x264參數配置-preset

x264中preset等級有10個，表示編碼速度的快慢。
相比tune，preset主要調節lookahead長度、參考幀列表幀數量、可用宏塊劃分模式、運動搜索方法、運動搜索窗口、下采樣質量、是否使用B幀、是否自適應B幀、連續B幀數量、權重預測方法、direct方法、trellis量化、是否子塊獨立參考幀等

static const char * const x264_preset_names[] = { 
"ultrafast", "superfast",  "veryfast", 
 "faster",  "fast",  "medium",  "slow", 
 "slower",  "veryslow",   "placebo", 0 };

ultrafast

 if( !strcasecmp( preset, "ultrafast" ) )	//特快
    {
        param->i_frame_reference = 1;		//參考幀數量1
        param->i_scenecut_threshold = 0;	//不使用場景切換判斷
        param->b_deblocking_filter = 0;		//關閉環路濾波
        param->b_cabac = 0;					//使用cavlc
        param->i_bframe = 0;				//不適用B幀
        param->analyse.intra = 0;			//不允許intra子塊劃分，只能能有16x16
        param->analyse.inter = 0;			//不允許inter子塊劃分，只能有16x16和skip
        param->analyse.b_transform_8x8 = 0;			//不使用8x8dct
        param->analyse.i_me_method = X264_ME_DIA;	//菱形搜索運動估計
        param->analyse.i_subpel_refine = 0;			//不允許下采樣運動搜索
        param->rc.i_aq_mode = 0;					//不使用adaptive qp
        param->analyse.b_mixed_references = 0;		//不允許宏塊各劃分子塊獨立參考
        param->i_bframe_adaptive = X264_B_ADAPT_NONE;//不使用B幀自適應
        param->rc.b_mb_tree = 0;					//不使用宏塊樹
        param->analyse.i_weighted_pred = X264_WEIGHTP_NONE;//
        param->analyse.b_weighted_bipred = 0;
        param->rc.i_lookahead = 0;					//碼控lookahead隊列大小0
    }

superfast

    else if( !strcasecmp( preset, "superfast" ) )	//超快
    {
		//這間參考只允許intra8x8和intra4x4
        param->analyse.inter = X264_ANALYSE_I8x8|X264_ANALYSE_I4x4;
        param->analyse.i_me_method = X264_ME_DIA;	//鑽石搜索
        param->analyse.i_subpel_refine = 1;			//允許下采樣運動搜索
        param->i_frame_reference = 1;				//參考幀列表1幀
        param->analyse.b_mixed_references = 0;		//不允許宏塊各劃分子塊獨立參考
        param->analyse.i_trellis = 0;				//不適用trellis量化
        param->rc.b_mb_tree = 0;					//不允許宏塊樹
        param->analyse.i_weighted_pred = X264_WEIGHTP_SIMPLE;//P幀權重預測
        param->rc.i_lookahead = 0;					//lookahead隊列長度0
    }

veryfast

    else if( !strcasecmp( preset, "veryfast" ) )
    {
        param->analyse.i_subpel_refine = 2;			//下采樣進度2
        param->i_frame_reference = 1;				//參考幀列表1幀
        param->analyse.b_mixed_references = 0;		//不允許宏塊各劃分子塊獨立參考幀
        param->analyse.i_trellis = 0;				//不適用trellis量化
        param->analyse.i_weighted_pred = X264_WEIGHTP_SIMPLE;//P幀權重預測
        param->rc.i_lookahead = 10;					//lookahead隊列長度10
    }

faster

    else if( !strcasecmp( preset, "faster" ) )
    {
        param->analyse.b_mixed_references = 0;	//不允許宏塊各劃分子塊獨立參考幀
        param->i_frame_reference = 2;			//參考幀列表2幀
        param->analyse.i_subpel_refine = 4;		//下采樣精度4
        param->analyse.i_weighted_pred = X264_WEIGHTP_SIMPLE;//P幀權重預測simple
        param->rc.i_lookahead = 20;			//lookahead隊列長度20
    }

fast

    else if( !strcasecmp( preset, "fast" ) )
    {
        param->i_frame_reference = 2;		//參考幀列表2幀
        param->analyse.i_subpel_refine = 6;	//下采樣質量6
        param->analyse.i_weighted_pred = X264_WEIGHTP_SIMPLE;//P幀權重預測simple
        param->rc.i_lookahead = 30;		//lookahead隊列30幀
    }

medium

    else if( !strcasecmp( preset, "medium" ) )
    {
        /* Default is medium 
		   默認即medium */
    }

slow

    else if( !strcasecmp( preset, "slow" ) )
    {
        param->analyse.i_subpel_refine = 8;//下采樣質量8
        param->i_frame_reference = 5;	//參考幀列表最多5幀
        param->analyse.i_direct_mv_pred = X264_DIRECT_PRED_AUTO;//direct預測模式自動
        param->analyse.i_trellis = 2;	//trellis量化 2
        param->rc.i_lookahead = 50;		//lookhead隊列50幀
    }

slower

    else if( !strcasecmp( preset, "slower" ) )
    {
        param->analyse.i_me_method = X264_ME_UMH;	//運動搜索方法爲非對稱十字六邊形網絡搜索
        param->analyse.i_subpel_refine = 9;		//下采樣質量9
        param->i_frame_reference = 8;		//參考幀列表8幀
        param->i_bframe_adaptive = X264_B_ADAPT_TRELLIS;//使用viterbi最優路徑自適應決定B幀
        param->analyse.i_direct_mv_pred = X264_DIRECT_PRED_AUTO;
        param->analyse.inter |= X264_ANALYSE_PSUB8x8;	//允許低於8x8的inter，即8x4，4x8，4x4
        param->analyse.i_trellis = 2;					//trellis量化 2
        param->rc.i_lookahead = 60;				//lookahead隊列60幀
    }

veryslow

    else if( !strcasecmp( preset, "veryslow" ) )
    {
        param->analyse.i_me_method = X264_ME_UMH;//運動搜索方法爲非對稱十字六邊形網絡搜索
        param->analyse.i_subpel_refine = 10;	//下采樣質量10
        param->analyse.i_me_range = 24;		//運動搜索範圍24像素
        param->i_frame_reference = 16;		//參考幀列表16幀
        param->i_bframe_adaptive = X264_B_ADAPT_TRELLIS;	//使用viterbi最優路徑自適應決定B幀
        param->analyse.i_direct_mv_pred = X264_DIRECT_PRED_AUTO;//direct預測模式自動
        param->analyse.inter |= X264_ANALYSE_PSUB8x8;	//允許低於8x8的inter，即8x4，4x8，4x4
        param->analyse.i_trellis = 2;			//trellis量化 2
        param->i_bframe = 8;					//允許最多個連續B幀
        param->rc.i_lookahead = 60;				//lookahead隊列60幀
    }

placebo

    else if( !strcasecmp( preset, "placebo" ) )
    {
        param->analyse.i_me_method = X264_ME_TESA;	//運動估計方法爲TESA
        param->analyse.i_subpel_refine = 11;	//下采樣運動估計質量11
        param->analyse.i_me_range = 24;			//整像素運動搜索範圍
        param->i_frame_reference = 16;			//參考幀數量16
        param->i_bframe_adaptive = X264_B_ADAPT_TRELLIS;	//自適應B幀TRELLIS方法
        param->analyse.i_direct_mv_pred = X264_DIRECT_PRED_AUTO;//direct預測模式自動
        param->analyse.inter |= X264_ANALYSE_PSUB8x8;	//允許低於8x8的inter，即8x4，4x8，4x4
        param->analyse.b_fast_pskip = 0;		//關閉快速pskip決定
        param->analyse.i_trellis = 2;			//trellis量化 2
        param->i_bframe = 16;					//允許最多16個連續B幀
        param->rc.i_lookahead = 60;				//lookahead隊列60幀
    }