x264 struct学习 1

x264_t 结构体维护着CODEC的诸多重要信息

其中成员frames是一个指示和控制帧编码过程的结构。其中current是已经准备就绪可以编码的帧，其类型已经确定；next是尚未确定类型的帧；unused用于回收不使用的frame结构体以备今后再次使用。

struct x264_t ////

{

/* cpu capabilities */

unsigned int cpu;

/* bitstream output */

struct

{

int i_nal; //定义一个网络提取层//

x264_nal_t nal[3]; /* for now 3 is enought */

int i_bitstream; /* size of p_bitstream */

uint8_t *p_bitstream; /* will hold data for all nal */

bs_t bs;

} out;

/* encoder parameters */

x264_param_t param;

/* frame number/poc (TODO: rework that for B-frame) */

int i_frame; //一个指示和控制帧编码过程的结构

int i_poc;

int i_frame_offset; /* decoding only */

int i_frame_num; /* decoding only*/

int i_poc_msb; /* decoding only */

int i_poc_lsb; /* decoding only */

/* We use only one SPS and one PPS */

x264_sps_t sps_array[32];

x264_sps_t *sps;

x264_pps_t pps_array[256];

x264_pps_t *pps;

int i_idr_pic_id;

/* Slice header */

x264_slice_header_t sh;
/*cabac context */

x264_cabac_t cabac;

/*current picture being encoded */

x264_picture_t *picture;

/*bframe handling (only encoding for now) */

x264_frame_t *bframe_current[X264_BFRAME_MAX]; /* store the sequence of b frame being encoded */

x264_frame_t *frame_next[X264_BFRAME_MAX+1]; /* store the next sequence of frames to be encoded */这个是定义下一个帧,但不一定是B帧

x264_frame_t *frame_unused[X264_BFRAME_MAX+1]; /* store unused frames */

/*frame being reconstructed */

x264_frame_t *fdec;

/*Current MB DCT coeffs */

struct

{

DECLARE_ALIGNED( int, luma16×16_dc[16], 16 );

DECLARE_ALIGNED( int, chroma_dc[2][4], 16 );//色度

struct

{

DECLARE_ALIGNED( int, residual_ac[15], 16 );

DECLARE_ALIGNED( int, luma4×4[16], 16 );

} block[16+8];16*8的宏快的取用情况

} dct;离散余弦变换

/* MBtable and cache for current frame/mb */

struct

{

/*Strides */

int i_mb_stride;

/*Current index */

int i_mb_x;

int i_mb_y;

int i_mb_xy;

unsigned int i_neighbour;

/* mb table */

int8_t *type; /*mb type */

int8_t *qp; /* mb qp */

int16_t *cbp; ？ /* mbcbp: 0×0?: luma, 0x?0: chroma, 0×100: luma dc, 0×0200 and 0×0400: chroma
dc (all set for PCM)*/

int8_t (*intra4×4_pred_mode)[7]; /* intra4×4 predmode. for non I4×4 set to I_PRED_4×4_DC(2) */

uint8_t (*non_zero_count)[16+4+4]; /* nzc. for I_PCMset to 16 */

int8_t *chroma_pred_mode; /*chroma_pred_mode. cabac only. for non intra I_PRED_CHROMA_DC(0) */

int16_t (*mv[2])[2]; /* mb mv. set to 0 for intra mb */

int16_t (*mvd[2])[2]; /* mb mv difference with predict. set to 0 if intra. cabac only */

int8_t *ref[2]; /*mb ref. set to -1 if non used (intra or Lx only */

/*current value */

int i_type;

int i_partition;

int i_sub_partition[4];

int i_cbp_luma;

int i_cbp_chroma;

int i_intra16×16_pred_mode;

int i_chroma_pred_mode;

struct

{

/*pointer over mb of the frame to be compressed */

uint8_t *p_img[3];

int i_img[3];

/*pointers over mb of references and reconstrucated frame */

uint8_t *p_fdec[3];

uint8_t*p_fref[2][16][3];

int i_fdec[3]; /* same strides for p_fdec/p_fref */

} pic;

/*cache */

struct

{

/*real intra4×4_pred_mode if I_4X4, I_PRED_4×4_DC if mb available, -1 if not */

int intra4×4_pred_mode[X264_SCAN8_SIZE];色度预测模式

/*i_non_zero_count if availble else 0×80 */

int non_zero_count[X264_SCAN8_SIZE];

/*-1 if unused, -2 if unavaible */

int8_t ref[2][X264_SCAN8_SIZE];

/*0 if non avaible */

int16_t mv[2][X264_SCAN8_SIZE][2];

int16_t mvd[2][X264_SCAN8_SIZE][2];运动矢量与真实值之间的差

} cache;

/**/

int i_last_qp; /* last qp */

int i_last_dqp; /*last delta qp */

} mb;宏快的预测以及运动补偿和运动估计

/*frames used for reference */

x264_frame_t *freference[16+1]; /* all references frames plus current */

int i_ref0; 参考帧列表一（定义为lsit0意为向前预测编码）

x264_frame_t *fref0[16]; /* ref list 0*/

int i_ref1;参考帧列表二（定义为lsit1意为向后预测编码）

x264_frame_t *fref1[16]; /* ref list 1*/

/*rate control encoding only */

x264_ratecontrol_t *rc;

/*stats */

struct

{

/*per slice info */

int i_slice_count[5];

int i_slice_size[5];

float f_psnr_y[5];

float f_psnr_u[5];

float f_psnr_v[5];

int i_mb_count[5][18];

} stat;声明每一片的参数变量

/* CPU functions dependants */

x264_predict_t predict_16×16[4+3];

x264_predict_t predict_8×8[4+3];

x264_predict_t predict_4×4[9+3];

x264_pixel_function_t pixf;

x264_mc_function_t mc[2];

x264_dct_function_t dctf;

/* vlc table for decoding purpose only */

x264_vlc_table_t *x264_coeff_token_lookup[5];

x264_vlc_table_t *x264_level_prefix_lookup;

x264_vlc_table_t *x264_total_zeros_lookup[15];

x264_vlc_table_t *x264_total_zeros_dc_lookup[3];

x264_vlc_table_t *x264_run_before_lookup[7];

};

#endif

给出编码过程中的各个参数的初始化

x264_param_t

typedef struct

{

/* CPU flags */

unsigned int cpu;

/* Video Properties */

int i_width;

int i_height;

struct

{

/*they will be reduced to be 0 < x <= 65535 and prime */

int i_sar_height;

int i_sar_width;

} vui;？

float f_fps;
/* Used for rate control only */

/*Bitstream parameters */

int i_frame_reference; /* Maximum number of reference frames */

int i_idrframe; /*every i_idrframe I frame are marked as IDR */

int i_iframe; /* every i_iframe are intra */

int i_bframe; /* how many b-frame between 2 references pictures */

int b_deblocking_filter;

int b_cabac;

int i_cabac_init_idc;给出熵编码初始化时表格的选择

int i_qp_constant; /* 1-51 */

int i_bitrate; /* not working yet */

/* Encoder analyser parameters */

struct

{

unsigned int intra; /* intra flags */

unsigned int inter; /* inter flags */

} analyse;

}
x264_param_t给出编码过程中的各个参数的初始化

sps序列参数集

typedef struct

{

int i_id;

int i_profile_idc;指明所用profile

int i_level_idc; 指明所用level

int b_constraint_set0;

int b_constraint_set1;

int b_constraint_set2; 当他们值等于1时，表示必须遵守某些制约条件

int i_log2_max_frame_num;表示图像解码顺序的最大取值

int i_poc_type; /* poc 0 */

int i_log2_max_poc_lsb; /* poc 1 */

int b_delta_pic_order_always_zero;其值等于一时句法元素delta_pic_order_cnt[0]和 delta_pic_order_cnt[1]不再片头出现，且他们的默认值都为0。为0时上述则出现。

int i_offset_for_non_ref_pic;用来计算非参考帧或场的picture order count ,其值应在[-2e31,2e31-1]

int i_offset_for_top_to_bottom_field; 用来计算帧的底场的picture order count 其值应在[-2e31,2e31-1]

int i_num_ref_frames_in_poc_cycle;用来解码picture order count 取值应在[0，255]之间

int i_offset_for_ref_frame[256]; 当picture order count type=1时用来解码poc，这句语法对循环num_ref_frames_in_poc_cycle中的每一个元素指定了一个偏移

int i_num_ref_frames;指定参考帧队列的最大长度 h264规定最多可为16个参考帧

int b_gaps_in_frame_num_value_allowed;值为1时表示允许句法frame_num可以不连续

int i_mb_width;

int i_mb_height;

int b_frame_mbs_only;

int b_mb_adaptive_frame_field;

int b_direct8×8_inference;指明b片的直接和skip模式下运动矢量的预测方法

int b_crop;

struct

{

int i_left;

int i_right;

int i_top;

int i_bottom;

} crop;图像剪彩后输出的参数

int b_vui;

struct

{

int i_sar_width;

int i_sar_height;

/* FIXME to complete */

} vui;

}
x264_sps_t定义序列参考队列的参数以及初始化

pps图像参数集

typedef struct

{

int i_id;

int i_sps_id;

int b_cabac;

int b_pic_order;

int i_num_slice_groups; 加一表示图像中片组的个数

int i_slice_group_map_type;片组分割类型 /*i_slice_group_map_type == 0 */

int i_run_length[256]; 指明片组类型为2时每个片组连续的map_units的个数 /* FIXME */

/*i_slice_group_map_type == 2 */

int i_top_left[256]; /* FIXME */

int i_bottom_right[256]; /* FIXME */

/*i_slice_group_map_type == 3, 4, 5 */

int b_slice_group_change_direction; 当类型为345时与下句语法一起指明片组分割方法

int i_slice_group_change_rate; /*i_slice_group_map_type == 6 */

int i_pic_size_in_map_units;类型为6时指明图像以map_units为单位的大小

int i_slice_group_id[256]; /* FIXME */指明map_units属于哪个片组

int i_num_ref_idx_l0_active;加1为参考帧队列的长度 此为list0

int i_num_ref_idx_l1_active;此为list1

int b_weighted_pred;用以指明是否允许P和SP片的加权预测

int b_weighted_bipred; 用以指明是否允许B片的加权预测

int i_pic_init_qp;加26后用以指明亮度分量的量化参数的初始值

int i_pic_init_qs;同上只是用于SP和SI

int i_chroma_qp_index_offset;指明计算使用时用到的参数

int b_deblocking_filter_control;

int b_constrained_intra_pred;控制PB帧的帧内编码

int b_redundant_pic_cnt;是否出现redundant_pic_cnt句法元素

} x264_pps_t