X264学习笔记（1）
X264编码流程
参数的初始化
1.opt，param根据输入的参数和标准的规定，进行初始化设置。
Opt的说明如下：
Opt->hin用于给出读入的yuv文件的指针地址
Opt->hout给出了输出的文件的指针地址
Opt->i_seek给出了起始编码帧的帧数，是由编码时的seek命令参数决定的
如：
X264 -seek 10 -o foreman.cif test.264 352x288
i_seek 设为10，表示起始编码的帧为元序列的第十帧
Opt->qpfile按照说明，为qp值文件输入进行定义这种方式的接口，可以通过读入标准的文件格式，对编码时的qp值进行定义。
Param的说明：
typedef struct
{
/* CPU flags */
unsigned int cpu;
int i_threads; /* divide each frame into multiple slices, encode in parallel */线程数，用于多线程并行编码
/* Video Properties */
int i_width; 图像的宽度
int i_height; 图像的高度
int i_csp; /* CSP of encoded bitstream, only i420 supported */ 色彩空间的设置
int i_level_idc; level 值的设置
int i_frame_total; /* number of frames to encode if known, else 0 */ 总共需要编码的帧数，由--frames设置
Vui参数集
struct
{
/* they will be reduced to be 0 < x <= 65535 and prime */
int i_sar_height;
int i_sar_width;
int i_overscan; /* 0=undef, 1=no overscan, 2=overscan */
/* see h264 annex E for the values of the following */
int i_vidformat;
int b_fullrange;
int i_colorprim;
int i_transfer;
int i_colmatrix;
int i_chroma_loc; /* both top & bottom */
} vui;
int i_fps_num;
int i_fps_den;
这两个参数是由fps帧率确定的，赋值的过程见下：
{
float fps;
if( sscanf( value, "%d/%d", &p->i_fps_num, &p->i_fps_den ) == 2 )
;
else if( sscanf( value, "%f", &fps ) )
{
p->i_fps_num = (int)(fps * 1000 + .5);
p->i_fps_den = 1000;
}
else
b_error = 1;
}
Value的值就是fps。
/* Bitstream parameters */
int i_frame_reference; /* Maximum number of reference frames */
int i_keyint_max; /* Force an IDR keyframe at this interval */
int i_keyint_min; /* Scenecuts closer together than this are coded as I, not IDR. */
int i_scenecut_threshold; /* how aggressively to insert extra I frames */
int i_bframe; /* how many b-frame between 2 references pictures */
int b_bframe_adaptive;
int i_bframe_bias;
int b_bframe_pyramid; /* Keep some B-frames as references */
去块滤波器需要的参数
int b_deblocking_filter;
int i_deblocking_filter_alphac0; /* [-6, 6] -6 light filter, 6 strong */
int i_deblocking_filter_beta; /* [-6, 6] idem */
熵编码
int b_cabac;
int i_cabac_init_idc;
量化
int i_cqm_preset;
char *psz_cqm_file; /* JM format */
uint8_t cqm_4iy[16]; /* used only if i_cqm_preset == X264_CQM_CUSTOM */
uint8_t cqm_4ic[16];
uint8_t cqm_4py[16];
uint8_t cqm_4pc[16];
uint8_t cqm_8iy[64];
uint8_t cqm_8py[64];
/* Log */
void (*pf_log)( void *, int i_level, const char *psz, va_list );
void *p_log_private;
int i_log_level;
int b_visualize;
/* Encoder analyser parameters */
struct
{
unsigned int intra; /* intra partitions */
unsigned int inter; /* inter partitions */
int b_transform_8x8;
int b_weighted_bipred; /* implicit weighting for B-frames */
int i_direct_mv_pred; /* spatial vs temporal mv prediction */
int i_chroma_qp_offset;
int i_me_method; /* motion estimation algorithm to use (X264_ME_*) */
int i_me_range; /* integer pixel motion estimation search range (from predicted mv) */
int i_mv_range; /* maximum length of a mv (in pixels) */
int i_subpel_refine; /* subpixel motion estimation quality */
int b_bidir_me; /* jointly optimize both MVs in B-frames */
int b_chroma_me; /* chroma ME for subpel and mode decision in P-frames */
int b_bframe_rdo; /* RD based mode decision for B-frames */
int b_mixed_references; /* allow each mb partition in P-frames to have it's own reference number */
int i_trellis; /* trellis RD quantization */
int b_fast_pskip; /* early SKIP detection on P-frames */
int b_dct_decimate; /* transform coefficient thresholding on P-frames */
int i_noise_reduction; /* adaptive pseudo-deadzone */
int b_psnr; /* Do we compute PSNR stats (save a few % of cpu) */
} analyse;
/* Rate control parameters */
struct
{
int i_rc_method; /* X264_RC_* */
int i_qp_constant; /* 0-51 */
int i_qp_min; /* min allowed QP value */
int i_qp_max; /* max allowed QP value */
int i_qp_step; /* max QP step between frames */
int i_bitrate; 比特率 --bitrate控制
int i_rf_constant; /* 1pass VBR, nominal QP */
float f_rate_tolerance;
int i_vbv_max_bitrate;
int i_vbv_buffer_size;
float f_vbv_buffer_init;
float f_ip_factor;
float f_pb_factor;
/* 2pass */
int b_stat_write; /* Enable stat writing in psz_stat_out */
char *psz_stat_out;
int b_stat_read; /* Read stat from psz_stat_in and use it */
char *psz_stat_in;
/* 2pass params (same as ffmpeg ones) */
char *psz_rc_eq; /* 2 pass rate control equation */
float f_qcompress; /* 0.0 => cbr, 1.0 => constant qp */
float f_qblur; /* temporally blur quants */
float f_complexity_blur; /* temporally blur complexity */
x264_zone_t *zones; /* ratecontrol overrides */
int i_zones; /* sumber of zone_t's */
char *psz_zones; /* alternate method of specifying zones */
} rc;
/* Muxing parameters */
int b_aud; /* generate access unit delimiters */
int b_repeat_headers; /* put SPS/PPS before each keyframe */
int i_sps_id; /* SPS and PPS id number */
} x264_param_t;