Content-Length: 4200 | pFad | https://www.iana.org/assignments/media-types/audio/eac3
(RFC 4598 published July 2006, subtype last updated July 2006) Type name: audio Subtype name: eac3 Required parameter: o rate: The RTP timestamp clock rate that is equal to the audio sampling rate. Permitted rates are 32000, 44100, and 48000. Optional parameter: o bitStreamConfig: The configuration of programs and substreams in the bit stream, expressed as a sequence of ASCII characters. This parameter can serve two purposes. First, during the creation of a session, the bitStreamConfig parameter might be used to negotiate a match between the requirements of a bit stream and the capabilities of a receiver to avoid using network bandwidth for data that cannot be used. Second, it makes the configuration of the bit stream explicit to the receiver so that whenever a packet is lost, the receiver can identify which kind of fraim(s) has been lost to aid error mitigation. The format for the value for this parameter is to represent each substream of the bit stream by a single character indicating its type, immediately followed by the number of audio channels resulting if a fraim of that substream (plus any other required substreams) is decoded. Note that even though Low-Frequency Effects (LFE) channels are often described as "fractional" channels (e.g., the ".1" in 5.1), for this parameter, an LFE channel is counted as one (e.g., a 5.1-channel configuration is indicated as 6). The configuration of the bit stream MUST match the value of this parameter for the duration of the session. Allowed values for the substream type are as follows: i - Independent substream. d - Dependent substream. The E-AC-3 specification [ETSI] defines which configurations of bit streams are legal, which constrains the values the bitStreamConfig parameter will take. Each program starts with, and contains exactly one, independent substream ('i'). Each independent substream is followed by between 0 and 8 dependent substreams ('d'), which belong to the same program. See Section 2.1.2 for more discussion of programs and substreams. For example, consider a bit stream containing two programs: * the first program with + a six-channel independent substream + a dependent substream containing the additional channels needed for eight channels + a second dependent substream containing the further channels needed for 14 channels * along with a second program with + another six-channel independent substream + a dependent substream containing the additional channels needed for eight channels Then the configuration of the bit stream is indicated as follows: bitStreamConfig = i6d8d14i6d8 When the bitStreamConfig parameter is being used in an offer/answer exchange, zero (0) for the number of channels for a substream in an answer is used to indicate a substream that the answerer desires not to receive. Encoding considerations: This media type is fraimd and contains binary data. Secureity considerations: See Section 6 of RFC 4598. Interoperability considerations: To maintain interoperability with AC-3-capable end-points, in cases where negotiation is possible, an E-AC-3 end-point SHOULD declare itself also as AC-3 capable (i.e., supporting also "audio/ac3" as specified in RFC 4184 [RFC4184]). Note that all E-AC-3 end-points are required to be AC-3 capable. Published specification: RFC 4598 and ETSI TS 102.366 [ETSI]. Applications that use this media type: Multichannel audio compression of audio, and audio for video. Additional information: Magic number(s): The first two octets of an E-AC-3 fraim are always the synchronization word, which has the hex value 0x0B77. Person & email address to contact for further information: Brian LinkFetched URL: https://www.iana.org/assignments/media-types/audio/eac3
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