This specification defines a Media Source Extensions™ [MEDIA-SOURCE] byte stream format specification based on MPEG audio streams.

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1. Introduction

This specification defines segment formats for implementations that choose to support MPEG audio streams specified in ISO/IEC 11172-3:1993, ISO/IEC 13818-3:1998, and ISO/IEC 14496-3:2009.

It defines the MIME-types used to signal codecs, and provides the necessary format specific definitions for initialization segments, media segments, and random access points required by the byte stream formats section of the Media Source Extensions spec. It also defines extra behaviors and state that only apply to this byte stream format.

2. MIME-types

This section specifies the MIME-types that may be passed to isTypeSupported() or addSourceBuffer() for byte streams that conform to this specification.

The "codecs" MIME-type parameter MUST NOT be used with these MIME-types.

3. MPEG Audio Frames

The format of an MPEG Audio Frame depends on the MIME-type used.

4. Metadata Frames

Since ID3v1, ID3v2 metadata frames, and Icecast headers are common in existing MPEG audio streams, implementations SHOULD gracefully handle such frames. Zero or more of these metadata frames are allowed to occur before, after, or between MPEG Audio Frames. Minimal implementations MUST accept, consume, and ignore these frames. More advanced implementations MAY choose to expose the metadata information via an inband TextTrack or some other mechanism.

4.1 Icecast headers

There is no normative spec for Icecast/SHOUTcast headers, just examples. For the purpose of this specification, an Icecast header is defined as beginning with the 4 character sequence "ICY "(U+0049 I, U+0043 C, U+0059 Y, U+0020 SPACE) and ending with a pair of carriage-return line-feed sequences (U+000D CARRIAGE RETURN, U+000A LINE FEED, U+000D CARRIAGE RETURN, U+000A LINE FEED).


Icecast headers are allowed in the byte streams because some Icecast and SHOUTcast servers return a status line that looks like "ICY OK 200" instead of a standard HTTP status line. User-agent network stacks typically interpret this as an HTTP 0.9 response and include the header in the response body. Allowing these headers to appear provides a simple way to interoperate with these servers.

5. Segment Definitions

The MPEG audio byte stream is a combination of one or more MPEG Audio Frames and zero or more Metadata Frames.

6. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, MUST NOT, and SHOULD are to be interpreted as described in [RFC2119].

A. References

A.1 Normative references

Matthew Wolenetz; Jerry Smith; Mark Watson; Aaron Colwell; Adrian Bateman. W3C. Media Source Extensions. 5 July 2016. W3C Candidate Recommendation. URL: https://www.w3.org/TR/media-source/
S. Bradner. IETF. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
M. Nilsson. IETF. The audio/mpeg Media Type. November 2000. Proposed Standard. URL: https://tools.ietf.org/html/rfc3003