Commit fdc6d3cc authored by Ralph Giles's avatar Ralph Giles
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Update ISO Base Media Format draft to version 0.6.6.

parent af68b857
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<b><u>Encapsulation of Opus in ISO Base Media File Format</u></b><br>
<font size="2">last updated: December 13, 2014</font><br>
<font size="2">last updated: January 12, 2015</font><br>
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Encapsulation of Opus in ISO Base Media File Format
Version 0.6.2 (incomplete)
Version 0.6.6 (incomplete)
Table of Contents
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1 Scope
This specification specifies the fundamental way of the encapsulation of Opus coded bitstreams in ISO Base Media
file formats and its derivatives.
file format and its derivatives. The encapsulation of Opus coded bitstreams in QuickTime file format is outside
the scope of this specification.
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2 Normative References
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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
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requirements described in this clause without contradiction, in the compatible brands list of the File Type Box.
As an example, the minimal support of the encapsulation of Opus bitstreams in ISO Base Media file format requires
the 'iso2' brand in the compatible brands list since support of roll groups is required.
TODO: Should we define specific 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.
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4.2 Overview of Track Structure
This clause summarizes requirements of the encapsulation of Opus coded bitstream as media data in audio tracks
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+ The handler_type field in the Handler Reference Box shall be set to 'soun'.
+ The Media Information Box shall contain the Sound Media Header Box.
+ The codingname of the sample entry is 'Opus'.
This specification does not define any encapsulation using MP4AudioSampleEntry with objectTypeIndication
specified by the MPEG-4 Registration Authority (
See 4.3.1 Sample entry format to get the details about the sample entry.
+ The 'dOps' box is added to the sample entry to convey initializing information for the decoder.
See 4.3.2 Opus Specific Box to get the details.
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|<---------------------------- the size of Opus sample ------------------------>|
Figure 3 - Example structure of an Opus sample containing two Opus bitstreams
Figure 1 - Example structure of an Opus sample containing two Opus bitstreams
4.3.4 Duration of Opus sample<a name="4.3.4"></a>
The duration of Opus sample is given by multiplying the total of frame sizes for a single Opus bitstream
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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 by setting zero to the segment_duration field since the
value 0 represents implicit duration equal to the sum of the duration of all samples.
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?
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4.5 Channel Layout (informative)
By the application of alternate_group in the Track Header Box, whole audio channels in all active tracks from
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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.
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4.6 Basic Structure (informative)
4.6.1 Initial Movie<a name="4.6.1"></a>
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| | |trex|* | | | | | Track Extends Box |
Figure 1 - Basic structure of Movie Box
Figure 2 - 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.
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| | |sbgp|* | | | | | Sample to Group Box |
Figure 2 - Basic structure of Movie Fragment Box
Figure 3 - 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.
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