Encapsulation of Opus in ISO Base Media File Format

+ + Encapsulation of Opus in ISO Base Media File Format + Version 0.8.1 (incomplete) + + +Table of Contents +1 Scope +2 Normative References +3 Terms and Definitions +4 Design Rules of Encapsulation + 4.1 File Type Identification + 4.2 Overview of Track Structure + 4.3 Definitions of Opus sample + 4.3.1 Sample entry format + 4.3.2 Opus Specific Box + 4.3.3 Sample format + 4.3.4 Duration of Opus sample + 4.3.5 Sub-sample + 4.3.6 Random Access + 4.3.6.1 Random Access Point + 4.3.6.2 Pre-roll + 4.4 Trimming of Actual Duration + 4.5 Channel Mapping + 4.5.1 ISO Base Media native Channel Mapping + 4.5.2 Composition on all active tracks (informative) + 4.6 Basic Structure (informative) + 4.6.2 Initial Movie + 4.6.3 Movie Fragments + 4.7 Example of Encapsulation (informative) +5 Author's Address + + +1 Scope + This specification specifies the fundamental way of the encapsulation of Opus coded bitstreams in ISO Base Media + file format and its derivatives. The encapsulation of Opus coded bitstreams in QuickTime file format is outside + the scope of this specification. + + +2 Normative References + [1] ISO/IEC 14496-12:2015 Corrected version + Information technology — Coding of audio-visual objects — Part 12: ISO base media file format + + [2] RFC 6716 + Definition of the Opus Audio Codec + + [3] RFC 7845 + Ogg Encapsulation for the Opus Audio Codec + + +3 Terms and Definitions + 3.1 active track + enabled track from the non-alternate group or selected track from alternate group + + 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 + + +4 Design Rules of Encapsulation + 4.1 File Type Identification + This specification defines the brand 'Opus' to declare files are conformant to this specification. Additionally, + files conformant to this specification shall contain at least one brand, which supports the requirements and the + 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. + + 4.2 Overview of Track Structure + This clause summarizes requirements of the encapsulation of Opus coded bitstream as media data in audio tracks + in file formats compliant with the ISO Base Media File Format. The details are described in clauses after this + clause. + + 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 (http://www.mp4ra.org/). + 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. + + An Opus sample is exactly one Opus packet for each of different Opus bitstreams. + See 4.3.3 Sample format to get the details. + + Every Opus sample is a sync sample but requires pre-roll for every random access to get correct output. + See 4.3.6 Random Access to get the details. + + 4.3 Definitions of Opus sample + 4.3.1 Sample entry format + For any track containing Opus bitstreams, at least one sample entry describing corresponding Opus bitstream + shall be present inside the Sample Table Box. This version of the specification defines only one sample + entry format named OpusSampleEntry whose codingname is 'Opus'. This sample entry includes exactly one Opus + Specific Box defined in 4.3.2 as a mandatory box and indicates that Opus samples described by this sample + entry are stored by the sample format described in 4.3.3. + + The syntax and semantics of the OpusSampleEntry is shown as follows. + + class OpusSampleEntry() extends AudioSampleEntry ('Opus') { + OpusSpecificBox(); + } + + + channelcount: + The channelcount field indicates the number of output channels and shall be set to the same value of + the OutputChannelCount in the OpusDecoderConfigurationRecord. The value of this field may be used in + the ChannelLayout if any as described in 4.5.1. + + samplesize: + The samplesize field shall be set to 16. + + samplerate: + The samplerate field shall be set to 48000<<16. + + OpusSpecificBox + This box contains initializing information for the decoder as defined in 4.3.2. + + 4.3.2 Opus Specific Box + Exactly one Opus Specific Box shall be present in each OpusSampleEntry. + The Opus Specific Box contains an OpusDecoderConfigurationRecord which contains the Version field and + this specification defines version 0 of this record. If incompatible changes occured in the fields after + the Version field within the OpusDecoderConfigurationRecord in the future versions of this specification, + another version will be defined. + 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. + + class ChannelMappingTable (unsigned int(8) OutputChannelCount) { + unsigned int(8) StreamCount; + unsigned int(8) CoupledCount; + unsigned int(8 * OutputChannelCount) ChannelMapping; + } + + aligned(8) class OpusDecoderConfigurationRecord { + unsigned int(8) Version; + unsigned int(8) OutputChannelCount; + unsigned int(16) PreSkip; + unsigned int(32) InputSampleRate; + signed int(16) OutputGain; + unsigned int(8) ChannelMappingFamily; + if (ChannelMappingFamily != 0) { + ChannelMappingTable(OutputChannelCount); + } + } + + class OpusSpecificBox extends Box('dOps') { + OpusDecoderConfigurationRecord() OpusConfig; + } + + + 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. + + 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 [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 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 [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 [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 [3]. Note that the value 255 may be used for an alternative + to map channels by ISO Base Media native mapping. The details are described in 4.5.1. + + StreamCount: + The StreamCount field shall be set to the same value as the *Stream Count* field in the identification + 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 [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 [3]. + + 4.3.3 Sample format + 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 [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]. + + +-----------------------------------------+-------------------------------------+ + | Opus packet 0 (self-delimiting framing) | Opus packet 1 (undelimited framing) | + +-----------------------------------------+-------------------------------------+ + |<---------------------------- the size of Opus sample ------------------------>| + + Figure 1 - Example structure of an Opus sample containing two Opus bitstreams + + 4.3.4 Duration of Opus sample + 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. + + 4.3.5 Sub-sample + 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. + + 4.3.6 Random Access + This subclause describes the nature of the random access of Opus sample. + + 4.3.6.1 Random Access Point + 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. And the sample_is_non_sync_sample field for Opus samples shall be set to 0. + + 4.3.6.2 Pre-roll + Opus bitstream requires at least 80 millisecond pre-roll after each random access to get correct output. + 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 any track containing Opus bitstreams, at least one Sample Group Description Box and at least one + Sample to Group Box within the Sample Table Box shall be present and these have the grouping_type field + set to 'roll'. If any Opus sample is contained in a track fragment, the Sample to Group Box with the + grouping_type field set to 'roll' shall be present for that track fragment. + + For the requirement of AudioRollRecoveryEntry, the compatible_brands field in the File Type Box shall + contain at least one brand which requires support for roll groups. + + 4.4 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, and the Edit Box and the Edit List Box shall be present. + + 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 timescale field in the Media Header Box is + typically set to 48000. It is recommended that the timescale field in the Movie Header Box be set to the same + value of the timescale field in the Media Header Box in order to avoid the rounding problem when specifying + duration of edit if the timescales in all of the Media Header Boxes are set to the same value. + + For example, to indicate the actual duration of an Opus bitstream in a track with the timescale fields of both + the Movie Header Box and the Media Header Box set to 48000, we would use the following edit: + segment_duration = the number of the valid samples + media_time = the number of the priming samples + media_rate = 1 << 16 + + 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 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. + + 4.5 Channel Mapping + 4.5.1 ISO Base Media native Channel Mapping + ISO Base Media File Format, that is ISO/IEC 14496-12 [1], defines an extension ChannelLayout to the + AudioSampleEntry, which conveys information of mapping channels to loudspeaker positions. The ChannelLayout + enables to specify the channel layout more flexibly than the predefined layouts of the ChannelMappingFamily. + + To utilize the ChannelLayout for OpusSampleEntry, the ChannelMappingFamily field should be set to 255. + Even when the ChannelMappingFamily field is set to another value, the assignment of each output channel to + loudspeaker position specified by the ChannelMappingFamily would be changed as specified by the ChannelLayout. + The procedure of the assignment is the following. + + 1. Decoded channels are mapped to output channels according to the ChannelMappingTable. + 2. Output channels are mapped to loudspeaker positions according to the ChannelLayout. + + In this way, the parameters of the Opus Specific Box are processed before the ChannelLayout, and the + ChannelLayout shall follow the Opus Specific Box. + + 4.5.2 Composition on all active tracks (informative) + 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, 4, 1, 2, 3, 5}; // front left, front center, front right, + // rear left, rear right, LFE + Here, to couple front left to front right channels into the first stream, and couple rear left to rear right + channels into the second stream, reordering is needed since coupled streams must precede any non-coupled + stream. 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. + + 4.6 Basic Structure (informative) + 4.6.1 Initial Movie + This subclause shows 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 Header 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 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. + For most boxes listed above, the definition is as is defined in ISO/IEC 14496-12 [1]. The additional boxes + and the additional requirements, restrictions and recommendations to the other boxes are described in this + specification. + + 4.6.2 Movie Fragments + This subclause shows 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 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. + Boxes marked with an asterisk (*) may be present. + For the boxes listed above, the definition is as is defined in ISO/IEC 14496-12 [1]. + + 4.7 Example of Encapsulation (informative) + [File] + size = 17757 + [ftyp: File Type Box] + position = 0 + size = 24 + major_brand = Opus : Opus audio coding + minor_version = 0 + compatible_brands + brand[0] = Opus : Opus audio coding + brand[1] = iso2 : ISO Base Media file format version 2 + [moov: Movie Box] + position = 24 + size = 757 + [mvhd: Movie Header Box] + position = 32 + size = 108 + version = 0 + flags = 0x000000 + creation_time = UTC 2014/12/12, 18:41:19 + modification_time = UTC 2014/12/12, 18:41:19 + 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 + [trak: Track Box] + position = 140 + size = 608 + [tkhd: Track Header Box] + position = 148 + size = 92 + version = 0 + flags = 0x000007 + Track enabled + Track in movie + Track in preview + creation_time = UTC 2014/12/12, 18:41:19 + modification_time = UTC 2014/12/12, 18:41:19 + 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 = 240 + size = 36 + [elst: Edit List Box] + position = 281 + size = 28 + version = 0 + flags = 0x000000 + entry_count = 1 + entry[0] + segment_duration = 33600 + media_time = 312 + media_rate = 1.000000 + [mdia: Media Box] + position = 276 + size = 472 + [mdhd: Media Header Box] + position = 284 + size = 32 + version = 0 + flags = 0x000000 + creation_time = UTC 2014/12/12, 18:41:19 + modification_time = UTC 2014/12/12, 18:41:19 + timescale = 48000 + duration = 34560 (00:00:00.720) + language = und + pre_defined = 0x0000 + [hdlr: Handler Reference Box] + position = 316 + 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 = 367 + size = 381 + [smhd: Sound Media Header Box] + position = 375 + size = 16 + version = 0 + flags = 0x000000 + balance = 0.000000 + reserved = 0x0000 + [dinf: Data Information Box] + position = 391 + size = 36 + [dref: Data Reference Box] + position = 399 + size = 28 + version = 0 + flags = 0x000000 + entry_count = 1 + [url : Data Entry Url Box] + position = 415 + size = 12 + version = 0 + flags = 0x000001 + location = in the same file + [stbl: Sample Table Box] + position = 427 + size = 321 + [stsd: Sample Description Box] + position = 435 + size = 79 + version = 0 + flags = 0x000000 + entry_count = 1 + [Opus: Audio Description] + position = 451 + size = 63 + reserved = 0x000000000000 + data_reference_index = 1 + reserved = 0x0000 + reserved = 0x0000 + reserved = 0x00000000 + channelcount = 6 + samplesize = 16 + pre_defined = 0 + reserved = 0 + samplerate = 48000.000000 + [dOps: Opus Specific Box] + position = 487 + size = 27 + Version = 0 + OutputChannelCount = 6 + PreSkip = 312 + InputSampleRate = 48000 + OutputGain = 0 + ChannelMappingFamily = 1 + StreamCount = 4 + CoupledCount = 2 + ChannelMapping + 0 -> 0: front left + 1 -> 4: fron center + 2 -> 1: front right + 3 -> 2: side left + 4 -> 3: side right + 5 -> 5: rear center + [stts: Decoding Time to Sample Box] + position = 514 + size = 24 + version = 0 + flags = 0x000000 + entry_count = 1 + entry[0] + sample_count = 18 + sample_delta = 1920 + [stsc: Sample To Chunk Box] + position = 538 + size = 40 + version = 0 + flags = 0x000000 + entry_count = 2 + entry[0] + first_chunk = 1 + samples_per_chunk = 13 + sample_description_index = 1 + entry[1] + first_chunk = 2 + samples_per_chunk = 5 + sample_description_index = 1 + [stsz: Sample Size Box] + position = 578 + size = 92 + version = 0 + flags = 0x000000 + sample_size = 0 (variable) + sample_count = 18 + entry_size[0] = 977 + entry_size[1] = 938 + entry_size[2] = 939 + entry_size[3] = 938 + entry_size[4] = 934 + entry_size[5] = 945 + entry_size[6] = 948 + entry_size[7] = 956 + entry_size[8] = 955 + entry_size[9] = 930 + entry_size[10] = 933 + entry_size[11] = 934 + entry_size[12] = 972 + entry_size[13] = 977 + entry_size[14] = 958 + entry_size[15] = 949 + entry_size[16] = 962 + entry_size[17] = 848 + [stco: Chunk Offset Box] + position = 670 + size = 24 + version = 0 + flags = 0x000000 + entry_count = 2 + chunk_offset[0] = 797 + chunk_offset[1] = 13096 + [sgpd: Sample Group Description Box] + position = 694 + size = 26 + version = 1 + flags = 0x000000 + grouping_type = roll + default_length = 2 (constant) + entry_count = 1 + roll_distance[0] = -2 + [sbgp: Sample to Group Box] + position = 720 + size = 28 + version = 0 + flags = 0x000000 + grouping_type = roll + entry_count = 1 + entry[0] + sample_count = 18 + group_description_index = 1 + [free: Free Space Box] + position = 748 + size = 8 + [mdat: Media Data Box] + position = 756 + size = 17001 + +5 Authors' Address + Yusuke Nakamura + Email: muken.the.vfrmaniac |at| gmail.com +