parse AVCDecoderConfigurationRecord example

AVCDecoderConfigurationRecord.md

以下は、AVCDecoderConfigurationRecord のバイトデータです。

ADDR    0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
------ -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
000000 00 00 00 2e 61 76 63 43 01 42 c0 1e ff e1 00 16
000010 67 42 c0 1e d9 02 04 68 40 00 00 03 01 40 00 00
000020 03 00 83 c5 8b 92 01 00 05 68 cb 83 cb 20

このバイト列は以下のようにデコードされます

bytes	filed	値,説明
00 00 00 2e	BoxSize	'avcC' の Box サイズ
61 76 63 43	BoxType	'avcC'
01	configurationVersion	通常は1です
42	AVCProfileIndication	0x42(66), AVCのプロファィル(profile_idc)です 66はBaseline profileです
c0	profile_compatibility	SPS の互換性情報です
1e	AVCLevelIndication	30, Level です。30 は 3.0 になります
ff	lengthSizeMinusOne	111111 + 11, NALUnit の長さ部分のバイト数は通常4ですが、 1,2,4 byte にも変更できます。3は不正な値です。 実際のbyte数から1引いた値になります
e1	numOfSequenceParameterSets	111 + 00001, SPS のパラメタセット数です
00 16	sequenceParameterSetLength	0x0016(22). SPS NALU のバイト数です
67 42 .. 8b 92	sequenceParameterSetNALUnit	22byte の SPS NALU です
01	numOfPictureParameterSets	0x01. PPS NALU のパラメタセット数です
00 05	pictureParameterSetLength	0x05. PPS NALU のバイト数です
68 cb 83 cb 20	pictureParameterSetNALUnit	5byte の PPS NALU です

バイト列にマッピングし直すとこのようになります。

ADDR    0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
------ -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
000000 00 00 00 2e 61 76 63 43 01 42 c0 1e ff e1 00 16
       ~~~~~~~~~~~                                      -> BoxSize
                   ~~~~~~~~~~~                          -> BoxType
                               ~~                       -> configurationVersion
                                  ~~                    -> AVCProfileIndication
                                     ~~                 -> profile_compatibility
                                        ~~              -> AVCLevelIndication
                                           ~~           -> lengthSizeMinusOne
                                              ~~        -> numOfSequenceParameterSets
                                                 ~~~~~  -> sequenceParameterSetLength
000010 67 42 c0 1e d9 02 04 68 40 00 00 03 01 40 00 00
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  -> sequenceParameterSetNALUnit
000020 03 00 83 c5 8b 92 01 00 05 68 cb 83 cb 20
       ~~~~~~~~~~~~~~~~~                                -> sequenceParameterSetNALUnit
                         ~~                             -> numOfPictureParameterSets
                            ~~~~~                       -> pictureParameterSetLength
                                  ~~~~~~~~~~~~~~        -> pictureParameterSetNALUnit

規格書(ISO/IEC 14496-15) の該当部分からの引用です。

5.2.4.1.1 Syntax

aligned(8) class AVCDecoderConfigurationRecord {
    unsigned int(8) configurationVersion = 1;
    unsigned int(8) AVCProfileIndication;
    unsigned int(8) profile_compatibility;
    unsigned int(8) AVCLevelIndication;
    bit(6) reserved = ‘111111’b;
    unsigned int(2) lengthSizeMinusOne;
    bit(3) reserved = ‘111’b;
    unsigned int(5) numOfSequenceParameterSets;
    for (i=0; i< numOfSequenceParameterSets; i++) {
      unsigned int(16) sequenceParameterSetLength ;
      bit(8*sequenceParameterSetLength) sequenceParameterSetNALUnit;
    }
    unsigned int(8) numOfPictureParameterSets;
    for (i=0; i< numOfPictureParameterSets; i++) {
      unsigned int(16) pictureParameterSetLength;
      bit(8*pictureParameterSetLength) pictureParameterSetNALUnit;
    }
}

• AVCProfileIndication contains the profile code as defined in ISO/IEC 14496-10. profile_compatibility is a byte defined exactly the same as the byte which occurs between the
• profile_IDC and level_IDC in a sequence parameter set (SPS), as defined in ISO/IEC 14496-10.
• AVCLevelIndication contains the level code as defined in ISO/IEC 14496-10.
• lengthSizeMinusOne indicates the length in bytes of the NALUnitLength field in an AVC video sample or AVC parameter set sample of the associated stream minus one. For example, a size of one byte is indicated with a value of 0. The value of this field shall be one of 0, 1, or 3 corresponding to a length encoded with 1, 2, or 4 bytes, respectively.
• numOfSequenceParameterSets indicates the number of SPSs that are used as the initial set of SPSs for decoding the AVC elementary stream.
• sequenceParameterSetLength indicates the length in bytes of the SPS NAL unit as defined in ISO/IEC 14496-10.
• sequenceParameterSetNALUnit contains a SPS NAL unit, as specified in ISO/IEC 14496-10. SPSs shall occur in order of ascending parameter set identifier with gaps being allowed.
• numOfPictureParameterSets indicates the number of picture parameter sets (PPSs) that are used as the initial set of PPSs for decoding the AVC elementary stream.
• pictureParameterSetLength indicates the length in bytes of the PPS NAL unit as defined in ISO/IEC 14496-10.
• pictureParameterSetNALUnit contains a PPS NAL unit, as specified in ISO/IEC 14496-10. PPSs shall occur in order of ascending parameter set identifier with gaps being allowed.