xiph
/
opus
mirrorاز https://git.xiph.org/opus.git


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489490491492493494495496497498499500501502503504505506507508509510511512513514515516517518519520521522523524525526527528529530531532533534535536537538539540541542543544545546547548549550551552553554555556557558559560561562563564565566567568569570571572573574575576577578579580581582583584585586587588589590591592593594595596597598599600601602603604605606607608609610611612613614615616617618619620621622623624625626627628629630631632633634635636637638639640641642643644645646647648649650651652653654655656657658659660661662663664665666667668669670671672673674675676677678679680681682683684685686687688689690691692693694695696697698699700701702703704705706707708709710711712713714715716717718719720721722723724725726727728729730731732733734735736737738739740741742743744745746747748749750751752753754755756757758759760761762763764765766767768769770771772773774775776777778779780781782783784785786787788789790791792793794795796797798799800801802803804805806807808809810811812813
							<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
    <head>
        <link rel="stylesheet" type="text/css" href="opus_in_isobmff.css"/>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>Encapsulation of Opus in ISO Base Media File Format</title>
    </head>
    <body bgcolor="0x333333" text="#60B0C0">
        <b><u>Encapsulation of Opus in ISO Base Media File Format</u></b><br>
        <font size="2">last updated: October 1, 2014</font><br>
        <br>
        <div class="normal_link pre frame_box">

                                Encapsulation of Opus in ISO Base Media File Format
                                        Version 0.5.3 (incomplete)


Table of Contents
<a href="#1">1</a> Scope
<a href="#2">2</a> Normative References
<a href="#3">3</a> Terms and Definitions
<a href="#4">4</a> Design Rules of Encapsulation
    <a href="#4.1">4.1</a> File Type Indentification
    <a href="#4.2">4.2</a> Basic Structure
        <a href="#4.2.1">4.2.1</a> Initial Movie
        <a href="#4.2.2">4.2.2</a> Movie Fragments
    <a href="#4.3">4.3</a> Byte Order
    <a href="#4.4">4.4</a> Definition of Opus sample
        <a href="#4.4.1">4.4.1</a> Opus sample
        <a href="#4.4.2">4.4.2</a> Duration of Opus sample
        <a href="#4.4.3">4.4.3</a> Sub-sample
    <a href="#4.5">4.5</a> Random Access
        <a href="#4.5.1">4.5.1</a> Random Access Point
        <a href="#4.5.2">4.5.2</a> Pre-roll
    <a href="#4.6">4.6</a> Trimming of Actual Duration
    <a href="#4.7">4.7</a> Channel Layout
    <a href="#4.8">4.8</a> Additional Requirements, Restrictions, Recommendations and Definitions for Boxes
        <a href="#4.8.1">4.8.1</a> File Type Box
        <a href="#4.8.2">4.8.2</a> Segment Type Box
        <a href="#4.8.3">4.8.3</a> Movie Header Box
        <a href="#4.8.4">4.8.4</a> Track Header Box
        <a href="#4.8.5">4.8.5</a> Edit Box
        <a href="#4.8.6">4.8.6</a> Edit List Box
        <a href="#4.8.7">4.8.7</a> Media Header Box
        <a href="#4.8.8">4.8.8</a> Handler Reference Box
        <a href="#4.8.9">4.8.9</a> Sound Media Header Box
        <a href="#4.8.10">4.8.10</a> Sample Table Box
        <a href="#4.8.11">4.8.11</a> OpusSampleEntry
        <a href="#4.8.12">4.8.12</a> Opus Specific Box
        <a href="#4.8.13">4.8.13</a> Sample Group Description Box
        <a href="#4.8.14">4.8.14</a> Sample to Group Box
        <a href="#4.8.15">4.8.15</a> Track Extends Box
        <a href="#4.8.16">4.8.16</a> Track Fragment Box
        <a href="#4.8.17">4.8.17</a> Track Fragment Header Box
        <a href="#4.8.18">4.8.18</a> Track Fragment Run Box
    <a href="#4.9">4.9</a> Example of Encapsulation
<a href="#5">5</a> Author's Address

<a name="1"></a>
1 Scope
    This specification specifies the fundamental way of the encapsulation of Opus coded bitstreams in ISO Base Media
    file formats and its derivatives.

<a name="2"></a>
2 Normative References
    [1] ISO/IEC 14496-12:2012 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
        Definition of the Opus Audio Codec

    [4] draft-ietf-codec-oggopus-04
        Ogg Encapsulation for the Opus Audio Codec

<a name="3"></a>
3 Terms and Definitions
    3.1 active track
        enabled track from the non-alternate group or selected track from alternate group
        TODO: For alternate group, how about handling of disabled tracks?
              Some implementations treat disabled tracks in alternate group as a non-default track.
              Under the such implementations, the selected track behaves as an enabled track.
              Should we define the implementation in this specification?
              Or leave it as implementation-defined?

    3.2 actual duration
        duration constructed from valid samples

    3.3 edit
        entry in the Edit List Box

    3.4 padded samples
        PCM samples after decoding Opus sample(s) which are not valid samples
        An Opus bitstream always contains them partially at the beginning and may contain them in part at the end, as
        long as not physically removed yet at the beginning and/or the end.

    3.5 priming samples
        padded samples at the beginning of the Opus bitstream

    3.6 sample-accurate
        for any PCM sample, a timestamp exactly matching its sampling timestamp is present in the media timeline.

    3.7 valid samples
        PCM samples after decoding Opus sample(s) corresponding to input PCM samples

<a name="4"></a>
4 Design Rules of Encapsulation
    4.1 File Type Indentification<a name="4.1"></a>
        This specification does not define any brand to declare files are conformant to this specification.
        TODO: Should we define such brands, e.g. 'Opus'? If we define the brand(s), we can utilize files conformant to
              this specification for the storage of Opus coded bitstreams without other derived file formats.
              It is not preferable that encapsulation of Opus bitstreams with only the brands of the ISO Base Media File
              Format, though files conformant to this specification are compatible with certain versions of the ISO
              Base Media File Format. See ISO/IEC 14496-12 [3] E.1 Introduction.
              If you desire that this file format is an alternative file format to the Ogg Opus, I recommend you define.
<a name="4.2"></a>
    4.2 Basic Structure
        4.2.1 Initial Movie<a name="4.2.1"></a>
            This subclause specifies a basic structure of the Movie Box as follows:

            +----+----+----+----+----+----+----+----+------------------------------+
            |moov|    |    |    |    |    |    |    | Movie Box                    |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |mvhd|    |    |    |    |    |    | Movie Header Box             |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |trak|    |    |    |    |    |    | Track Box                    |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |tkhd|    |    |    |    |    | Track Header Box             |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |edts|    |    |    |    |    | Edit Box                     |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |elst|    |    |    |    | Edit List Box                |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |mdia|    |    |    |    |    | Media Box                    |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |mdhd|    |    |    |    | Media Header Box             |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |hdlr|    |    |    |    | Handler Reference Box        |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |minf|    |    |    |    | Media Information Box        |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |smhd|    |    |    | Sound Media Information Box  |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |dinf|    |    |    | Data Information Box         |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |dref|    |    | Data Reference Box           |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |    |url |    | DataEntryUrlBox              |
            +----+----+----+----+----+----+ or +----+------------------------------+
            |    |    |    |    |    |    |urn |    | DataEntryUrnBox              |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |stbl|    |    |    | Sample Table                 |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |stsd|    |    | Sample Description Box       |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |    |Opus|    | OpusSampleEntry              |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |    |    |dOps| Opus Specific Box            |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |stts|    |    | Decoding Time to Sample Box  |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |stsc|    |    | Sample To Chunk Box          |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |stsz|    |    | Sample Size Box              |
            +----+----+----+----+----+ or +----+----+------------------------------+
            |    |    |    |    |    |stz2|    |    | Compact Sample Size Box      |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |stco|    |    | Chunk Offset Box             |
            +----+----+----+----+----+ or +----+----+------------------------------+
            |    |    |    |    |    |co64|    |    | Chunk Large Offset Box       |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |sgpd|    |    | Sample Group Description Box |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |    |    |    |sbgp|    |    | Sample to Group Box          |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |mvex|*   |    |    |    |    |    | Movie Extends Box            |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |trex|*   |    |    |    |    | Track Extends Box            |
            +----+----+----+----+----+----+----+----+------------------------------+

                    Figure 1 - Basic structure of Movie Box

            It is strongly recommended that the order of boxes should follow the above structure.
            Boxes marked with an asterisk (*) may be present.
            For some boxes listed above, the additional requirements, restrictions, recommendations and definitions
            are specified in 4.8 Additional Requirements, Restrictions, Recommendations and Definitions for Boxes in
            this specification. For the others, the definition is as is defined in ISO/IEC 14496-12 [1].

        4.2.2 Movie Fragments<a name="4.2.2"></a>
            This subclause specifies a basic structure of the Movie Fragment Box as follows:

            +----+----+----+----+----+----+----+----+------------------------------+
            |moof|    |    |    |    |    |    |    | Movie Fragment Box           |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |mfhd|    |    |    |    |    |    | Movie Fragment Header Box    |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |traf|    |    |    |    |    |    | Track Fragment Box           |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |tfhd|    |    |    |    |    | Track Fragment Header Box    |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |trun|    |    |    |    |    | Track Fragment Run Box       |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |sgpd|*   |    |    |    |    | Sample Group Description Box |
            +----+----+----+----+----+----+----+----+------------------------------+
            |    |    |sbgp|*   |    |    |    |    | Sample to Group Box          |
            +----+----+----+----+----+----+----+----+------------------------------+

                    Figure 2 - Basic structure of Movie Fragment Box

            It is strongly recommended that the Movie Fragment Header Box and the Track Fragment Header Box be
            placed first in their container.
            Boxes marked with an asterisk (*) may be present.
            For some boxes listed above, the additional requirements, restrictions, recommendations and definitions
            are specified in 4.8 Additional Requirements, Restrictions, Recommendations and Definitions for Boxes in
            this specification. For the others, the definition is as is defined in ISO/IEC 14496-12 [1].
<a name="4.3"></a>
    4.3 Byte Order
        The fields in the boxes are stored as big-endian format.
        All Opus samples are processed byte-by-byte. Therefore, the endianness has nothing to do with any Opus sample.
<a name="4.4"></a>
    4.4 Definition of Opus sample
        4.4.1 Opus sample<a name="4.4.1"></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].
            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].

                +-----------------------------------------+-------------------------------------+
                | Opus packet 0 (self-delimiting framing) | Opus packet 1 (undelimited framing) |
                +-----------------------------------------+-------------------------------------+
                |<---------------------------- the size of Opus sample ------------------------>|

                    Figure 3 - Example structure of an Opus sample containing two Opus bitstreams

        4.4.2 Duration of Opus sample<a name="4.4.2"></a>
            The duration of Opus sample is given by multiplying the total of frame sizes for a single Opus bitstream
            expressed in seconds by the value of the timescale field in the Media Header Box.
            Let's say an Opus sample consists of two Opus bitstreams, where the frame size of one bitstream is 40 milli-
            seconds and the frame size of another is 60 milliseconds, and the timescale field in the Media Header Box
            is set to 48000, then the duration of that Opus sample shall be 120 milliseconds since three 40 millisecond
            frame and two 60 millisecond frames shall be contained because of the maximum duration of Opus packet, 120
            milliseconds, and 5760 in the timescale indicated in the Media Header Box.

            To indicate the valid samples excluding the padded samples at the end of Opus bitstream, the duration of
            the last Opus sample of an Opus bitstream is given by multiplying the number of the valid samples by the
            value produced by dividing the value of the timescale field in the Media Header Box by 48000.

        4.4.3 Sub-sample<a name="4.4.3"></a>
            The structure of the last Opus packet in an Opus sample is different from the others in the same Opus sample,
            and the others are invalid Opus packets as an Opus sample because of self-delimiting framing. To avoid
            complexities, sub-sample is not defined for Opus sample in this specification.
<a name="4.5"></a>
    4.5 Random Access
        4.5.1 Random Access Point<a name="4.5.1"></a>
            All Opus samples can be independently decoded i.e. every Opus sample is a sync sample. Therefore, the Sync
            Sample Box shall not be present as long as there are no samples other than Opus samples in the same track.

        4.5.2 Pre-roll<a name="4.5.2"></a>
            Opus requires at least 80 millisecond pre-roll after each random access.
            Pre-roll is indicated by the roll_distance field in AudioRollRecoveryEntry. AudioPreRollEntry shall not be
            used since every Opus sample is a sync sample in Opus bitstream. Note that roll_distance is expressed in
            sample units in a term of ISO Base Media File Format, and always takes negative values.

            For the requirement of AudioRollRecoveryEntry, the compatible_brands field in the File Type Box and/or
            the Segment Type Box shall contain at least one brand which requires support for roll groups. See also
            4.8.1 File Type Box and 4.8.2 Segment Type Box in this specification.
<a name="4.6"></a>
    4.6 Trimming of Actual Duration
        Due to the priming samples (or the padding at the beginning) derived from the pre-roll for the startup and the
        padded samples at the end, we need trim from media to get the actual duration. An edit in the Edit List Box can
        achieve this demand.
        For sample-accurate trimming, proper timescale should be set to the timescale field in the Movie Header Box
        and the Media Header Box inside Track Box(es) for Opus bitstream.

        The Edit List Box is applied to whole movie including all movie fragments. Therefore, it is impossible to tell
        the actual duration in the case producing movie fragments on the fly such as live-streaming. In such cases,
        the duration of the last Opus sample may be helpful.
        TODO: Should we define a new box which indicates the last Opus samples?
              Since this specification allows multiple sample descriptions, i.e. allows concatenation of multiple Opus
              bitstreams in a track, each Opus bitstream may contain some padded samples.
              Without such a box, we cannot know in container level whether an Opus sample is the last Opus sample in
              an Opus bitstream or not. Is this preferable?

        See also 4.8.6 Edit List Box in this specification.
<a name="4.7"></a>
    4.7 Channel Layout
        By the application of alternate_group in the Track Header Box, whole audio channels in all active tracks from
        non-alternate group and/or different alternate group from each other are composited into the presentation. If
        an Opus sample consists of multiple Opus bitstreams, it can be splitted into individual Opus bitstreams and
        reconstructed into new Opus samples as long as every Opus bitstream has the same total duration in each Opus
        sample. This nature can be utilized to encapsulate a single Opus bitstream in each track without breaking the
        original channel layout.

        As an example, let's say there is a following track:
            OutputChannelCount = 6;
            StreamCount        = 4;
            CoupledCount       = 2;
            ChannelMapping     = {0, 1, 2, 3, 4, 5}; // front left, front center, front right, rear left, rear right, LFE
        You extract the four Opus bitstreams from this track and you encapsulate two of the four into a track and the
        others into another track. The former track is as follows.
            OutputChannelCount = 6;
            StreamCount        = 2;
            CoupledCount       = 2;
            ChannelMapping     = {0, 255, 1, 2, 3, 255}; // front left, front center, front right, rear left, rear right, LFE
        And the latter track is as follows.
            OutputChannelCount = 6;
            StreamCount        = 2;
            CoupledCount       = 0;
            ChannelMapping     = {255, 0, 255, 255, 255, 1}; // front left, front center, front right, rear left, rear right, LFE
        In addition, the value of the alternate_group field in the both tracks is set to 0. As the result, the player
        may play as if channels with 255 are not present, and play the presentation constructed from the both tracks
        in the same channel layout as the one of the original track. Keep in mind that the way of the composition, i.e.
        the mixing for playback, is not defined here, and maybe different results could occur except for the channel
        layout of the original, depending on an implementation or the definition of a derived file format.

        Note that some derived file formats may specify the restriction to ignore alternate grouping. In the context of
        such file formats, this application is not available. This unavailability does not mean incompatibilities among
        file formats unless the restriction to the value of the alternate_group field is specified and brings about
        any conflict among their definitions.

        TODO: The future amendments of ISO/IEC 14496-12 [1] will add further supports of channel layouts and it may be
              able to exclude certain channels from the already mapped channels to remove pure silent channels. The
              channel mapping defined in the Opus Specific Box should be designed as processed before the extensions,
              and the extensions should be placed after the Opus Specific Box.
<a name="4.8"></a>
    4.8 Additional Requirements, Restrictions, Recommendations and Definitions for Boxes
        4.8.1 File Type Box<a name="4.8.1"></a>
            For any track containing Opus bitstreams, the following requirements are applied.
            + compatible_brands:
                The compatible_brands fields shall contain at least one brand which requires support for the structural
                boxes listed at 4.2 Basic Structure, and the additional requirements, restrictions, recommendations and
                definitions specified in 4.8 Additional Requirements, Restrictions, Recommendations and Definitions for
                Boxes in this specification.
                As an example, the minimal support of the encapsulation of Opus bitstreams in ISO Base Media file format
                requires the 'iso2' brand since support of roll groups is required.

        4.8.2 Segment Type Box<a name="4.8.2"></a>
            The same requirements are applied as specified at 4.8.1 File Type Box in this specification.

        4.8.3 Movie Header Box<a name="4.8.3"></a>
            If any track containing Opus bitstreams, the following recommendations are applied.
            + timescale:
                The timescale field should be set to the same value of the timescale field in the Media Header Box
                inside Track Box(es) for Opus bitstream if no tracks for bitstreams other than Opus bitstream is present.

        4.8.4 Track Header Box<a name="4.8.4"></a>
            For any track containing Opus bitstreams, the following requirements are applied.
            + layer:
                The layer field shall be set to 0.
            + matrix:
                The matrix field shall be set to { 0x00010000,0,0,0,0x00010000,0,0,0,0x40000000 }.
            + width:
                The width field shall be set to 0.
            + height:
                The height field shall be set to 0.

        4.8.5 Edit Box<a name="4.8.5"></a>
            For any track containing Opus bitstreams, exactly one Edit Box shall be present.

        4.8.6 Edit List Box<a name="4.8.6"></a>
            For any track containing Opus bitstreams, exactly one Edit List Box shall be present. In addition, for
            non-empty edits, the following recommendations are applied.
            + segment_duration:
                The segment_duration field can be used to indicate the actual duration of Opus bitstream.
                When the value of the timescale field in the Movie Header Box is equal to 48000, the segment_duration
                field shall be set to the number of the valid samples to indicate the actual duration.
                When enabling movie fragments, the segment_duration field may be set to 0. The value 0 represents
                implicit duration equal to the sum of the duration of all samples. This would be helpful for excluding
                the padded samples from the presentation timeline when producing movie fragments on the fly.
            + media_time:
                The media_time field can be used to remove the priming samples of Opus bitstreams.
                When the value of the timescale field in the Media Header Box is equal to 48000, the media_time field
                shall be set to the number of the priming samples to remove the priming samples.
            + media_rate:
                If the segment_duration field is used to indicate the actual duration, the media_rate field shall be
                set to 1.

        4.8.7 Media Header Box<a name="4.8.7"></a>
            For any track containing Opus bitstreams, the following recommendation is applied.
            + timescale:
                The timescale field should be set to 48000 to access sample-accurately.

        4.8.8 Handler Reference Box<a name="4.8.8"></a>
            For any track containing Opus bitstreams, the following requirement is applied.
            + handler_type:
                The handler_type field shall be set to 'soun'.

        4.8.9 Sound Media Header Box<a name="4.8.9"></a>
            For any track containing Opus bitstreams, the Sound Media Header Box shall be present.

        4.8.10 Sample Table Box<a name="4.8.10"></a>
            For any track containing Opus bitstreams, at least one Sample Group Description Boxes and at least one
            Sample to Group Boxes shall be present, and the Sync Sample Box shall not be present as long as there are
            no samples other than Opus samples in the same track.

        4.8.11 OpusSampleEntry<a name="4.8.11"></a>
            For any track containing Opus bitstreams, at least one OpusSampleEntry shall be present.

            The syntax and semantics of the OpusSampleEntry is shown as follows.

            class OpusSampleEntry() extends AudioSampleEntry ('Opus'){
                OpusSpecificBox();
            }

            + channelcount:
                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].
            + samplesize:
                The samplesize field shall be set to 16.
            + samplerate:
                The samplerate field shall be set to 48000&lt&lt16.

        4.8.12 Opus Specific Box<a name="4.8.12"></a>
            Exactly one Opus Specific Box shall be present in each OpusSampleEntry.
            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.

            The syntax and semantics of the Opus Specific Box is shown as follows.

            class ChannelMappingTable (unsigned int(8) OutputChannelCount){
                unsigned int(8) StreamCount;
                unsigned int(8) CoupledCount;
                unsigned int(8 * OutputChannelCount) ChannelMapping;
            }

            aligned(8) class OpusSpecificBox extends FullBox('dOps', version, dflags){
                unsigned int(8) OutputChannelCount;
                if (dflags & 0x000001) {
                    unsigned int(16) PreSkip;
                }
                if (dflags & 0x000002) {
                    unsigned int(32) InputSampleRate;
                }
                if (dflags & 0x000004) {
                    signed int(16) OutputGain;
                }
                unsigned int(8) ChannelMappingFamily;
                if (ChannelMappingFamily != 0) {
                    ChannelMappingTable(OutputChannelCount);
                }
            }

            + version:
                The version field shall be set to 0.
                In the future versions of this specification, this field may be set to other values. And without support
                of those values, the reader shall not read the fields after this within the OpusSpecificBox.
            + flags:
                The following flags are defined in the dflags:
                    0x000001 pre-skip-present:
                        This flag indicates the presence of the PreSkip field.
                    0x000002 input-sample-rate-present:
                        This flag indicates the presence of the InputSampleRate field.
                    0x000004 output-gain-present:
                        This flag indicates the presence of the OutputGain field.
            + 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].
            + PreSkip:
                The PreSkip field shall be set to the same value as the *Pre-skip* field in the identification header
                defined in Ogg Opus [4]. Note that the value is stored as big-endian format.
                The PreSkip field can be absent after removing Opus samples containing the number of PCM samples more
                than of the priming samples.
                The PreSkip field is not used for removing 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]. Note that the value is stored as big-endian format.
                If the InputSampleRate field is absent, process as if it is set to 0, which indicates "unspecified".
            + 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 and big-endian format.
                If the OutputGain field is absent, process as if it is set to 0.
            + 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].
            + 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].
            + 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].
            + 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].

        4.8.13 Sample Group Description Box<a name="4.8.13"></a>
            For any track containing Opus bitstreams, at least one Sample Group Description Box shall be present and have
            the grouping_type field set to 'roll'. In addition, the following requirements and restriction are applied.
            + version:
                The version field shall be set to 1 if the grouping_type field set to 'roll'.
            + default_length
                The default_length field shall be set to 2 if the grouping_type field set to 'roll'.
            + roll_distance:
                The roll_distance field in any AudioRollRecoveryEntry shall not be set to zero and positive values for
                any Opus sample.

            See also 4.5.2 Pre-roll.

        4.8.14 Sample to Group Box<a name="4.8.14"></a>
            For any track containing Opus bitstreams, at least one Sample to Group Box shall be present and have the
            grouping_type field set to 'roll'. In addition, the following requirement is applied.
            + group_description_index:
                The group_description_index fields shall not be set to 0 if the grouping_type field set to 'roll'.

        4.8.15 Track Extends Box<a name="4.8.15"></a>
            For any track containing Opus bitstreams, the following requirement is applied.
            + default_sample_flags:
                The sample_is_non_sync_sample field shall be set to 0.

        4.8.16 Track Fragment Box<a name="4.8.16"></a>
            For any track containing Opus bitstreams, if any sample is contained in track fragment, the Sample to
            Group Box with the grouping_type field set to 'roll' shall be present for that track fragment.

        4.8.17 Track Fragment Header Box<a name="4.8.17"></a>
            For any track containing Opus bitstreams, the following requirement is applied.
            + default_sample_flags:
                The sample_is_non_sync_sample field shall be set to 0.

        4.8.18 Track Fragment Run Box<a name="4.8.18"></a>
            For any track containing Opus bitstreams, the following requirements are applied.
            + first_sample_flags:
                The sample_is_non_sync_sample field shall be set to 0.
            + sample_flags:
                The sample_is_non_sync_sample field shall be set to 0.
<a name="4.9"></a>
    4.9 Example of Encapsulation
        [File]
            size = 10349
            [ftyp: File Type Box]
                position = 0
                size = 24
                major_brand = mp42 : MP4 version 2
                minor_version = 0
                compatible_brands
                    brand[0] = mp42 : MP4 version 2
                    brand[1] = iso2 : ISO Base Media file format version 2
            [free: Free Space Box]
                position = 24
                size = 8
            [mdat: Media Data Box]
                position = 32
                size = 9551
            [moov: Movie Box]
                position = 9583
                size = 766
                [mvhd: Movie Header Box]
                    position = 9591
                    size = 108
                    version = 0
                    flags = 0x000000
                    creation_time = UTC 2014/09/23, 15:23:21
                    modification_time = UTC 2014/09/23, 15:23:21
                    timescale = 48000
                    duration = 33600 (00:00:00.700)
                    rate = 1.000000
                    volume = 1.000000
                    reserved = 0x0000
                    reserved = 0x00000000
                    reserved = 0x00000000
                    transformation matrix
                        | a, b, u |   | 1.000000, 0.000000, 0.000000 |
                        | c, d, v | = | 0.000000, 1.000000, 0.000000 |
                        | x, y, w |   | 0.000000, 0.000000, 1.000000 |
                    pre_defined = 0x00000000
                    pre_defined = 0x00000000
                    pre_defined = 0x00000000
                    pre_defined = 0x00000000
                    pre_defined = 0x00000000
                    pre_defined = 0x00000000
                    next_track_ID = 2
                [iods: Object Descriptor Box]
                    position = 9699
                    size = 33
                    version = 0
                    flags = 0x000000
                    [tag = 0x10: MP4_IOD]
                        expandableClassSize = 16
                        ObjectDescriptorID = 1
                        URL_Flag = 0
                        includeInlineProfileLevelFlag = 0
                        reserved = 0xf
                        ODProfileLevelIndication = 0xff
                        sceneProfileLevelIndication = 0xff
                        audioProfileLevelIndication = 0xfe
                        visualProfileLevelIndication = 0xff
                        graphicsProfileLevelIndication = 0xff
                        [tag = 0x0e: ES_ID_Inc]
                            expandableClassSize = 4
                            Track_ID = 1
                [trak: Track Box]
                    position = 9732
                    size = 617
                    [tkhd: Track Header Box]
                        position = 9740
                        size = 92
                        version = 0
                        flags = 0x000007
                            Track enabled
                            Track in movie
                            Track in preview
                        creation_time = UTC 2014/09/23, 15:23:21
                        modification_time = UTC 2014/09/23, 15:23:21
                        track_ID = 1
                        reserved = 0x00000000
                        duration = 33600 (00:00:00.700)
                        reserved = 0x00000000
                        reserved = 0x00000000
                        layer = 0
                        alternate_group = 0
                        volume = 1.000000
                        reserved = 0x0000
                        transformation matrix
                            | a, b, u |   | 1.000000, 0.000000, 0.000000 |
                            | c, d, v | = | 0.000000, 1.000000, 0.000000 |
                            | x, y, w |   | 0.000000, 0.000000, 1.000000 |
                        width = 0.000000
                        height = 0.000000
                    [edts: Edit Box]
                        position = 9832
                        size = 36
                        [elst: Edit List Box]
                            position = 9840
                            size = 28
                            version = 0
                            flags = 0x000000
                            entry_count = 1
                            entry[0]
                                segment_duration = 33600
                                media_time = 3840
                                media_rate = 1.000000
                    [mdia: Media Box]
                        position = 9868
                        size = 481
                        [mdhd: Media Header Box]
                            position = 9876
                            size = 32
                            version = 0
                            flags = 0x000000
                            creation_time = UTC 2014/09/23, 15:23:21
                            modification_time = UTC 2014/09/23, 15:23:21
                            timescale = 48000
                            duration = 38400 (00:00:00.800)
                            language = und
                            pre_defined = 0x0000
                        [hdlr: Handler Reference Box]
                            position = 9908
                            size = 51
                            version = 0
                            flags = 0x000000
                            pre_defined = 0x00000000
                            handler_type = soun
                            reserved = 0x00000000
                            reserved = 0x00000000
                            reserved = 0x00000000
                            name = Xiph Audio Handler
                        [minf: Media Information Box]
                            position = 9959
                            size = 390
                            [smhd: Sound Media Header Box]
                                position = 9967
                                size = 16
                                version = 0
                                flags = 0x000000
                                balance = 0.000000
                                reserved = 0x0000
                            [dinf: Data Information Box]
                                position = 9983
                                size = 36
                                [dref: Data Reference Box]
                                    position = 9991
                                    size = 28
                                    version = 0
                                    flags = 0x000000
                                    entry_count = 1
                                    [url : Data Entry Url Box]
                                        position = 10007
                                        size = 12
                                        version = 0
                                        flags = 0x000001
                                        location = in the same file
                            [stbl: Sample Table Box]
                                position = 10019
                                size = 330
                                [stsd: Sample Description Box]
                                    position = 10027
                                    size = 72
                                    version = 0
                                    flags = 0x000000
                                    entry_count = 1
                                    [Opus: Audio Description]
                                        position = 10043
                                        size = 56
                                        reserved = 0x000000000000
                                        data_reference_index = 1
                                        reserved = 0x0000
                                        reserved = 0x0000
                                        reserved = 0x00000000
                                        channelcount = 2
                                        samplesize = 16
                                        pre_defined = 0
                                        reserved = 0
                                        samplerate = 48000.000000
                                        [dOps: Opus Specific Box]
                                            position = 10071
                                            size = 20
                                            version = 0
                                            flags = 0x000006
                                            OutputChannelCount = 2
                                            InputSampleRate = 44100
                                            OutputGain = 0.000000
                                            ChannelMappingFamily = 0
                                [stts: Decoding Time to Sample Box]
                                    position = 10099
                                    size = 24
                                    version = 0
                                    flags = 0x000000
                                    entry_count = 1
                                    entry[0]
                                        sample_count = 10
                                        sample_delta = 3840
                                [stsc: Sample To Chunk Box]
                                    position = 10123
                                    size = 40
                                    version = 0
                                    flags = 0x000000
                                    entry_count = 2
                                    entry[0]
                                        first_chunk = 1
                                        samples_per_chunk = 4
                                        sample_description_index = 1
                                    entry[1]
                                        first_chunk = 3
                                        samples_per_chunk = 2
                                        sample_description_index = 1
                                [stsz: Sample Size Box]
                                    position = 10163
                                    size = 60
                                    version = 0
                                    flags = 0x000000
                                    sample_size = 0 (variable)
                                    sample_count = 10
                                    entry_size[0] = 780
                                    entry_size[1] = 920
                                    entry_size[2] = 963
                                    entry_size[3] = 988
                                    entry_size[4] = 1024
                                    entry_size[5] = 951
                                    entry_size[6] = 933
                                    entry_size[7] = 1017
                                    entry_size[8] = 992
                                    entry_size[9] = 975
                                [stco: Chunk Offset Box]
                                    position = 10223
                                    size = 28
                                    version = 0
                                    flags = 0x000000
                                    entry_count = 3
                                    chunk_offset[0] = 40
                                    chunk_offset[1] = 3691
                                    chunk_offset[2] = 7616
                                [sgpd: Sample Group Description Box]
                                    position = 10251
                                    size = 30
                                    version = 1
                                    flags = 0x000000
                                    grouping_type = roll
                                    default_length = 2 (constant)
                                    entry_count = 3
                                    roll_distance[0] = -1
                                    roll_distance[1] = -2
                                    roll_distance[2] = -3
                                [sbgp: Sample to Group Box]
                                    position = 10281
                                    size = 68
                                    version = 0
                                    flags = 0x000000
                                    grouping_type = roll
                                    entry_count = 6
                                    entry[0]
                                        sample_count = 2
                                        group_description_index = 1
                                    entry[1]
                                        sample_count = 1
                                        group_description_index = 2
                                    entry[2]
                                        sample_count = 1
                                        group_description_index = 3
                                    entry[3]
                                        sample_count = 1
                                        group_description_index = 2
                                    entry[4]
                                        sample_count = 3
                                        group_description_index = 3
                                    entry[5]
                                        sample_count = 2
                                        group_description_index = 1

<a name="5"></a>
5 Authors' Address
    Yusuke Nakamura
        Email: muken.the.vfrmaniac |at| gmail.com
        </div>
    </body>
</html>