X264學習筆記（1）

X264編碼流程

參數的初始化

1.opt，param根據輸入的參數和標準的規定，進行初始化設置。

Opt的說明如下：

Opt->hin用于給出讀入的yuv文件的指針地址

Opt->hout給出了輸出的文件的指針地址

Opt->i_seek給出了起始編碼幀的幀數，是由編碼時的seek命令參數決定的

如：

X264 -seek 10 -o foreman.cif test.264 352x288

i_seek 設為10，表示起始編碼的幀為元序列的第十幀

Opt->qpfile按照說明，為qp值文件輸入進行定義這種方式的接口，可以通過讀入標準的文件格式，對編碼時的qp值進行定義。

Param的說明：

typedef struct

{

??? /* CPU flags */

??? unsigned int cpu;

??? int???????? i_threads;? /* divide each frame into multiple slices, encode in parallel */線程數，用于多線程并行編碼

?

??? /* Video Properties */

??? int???????? i_width; ????????????????????????????? 圖像的寬度

??? int???????? i_height;?????????????????????????????? 圖像的高度

??? int???????? i_csp;? /* CSP of encoded bitstream, only i420 supported */ ?? 色彩空間的設置

??? int???????? i_level_idc; ????????????level 值的設置

??? int???????? i_frame_total; /* number of frames to encode if known, else 0 */? 總共需要編碼的幀數，由--frames設置

Vui參數集

??? struct

??? {

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

??????? int???????? i_sar_height;

??????? int???????? i_sar_width;

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??????? 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;

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??? int???????? i_fps_num;

??? int???????? i_fps_den;

這兩個參數是由fps幀率確定的，賦值的過程見下：

??? {

??????? 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。

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??? /* 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 */

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去塊濾波器需要的參數

??? int???????? b_deblocking_filter;

??? int???????? i_deblocking_filter_alphac0;??? /* [-6, 6] -6 light filter, 6 strong */

??? int???????? i_deblocking_filter_beta;?????? /* [-6, 6]? idem */

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熵編碼

??? 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 */

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??????? 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;

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??????? 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 */

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??????? int????????? b_psnr;??? /* Do we compute PSNR stats (save a few % of cpu) */

??? } analyse;

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??? /* Rate control parameters */

??? struct

??? {

??????? int???????? i_rc_method;??? /* X264_RC_* */

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??????? 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 */

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??????? 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;

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??? /* 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;

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