H265 Nalu type judgment and SPS data analysis

One ,Nalu analysis

First of all, let's introduce h265（HEVC）nal Unit head , And h264 Of nal Layer by layer ,h265 Of nal unit header It consists of two bytes , As shown in the figure below :

0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | F | Type | LayerId | TID | +------------ - +---------------- - +

Its syntax is defined in the following table ：

nal_unit_header( ) {	Descriptor
forbidden_zero_bit	f(1)
nal_unit_type	u(6)
nuh_reserved_zero_6bits	u(6)
nuh_temporal_id_plus1	u(3)
}

Nalu Type The definition of ：

enum NalUnitType { NAL_UNIT_CODED_SLICE_TRAIL_N = 0, // 0 NAL_UNIT_CODED_SLICE_TRAIL_R, // 1 NAL_UNIT_CODED_SLICE_TSA_N, // 2 NAL_UNIT_CODED_SLICE_TLA, // 3 NAL_UNIT_CODED_SLICE_STSA_N, // 4 NAL_UNIT_CODED_SLICE_STSA_R, // 5 NAL_UNIT_CODED_SLICE_RADL_N, // 6 NAL_UNIT_CODED_SLICE_DLP, // 7 NAL_UNIT_CODED_SLICE_RASL_N, // 8 NAL_UNIT_CODED_SLICE_TFD, // 9 NAL_UNIT_RESERVED_10, NAL_UNIT_RESERVED_11, NAL_UNIT_RESERVED_12, NAL_UNIT_RESERVED_13, NAL_UNIT_RESERVED_14, NAL_UNIT_RESERVED_15, NAL_UNIT_CODED_SLICE_BLA, // 16 NAL_UNIT_CODED_SLICE_BLA, // 16 NAL_UNIT_CODED_SLICE_BLANT, // 17 NAL_UNIT_CODED_SLICE_BLA_N_LP, // 18 NAL_UNIT_CODED_SLICE_IDR, // 19 // Current name in the spec: IDR_W_DLP NAL_UNIT_CODED_SLICE_IDR_N_LP, // 20 NAL_UNIT_CODED_SLICE_CRA, // 21 NAL_UNIT_RESERVED_22, NAL_UNIT_RESERVED_23, NAL_UNIT_RESERVED_24, NAL_UNIT_RESERVED_25, NAL_UNIT_RESERVED_26, NAL_UNIT_RESERVED_27, NAL_UNIT_RESERVED_28, NAL_UNIT_RESERVED_29, NAL_UNIT_RESERVED_30, NAL_UNIT_RESERVED_31, NAL_UNIT_VPS, // 32 NAL_UNIT_SPS, // 33 NAL_UNIT_PPS, // 34 NAL_UNIT_ACCESS_UNIT_DELIMITER, // 35 NAL_UNIT_EOS, // 36 NAL_UNIT_EOB, // 37 NAL_UNIT_FILLER_DATA, // 38 NAL_UNIT_SEI, // 39 Prefix SEI NAL_UNIT_SEI_SUFFIX, // 40 Suffix SEI NAL_UNIT_RESERVED_41, NAL_UNIT_RESERVED_42, NAL_UNIT_RESERVED_43, NAL_UNIT_RESERVED_44, NAL_UNIT_RESERVED_45, NAL_UNIT_RESERVED_46, NAL_UNIT_RESERVED_47, NAL_UNIT_UNSPECIFIED_48, NAL_UNIT_UNSPECIFIED_49, NAL_UNIT_UNSPECIFIED_50, NAL_UNIT_UNSPECIFIED_51, NAL_UNIT_UNSPECIFIED_52, NAL_UNIT_UNSPECIFIED_53, NAL_UNIT_UNSPECIFIED_54, NAL_UNIT_UNSPECIFIED_55, NAL_UNIT_UNSPECIFIED_56, NAL_UNIT_UNSPECIFIED_57, NAL_UNIT_UNSPECIFIED_58, NAL_UNIT_UNSPECIFIED_59, NAL_UNIT_UNSPECIFIED_60, NAL_UNIT_UNSPECIFIED_61, NAL_UNIT_UNSPECIFIED_62, NAL_UNIT_UNSPECIFIED_63, NAL_UNIT_INVALID, };

By recording H265 Of ES flow , Analyze NALU head , Found in 6 The beginning of each species is ：

1） 00 00 00 01 40 01

2） 00 00 00 01 42 01

3） 00 00 00 01 44 01

4） 00 00 00 01 4E 01

5） 00 00 00 01 26 01

6） 00 00 00 01 02 01

According to H265 Of NALU Type definition analysis ,

00 00 00 01 40 01 Of nuh_unit_type The value of is 32, The semantic is video parameter set

00 00 00 01 42 01 Of nuh_unit_type The value of is 33, Semantic sequence parameter set

00 00 00 01 44 01 Of nuh_unit_type The value of is 34, The semantic is the image parameter set

00 00 00 01 4E 01 Of nuh_unit_type The value of is 39, Semantics are supplementary and enhanced information

00 00 00 01 26 01 Of nuh_unit_type The value of is 19, Semantically, there may be RADL Graphic IDR Graphic SS Encoding data

00 00 00 01 02 01 Of nuh_unit_type The value of is 1, The semantic is the referenced post image , And not TSA、 Not STSA Of SS Encoding data

During coding , When getting the code stream from the encoder ,1、2、3、4、5 Is in a frame of data . amount to H264 Of I frame .

Two ,SPS analysis

a section HEVC The bitstream may contain one or more encoded video sequences CVS, Every CVS Start with a random access point , namely IDR/BLA/CRA. stay H.264 and HEVC in , Sequence parameter set SPS Include the CVS All in slice Information needed .SPS It can be divided into several parts ：

1、 bootstrap ID;

2、 Decode relevant information , Such as grade level 、 The resolution of the 、 The number of sublayers, etc ;

3、 Function switch identification and function parameters in a certain grade ;

4、 Restriction information on the flexibility of structure and transform coefficient coding ;

5、 Time domain scalable information ;

6、VUI.

The following is a discussion of each grammatical element ：

1、sps_video_parameter_set_id ： Specifies the currently active VPS Of ID Number , The value of the current example is 0, This is also the same as the VPS The result of analysis has been ;

2、sps_max_sub_layers_minus1 ： This value +1 Means to refer to the SPS Of CVS The maximum number of time domain sublayers included , Value range 0-6; The value in this example is 0, That is, only 1 Time domain sublayer ;

3、sps_temporal_id_nesting_flag ： The restriction information identifying the inter prediction reference frame in the time domain scalability ; Here, the value is taken as 0【 It seems to contradict the standard document ……】;

4、sps_seq_parameter_set_id ：【 In fact, before this parameter, there are still many data in the code stream that are not explained clearly , Save it for later 】 Ben SPS Of ID value , Take here 0;

5、chroma_format_idc： Chroma sampling format , The value here is 1, Representative adoption 4:2:0 Format ;

6、separate_colour_plane_flag ： This parameter is 4:4:4 Format specific , In this case... Does not exist ;

7、pic_width_in_luma_samples and pic_height_in_luma_samples ： Image resolution information , Code with exponential Columbus , This example takes 176*144;

8、conformance_window_flag ： Indicates the consistent window crop offset parameter conformance cropping window offset parameters Information about ; The value here is 1, Indicates that the following digits are conf_win_left_offset、conf_win_right_offset、conf_win_top_offset、conf_win_bottom_offset Equal parameter ;

9、bit_depth_luma_minus8 ： The bit depth of the luminance matrix and the luminance quantization parameter range offset are specified ; Take here 0, Each luminance pixel is represented by 8 To represent ,QpBdOffset Parameter is 0;

10、bit_depth_chroma_minus8 ： And bit_depth_luma_minus8 similar , It's just for chromaticity ;

11、log2_max_pic_order_cnt_lsb_minus4 ： Responsible for calculating variables MaxPicOrderCntLsb Value 【 What's this value for ……】;

12、sps_sub_layer_ordering_info_present_flag ： Time domain sublayer sequence identification switch , This value takes 1, It means that the following digits are sps_max_dec_pic_buffering、sps_num_reorder_pics、sps_max_latency_increase Equal parameter ;

13、log2_min_coding_block_size_minus3 ： Used to calculate the minimum brightness CB The size of the , Take here 0;

14、log2_diff_max_min_coding_block_size ： Used to calculate the maximum and minimum brightness CB Difference in size , Take here 3;

15、log2_min_transform_block_size_minus2： Used to calculate the minimum TB Size , Take here 0;

16、log2_diff_max_min_transform_block_size ： Used to calculate the maximum and minimum TB Difference in size , Take here 3;

17、max_transform_hierarchy_depth_inter ： Interframe mode CB in TB Maximum level depth of , Here is 2;

18、max_transform_hierarchy_depth_intra :： In frame mode CB in TB Maximum level depth of , Here is 2;

19、scaling_list_enabled_flag： Identifies whether a quantization list is used in transform coefficient quantization , Take here 0;

20、amp_enabled_flag ： Identify whether asymmetric motion division is used , Here is 1;

21、sample_adaptive_offset_enabled_flag ： Identify whether to use SAO, Here is 1;

22、pcm_enabled_flag ： Identify whether to use PCM, Here is 0, It's not practical PCM data ;

23、num_short_term_ref_pic_sets ： instructions SPS in short_term_ref_pic_set( ) The number of this structure , Here is 1;

24、long_term_ref_pics_present_flag ： Indicates whether a long-term reference frame is used in inter prediction , Here is 1, That is, the long-term reference frame ;

25、sps_temporal_mvp_enable_flag ： identification CVS Central African IDR Whether the header of the frame contains slice_temporal_mvp_enabled_flag identification , Here is 1, It contains ;

26、sps_strong_intra_smoothing_enable_flag ： Identify whether the bilinear difference method is used in the smoothing filtering process , Here is 1, That is to use ;

27、vui_parameters_present_flag ： Whether the sign has

The following is the parsing code

1、 Redefine the type

typedef unsigned char uint8; typedef unsigned short uint16; typedef unsigned longuint32; typedef unsigned __int64uint64; typedef signed charint8; typedef signed shortint16; typedef signed longint32; typedef signed __int64int64;

2、 Definition Sps Relevant parameters required

struct vc_params_t

{

    LONG width,height;

    DWORD profile, level;

    DWORD nal_length_size;

    void clear()

    {

   	memset(this, 0, sizeof(*this));

    }

};

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3、 Define the network abstraction layer Nal class

class NALBitstream

{

public:

NALBitstream() : m_data(NULL), m_len(0), m_idx(0), m_bits(0), m_byte(0), m_zeros(0) 

{

};


NALBitstream(void * data, int len) 

{

    Init(data, len); 

};

	
void Init(void * data, int len) 

{

    m_data = (LPBYTE)data;

    m_len = len;

m_idx = 0; 

    m_bits = 0;

    m_byte = 0; 

    m_zeros = 0; 

};


BYTE GetBYTE()

{

    if ( m_idx >= m_len )

	return 0;

    BYTE b = m_data[m_idx++];

    if ( b == 0 )

    {

   	m_zeros++;

   	if ( (m_idx < m_len) && (m_zeros == 2) && (m_data[m_idx] == 0x03) )

	{

		m_idx++;

		m_zeros=0;

	}

    } 

    else  m_zeros = 0;


return b;

};

	
	
UINT32 GetBit() 

{

    if (m_bits == 0) 

    {

	m_byte = GetBYTE();

	m_bits = 8;

    }

    
    m_bits--;

    return (m_byte >> m_bits) & 0x1;

};

	
	
UINT32 GetWord(int bits) 

{

    UINT32 u = 0;

    while ( bits > 0 )

    {

   	u <<= 1;

   	u |= GetBit();

   	bits--;

    }

    return u;

};

	
UINT32 GetUE() 

{

    int zeros = 0;

    while (m_idx < m_len && GetBit() == 0 ) 
        zeros++;

    return GetWord(zeros) + ((1 << zeros) - 1);

};

	
	
INT32 GetSE()

{

    UINT32 UE = GetUE();

    bool positive = UE & 1;

    INT32 SE = (UE + 1) >> 1;

    if ( !positive )

	SE = -SE;



    return SE;

};

private:

    LPBYTE m_data;

    int m_len;
    int m_idx;

    int m_bits;

    BYTE m_byte;

    int m_zeros;

};


bool  ParseSequenceParameterSet(BYTE* data,int size, vc_params_t& params)

{

    if (size < 20)

   	return false;

  

    NALBitstream bs(data, size);

    // seq_parameter_set_rbsp()

    bs.GetWord(4);// sps_video_parameter_set_id

    int sps_max_sub_layers_minus1 = bs.GetWord(3); 

    if (sps_max_sub_layers_minus1 > 6) 

   	return false;

    
    bs.GetWord(1); 

    bs.GetWord(2); 

    bs.GetWord(1); 

    params.profile = bs.GetWord(5); 

    bs.GetWord(32);//

    bs.GetWord(1);// 

    bs.GetWord(1);// 

    bs.GetWord(1);// 

    bs.GetWord(1);//  

    bs.GetWord(44);// 

    params.level   = bs.GetWord(8);// general_level_idc

    uint8 sub_layer_profile_present_flag[6] = {0};

    uint8 sub_layer_level_present_flag[6]   = {0};


    for (int i = 0; i < sps_max_sub_layers_minus1; i++)
    {

        sub_layer_profile_present_flag[i]= bs.GetWord(1);

	sub_layer_level_present_flag[i]= bs.GetWord(1);

    }


    if (sps_max_sub_layers_minus1 > 0) 

    {

        for (int i = sps_max_sub_layers_minus1; i < 8; i++) 

	uint8 reserved_zero_2bits = bs.GetWord(2);

	 

    }

		
    for (int i = 0; i < sps_max_sub_layers_minus1; i++) 

    {

        if (sub_layer_profile_present_flag[i])
        {

	bs.GetWord(2); 

	bs.GetWord(1); 

	bs.GetWord(5);/ 

	bs.GetWord(32); 

	bs.GetWord(1); 

	bs.GetWord(1); 

	bs.GetWord(1); 

	bs.GetWord(1); 

	bs.GetWord(44); 

	}

	
	if (sub_layer_level_present_flag[i]) 

	bs.GetWord(8);// sub_layer_level_idc[i]    

    }

	
    uint32 sps_seq_parameter_set_id= bs.GetUE();  

    if (sps_seq_parameter_set_id > 15) 

   	return false;

    

    uint32 chroma_format_idc = bs.GetUE();  

    if (sps_seq_parameter_set_id > 3)  

   	return false;

 

    if (chroma_format_idc == 3)  

   	bs.GetWord(1);//  

 

    params.width  = bs.GetUE(); // pic_width_in_luma_samples

    params.height  = bs.GetUE(); // pic_height_in_luma_samples

    if (bs.GetWord(1)) 
    { 

	bs.GetUE();  

	bs.GetUE();  

	bs.GetUE();  

	bs.GetUE();  

    }


    uint32 bit_depth_luma_minus8= bs.GetUE();

    uint32 bit_depth_chroma_minus8= bs.GetUE();

    if (bit_depth_luma_minus8 != bit_depth_chroma_minus8) 

   	return false;

 

//...

}

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4、 Test code