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Commit e26abfac authored by Ralph Giles's avatar Ralph Giles
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Update ISO Base Media Format draft to version 0.6.8.

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<b><u>Encapsulation of Opus in ISO Base Media File Format</u></b><br>
<font size="2">last updated: January 12, 2015</font><br>
<font size="2">last updated: April 28, 2016</font><br>
<br>
<div class="normal_link pre frame_box">
Encapsulation of Opus in ISO Base Media File Format
Version 0.6.6 (incomplete)
Version 0.6.8 (incomplete)
Table of Contents
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<a name="2"></a>
2 Normative References
[1] ISO/IEC 14496-12:2012 Corrected version
[1] ISO/IEC 14496-12:2015 Corrected version
Information technology — Coding of audio-visual objects — Part 12: ISO base media file format
[2] ISO/IEC 14496-12:2012/Amd.1:2013
Information technology — Coding of audio-visual objects — Part 12: ISO base media file format
AMENDMENT 1: Various enhancements including support for large metadata
[3] RFC 6716
[2] RFC 6716
Definition of the Opus Audio Codec
[4] draft-ietf-codec-oggopus-06
[3] draft-ietf-codec-oggopus-06
Ogg Encapsulation for the Opus Audio Codec
<a name="3"></a>
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The channelcount field shall be set to the sum of the total number of Opus bitstreams and the number
of Opus bitstreams producing two channels. This value is indentical with (M+N), where M is the value of
the *Coupled Stream Count* field and N is the value of the *Stream Count* field in the *Channel Mapping
Table* in the identification header defined in Ogg Opus [4].
Table* in the identification header defined in Ogg Opus [3].
+ samplesize:
The samplesize field shall be set to 16.
+ samplerate:
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The Opus Specific Box contains the Version field and this specification defines version 0 of this box.
If incompatible changes occured in the fields after the Version field within the OpusSpecificBox in the
future versions of this specification, another version will be defined.
This box refers to Ogg Opus [4] at many parts but all the data are stored as big-endian format.
This box refers to Ogg Opus [3] at many parts but all the data are stored as big-endian format.
The syntax and semantics of the Opus Specific Box is shown as follows.
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of those values, the reader shall not read the fields after this within the OpusSpecificBox.
+ OutputChannelCount:
The OutputChannelCount field shall be set to the same value as the *Output Channel Count* field in the
identification header defined in Ogg Opus [4].
identification header defined in Ogg Opus [3].
+ PreSkip:
The PreSkip field indicates the number of the priming samples, that is, the number of samples at 48000 Hz
to discard from the decoder output when starting playback. The value of the PreSkip field could be zero
when removing Opus samples containing the number of PCM samples equal to or more than of the priming
samples. The PreSkip field is not used for discarding the priming samples at the whole playback at all
since it is informative only, and that task falls on the Edit List Box.
to discard from the decoder output when starting playback. The value of the PreSkip field shall be at least
80 milliseconds' worth of PCM samples even when removing any number of Opus samples which may or may not
contain the priming samples. The PreSkip field is not used for discarding the priming samples at the whole
playback at all since it is informative only, and that task falls on the Edit List Box.
+ InputSampleRate:
The InputSampleRate field shall be set to the same value as the *Input Sample Rate* field in the
identification header defined in Ogg Opus [4].
identification header defined in Ogg Opus [3].
+ OutputGain:
The OutputGain field shall be set to the same value as the *Output Gain* field in the identification
header define in Ogg Opus [4]. Note that the value is stored as 8.8 fixed-point.
header define in Ogg Opus [3]. Note that the value is stored as 8.8 fixed-point.
+ ChannelMappingFamily:
The ChannelMappingFamily field shall be set to the same value as the *Channel Mapping Family* field in
the identification header defined in Ogg Opus [4].
the identification header defined in Ogg Opus [3].
+ StreamCount:
The StreamCount field shall be set to the same value as the *Stream Count* field in the identification
header defined in Ogg Opus [4].
header defined in Ogg Opus [3].
+ CoupledCount:
The CoupledCount field shall be set to the same value as the *Coupled Count* field in the identification
header defined in Ogg Opus [4].
header defined in Ogg Opus [3].
+ ChannelMapping:
The ChannelMapping field shall be set to the same octet string as *Channel Mapping* field in the identi-
fication header defined in Ogg Opus [4].
fication header defined in Ogg Opus [3].
4.3.3 Sample format<a name="4.3.3"></a>
An Opus sample is exactly one Opus packet for each of different Opus bitstreams. Due to support more than
two channels, an Opus sample can contain frames from multiple Opus bitstreams but all Opus packets shall
share with the total of frame sizes in a single Opus sample. The way of how to pack an Opus packet from
each of Opus bitstreams into a single Opus sample follows Appendix B. in RFC 6716 [3].
each of Opus bitstreams into a single Opus sample follows Appendix B. in RFC 6716 [2].
The endianness has nothing to do with any Opus sample since every Opus packet is processed byte-by-byte.
In this specification, 'sample' means 'Opus sample' except for 'padded samples', 'priming samples', 'valid
sample' and 'sample-accurate', i.e. 'sample' is 'sample' in the term defined in ISO/IEC 14496-12 [1].
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