x264 main函數走讀

可以看到，x264的main函數較為簡單，主要由x264_param_default、parse、encode和x264_param_cleanup三個函數。首先x264_param_default函數對參數進行預設設定，通過parse解析指令行，然後調用encode進行編碼，編碼結束後，調用x264_param_cleanup對參數進行cleanup。

代碼走讀：

REALIGN_STACK int main( int argc, char **argv )
{
    if( argc == 4 && !strcmp( argv[1], "--autocomplete" ) )
        return x264_cli_autocomplete( argv[2], argv[3] );
    
    // 參數集
    x264_param_t param;
    cli_opt_t opt = {0};
    int ret = 0;

    FAIL_IF_ERROR( x264_threading_init(), "unable to initialize threading\n" );

#ifdef _WIN32
    FAIL_IF_ERROR( !get_argv_utf8( &argc, &argv ), "unable to convert command line to UTF-8\n" );

    GetConsoleTitleW( org_console_title, CONSOLE_TITLE_SIZE );
    _setmode( _fileno( stdin ),  _O_BINARY );
    _setmode( _fileno( stdout ), _O_BINARY );
    _setmode( _fileno( stderr ), _O_BINARY );
#endif

    // 設定預設參數值
    x264_param_default( &param );
    /* Parse command line */
    if( parse( argc, argv, &param, &opt ) < 0 )
        ret = -1;

#ifdef _WIN32
    /* Restore title; it can be changed by input modules */
    SetConsoleTitleW( org_console_title );
#endif

    /* Control-C handler */
    signal( SIGINT, sigint_handler );

    if( !ret )
        ret = encode( &param, &opt );  // 編碼

    /* clean up handles */
    if( filter.free )
        filter.free( opt.hin );
    else if( opt.hin )
        cli_input.close_file( opt.hin );
    if( opt.hout )
        cli_output.close_file( opt.hout, 0, 0 );
    if( opt.tcfile_out )
        fclose( opt.tcfile_out );
    if( opt.qpfile )
        fclose( opt.qpfile );
    x264_param_cleanup( &param );

#ifdef _WIN32
    SetConsoleTitleW( org_console_title );
    free( argv );
#endif

    return ret;
}
           

x264_param_default函數走讀：

REALIGN_STACK void x264_param_default( x264_param_t *param )
{
    /* param參數初始為0*/
    memset( param, 0, sizeof( x264_param_t ) );

    /* CPU autodetect */
    param->cpu = x264_cpu_detect();  // 檢查目前機器的cpu信号，x264使用不同平台，對不同平台做了不同優化
    param->i_threads = X264_THREADS_AUTO;  // encode multiple frames in parallel, 預設為0
    param->i_lookahead_threads = X264_THREADS_AUTO; // multiple threads for lookahead analysis,線程超前緩存幀數
    param->b_deterministic = 1;  // 多線程的時候允許非确定性優化
    param->i_sync_lookahead = X264_SYNC_LOOKAHEAD_AUTO;  // Automatically select optimal lookahead thread buffer size

    /* Video properties */
    param->i_csp           = X264_CHROMA_FORMAT ? X264_CHROMA_FORMAT : X264_CSP_I420;
    param->i_width         = 0;
    param->i_height        = 0;
    param->vui.i_sar_width = 0;
    param->vui.i_sar_height= 0;
    param->vui.i_overscan  = 0;  /* undef */
    param->vui.i_vidformat = 5;  /* undef */
    param->vui.b_fullrange = -1; /* default depends on input */
    param->vui.i_colorprim = 2;  /* undef */
    param->vui.i_transfer  = 2;  /* undef */
    param->vui.i_colmatrix = -1; /* default depends on input */
    param->vui.i_chroma_loc= 0;  /* left center */
    param->i_fps_num       = 25;
    param->i_fps_den       = 1;
    param->i_level_idc     = -1;
    param->i_slice_max_size = 0;
    param->i_slice_max_mbs = 0;
    param->i_slice_count = 0;
#if HAVE_BITDEPTH8
    param->i_bitdepth = 8;
#elif HAVE_BITDEPTH10
    param->i_bitdepth = 10;
#else
    param->i_bitdepth = 8;
#endif

    /* Encoder parameters */
    param->i_frame_reference = 3;
    param->i_keyint_max = 250;
    param->i_keyint_min = X264_KEYINT_MIN_AUTO;
    param->i_bframe = 3;  // 兩個參考幀之間的B幀數目
    param->i_scenecut_threshold = 40;
    param->i_bframe_adaptive = X264_B_ADAPT_FAST; // 自适應B幀判定, 可選取值：X264_B_ADAPT_FAST等
    param->i_bframe_bias = 0; // 控制B幀替代P幀的機率，範圍-100 ~ +100，該值越高越容易插入B幀，預設0.
    param->i_bframe_pyramid = X264_B_PYRAMID_NORMAL; // 允許部分B幀為參考幀，可選取值：0=off,  1=strict hierarchical,  2=normal
    param->b_interlaced = 0;
    param->b_constrained_intra = 0;

    param->b_deblocking_filter = 1; // 去塊濾波開關
    param->i_deblocking_filter_alphac0 = 0; //  [-6, 6] -6 light filter, 6 strong
    param->i_deblocking_filter_beta = 0;  //  [-6, 6] 同上

    param->b_cabac = 1;
    param->i_cabac_init_idc = 0;  //  給出算術編碼初始化時表格的選擇

    param->rc.i_rc_method = X264_RC_CRF;  // 碼率控制方式 ： X264_RC_CQP恒定品質,  
X264_RC_CRF恒定碼率,  X264_RC_ABR平均碼率
    param->rc.i_bitrate = 0;
    param->rc.f_rate_tolerance = 1.0;  // 允許的誤差
    param->rc.i_vbv_max_bitrate = 0;  // 平均碼率模式下，最大瞬時碼率，預設0
    param->rc.i_vbv_buffer_size = 0;  // 碼率控制緩沖區的大小，機關kbit，預設0
    param->rc.f_vbv_buffer_init = 0.9; // 設定碼率控制緩沖區（VBV）緩沖達到多滿(百分比)，才開始回放，
    param->rc.i_qp_constant = -1;  // 指定P幀的量化值，0 - 51，0表示無損
    param->rc.f_rf_constant = 23;  // 1pass VBR, nominal QP. 實際品質，值越大圖像越花,越小越清晰
    param->rc.i_qp_min = 0;
    param->rc.i_qp_max = INT_MAX;
    param->rc.i_qp_step = 4;  // 幀間最大量化步長
    param->rc.f_ip_factor = 1.4;  // I幀和P幀之間的量化因子（QP）比值，預設1.4
    param->rc.f_pb_factor = 1.3;  // P幀和B幀之間的量化因子（QP）比值，預設1.3
    param->rc.i_aq_mode = X264_AQ_VARIANCE;  // 自适應量化（AQ）模式。 0：關閉AQ
    param->rc.f_aq_strength = 1.0;  // AQ強度，減少平趟和紋理區域的塊效應和模糊度
    param->rc.i_lookahead = 40;  // 決定mbtree向前預測的幀數

    param->rc.b_stat_write = 0;  // 是否将統計資料寫入到檔案psz_stat_out中
    param->rc.psz_stat_out = "x264_2pass.log";
    param->rc.b_stat_read = 0;  // 是否從檔案psz_stat_in中讀入統計資料
    param->rc.psz_stat_in = "x264_2pass.log";
    param->rc.f_qcompress = 0.6;  // 量化曲線(quantizer curve)壓縮因子。
    param->rc.f_qblur = 0.5;  //  時間上模糊量化，減少QP的波動(after curve compression)
    param->rc.f_complexity_blur = 20;  // 時間上模糊複雜性，減少QP的波動(before curve compression)
    param->rc.i_zones = 0;  // number of zone_t's
    param->rc.b_mb_tree = 1;  // 是否開啟基于macroblock-tree的碼控

    /* Log */
    param->pf_log = x264_log_default;  // 日志函數
    param->p_log_private = NULL;
    param->i_log_level = X264_LOG_INFO;  // 日志級别，不需要列印編碼資訊時直接注釋掉即可

    /* */
    param->analyse.intra = X264_ANALYSE_I4x4 | X264_ANALYSE_I8x8; // intra 劃分
    param->analyse.inter = X264_ANALYSE_I4x4 | X264_ANALYSE_I8x8
                         | X264_ANALYSE_PSUB16x16 | X264_ANALYSE_BSUB16x16;  // inter 劃分
    param->analyse.i_direct_mv_pred = X264_DIRECT_PRED_SPATIAL;
    param->analyse.i_me_method = X264_ME_HEX;
    param->analyse.f_psy_rd = 1.0;
    param->analyse.b_psy = 1;
    param->analyse.f_psy_trellis = 0;
    param->analyse.i_me_range = 16;
    param->analyse.i_subpel_refine = 7;
    param->analyse.b_mixed_references = 1;
    param->analyse.b_chroma_me = 1;
    param->analyse.i_mv_range_thread = -1;
    param->analyse.i_mv_range = -1; // set from level_idc
    param->analyse.i_chroma_qp_offset = 0;
    param->analyse.b_fast_pskip = 1;
    param->analyse.b_weighted_bipred = 1;
    param->analyse.i_weighted_pred = X264_WEIGHTP_SMART;
    param->analyse.b_dct_decimate = 1;
    param->analyse.b_transform_8x8 = 1;
    param->analyse.i_trellis = 1;
    param->analyse.i_luma_deadzone[0] = 21;
    param->analyse.i_luma_deadzone[1] = 11;
    param->analyse.b_psnr = 0;
    param->analyse.b_ssim = 0;

    param->i_cqm_preset = X264_CQM_FLAT;
    memset( param->cqm_4iy, 16, sizeof( param->cqm_4iy ) );
    memset( param->cqm_4py, 16, sizeof( param->cqm_4py ) );
    memset( param->cqm_4ic, 16, sizeof( param->cqm_4ic ) );
    memset( param->cqm_4pc, 16, sizeof( param->cqm_4pc ) );
    memset( param->cqm_8iy, 16, sizeof( param->cqm_8iy ) );
    memset( param->cqm_8py, 16, sizeof( param->cqm_8py ) );
    memset( param->cqm_8ic, 16, sizeof( param->cqm_8ic ) );
    memset( param->cqm_8pc, 16, sizeof( param->cqm_8pc ) );

    param->b_repeat_headers = 1;
    param->b_annexb = 1;
    param->b_aud = 0;
    param->b_vfr_input = 1;
    param->i_nal_hrd = X264_NAL_HRD_NONE;
    param->b_tff = 1;
    param->b_pic_struct = 0;
    param->b_fake_interlaced = 0; // 将視訊流标記為交錯(隔行)，哪怕并非為交錯式編碼。可用于編碼藍光相容的25p和30p視訊。預設是未開啟
    param->i_frame_packing = -1;
    param->i_alternative_transfer = 2; /* undef */
    param->b_opencl = 0;
    param->i_opencl_device = 0;
    param->opencl_device_id = NULL;
    param->psz_clbin_file = NULL;
    param->i_avcintra_class = 0;
    param->i_avcintra_flavor = X264_AVCINTRA_FLAVOR_PANASONIC;
}