+| |+-----------------+| |+-------------------+ +-----

|||ID Header|| || Comment Header || ||Audio Data Packet 1| | ...

|+----------+| |+-----------------+| |+-------------------+ +-----

| | | | | | | | | | | | |

+------------+ +---+ +---+ ... +---+ +-----------+ +---------+ +--

^ ^ ^

| | |

| | Mandatory Page Break

| |

| ID header is contained on a single page

’Beginning Of Stream’

Figure 1: Example Packet Organization for a Logical Ogg Opus Stream

There are two mandatory header packets. The first packet in the

logical Ogg bitstream MUST contain the identification (ID) header,

which uniquely identifies a stream as Opus audio. The format of this

header is defined in Section 5.1. It is placed alone (without any

other packet data) on the first page of the logical Ogg bitstream and

completes on that page. This page has its ’beginning of stream’ flag

set.

The second packet in the logical Ogg bitstream MUST contain the

comment header, which contains user-supplied metadata. The format of

this header is defined in Section 5.2. It MAY span multiple pages,

beginning on the second page of the logical stream. However many

pages it spans, the comment header packet MUST finish the page on

which it completes.

All subsequent pages are audio data pages, and the Ogg packets they

contain are audio data packets. Each audio data packet contains one

Opus packet for each of N different streams, where N is typically one

for mono or stereo, but MAY be greater than one for multichannel

audio. The value N is specified in the ID header (see

Section 5.1.1), and is fixed over the entire length of the logical

Ogg bitstream.

Terriberry, et al. Standards Track [Page 4]

RFC 7845 Ogg Opus April 2016

The first (N - 1) Opus packets, if any, are packed one after another

into the Ogg packet, using the self-delimiting framing from

Appendix B of [RFC6716]. The remaining Opus packet is packed at the

end of the Ogg packet using the regular, undelimited framing from

Section 3 of [RFC6716]. All of the Opus packets in a single Ogg

packet MUST be constrained to have the same duration. An

implementation of this specification SHOULD treat any Opus packet

whose duration is different from that of the first Opus packet in an

Ogg packet as if it were a malformed Opus packet with an invalid

Table Of Contents (TOC) sequence.

The TOC sequence at the beginning of each Opus packet indicates the

coding mode, audio bandwidth, channel count, duration (frame size),

and number of frames per packet, as described in Section 3.1

of [RFC6716]. The coding mode is one of SILK, Hybrid, or Constrained

Energy Lapped Transform (CELT). The combination of coding mode,

audio bandwidth, and frame size is referred to as the configuration

of an Opus packet.

Packets are placed into Ogg pages in order until the end of stream.

Audio data packets might span page boundaries. The first audio data

page could have the ’continued packet’ flag set (indicating the first

audio data packet is continued from a previous page) if, for example,

it was a live stream joined mid-broadcast, with the headers pasted on

the front. If a page has the ’continued packet’ flag set and one of

the following conditions is also true:

o the previous page with packet data does not end in a continued

packet (does not end with a lacing value of 255) OR

o the page sequence numbers are not consecutive,

then a demuxer MUST NOT attempt to decode the data for the first

packet on the page unless the demuxer has some special knowledge that

would allow it to interpret this data despite the missing pieces. An

implementation MUST treat a zero-octet audio data packet as if it

were a malformed Opus packet as described in Section 3.4

of [RFC6716].

A logical stream ends with a page with the ’end of stream’ flag set,

but implementations need to be prepared to deal with truncated

streams that do not have a page marked ’end of stream’. There is no

reason for the final packet on the last page to be a continued

packet, i.e., for the final lacing value to be 255. However,

demuxers might encounter such streams, possibly as the result of a

transfer that did not complete or of corruption. If a packet

Terriberry, et al. Standards Track [Page 5]

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