摄影协会网站源码,wordpress ie8,wordpress仿微信公众号模板下载,企业网站建设方案书范本码率控制的理论知识#xff1a;码率控制的目的和意义#xff1a;图像通信中码率控制的目的#xff1a;通过调节编码参数#xff0c;控制单位时间内的编码视频流的数据量#xff0c;以使产生的比特流符合各种应用的需求。视频压缩的效率和视频内容有很大的关系#xff0c;…码率控制的理论知识码率控制的目的和意义图像通信中码率控制的目的通过调节编码参数控制单位时间内的编码视频流的数据量以使产生的比特流符合各种应用的需求。视频压缩的效率和视频内容有很大的关系对于变化多样的画面视频编码的输出的码流变化较大在信道环境不好的时候就容易导致解码端显示的质量的不稳定。率失真理论由于传输带宽和存储空间的限制视频应用对压缩比有较高的要求。而无损编码较低的压缩比无法满足视频在实际应用中的需求。但如果给视频引入一定程度的失真通常可以获得较高的压缩比。率失真理论对有损压缩编码下的失真和编码性能之间的关系的描述为码率控制的研究提供了坚实的理论依据。率失真理论主旨是描述编码失真度和编码数据速率的关系。该理论建立在图像是连续的基础上的在有限数据速率下由于存在量化误差必然存在失真。当使用有损编码方法时重建图像g(x,y)和原始图像f(x,y)之间存在差异失真度D的函数形式在理论上是可以根据需要自由选取的在图像编码中D常用均方差形式表示的典型的率失真曲线。R(D)为D的凸减函数。对于怎么选择哪个函数的率失真效果更好则是比较哪个函数的率失真函数更为接近典型的率失真函数的曲线。x264码率控制方法采用的码率控制算法并没有采用拉格朗日代价函数来控制编码而是使用一种更简单的方法即利用半精度帧的SATD(sum of absolute transformed difference)作为模式选择的依据。SATD即将残差经哈德曼变换的4×4块的预测残差绝对值总和可以将其看作简单的时频变换其值在一定程度上可以反映生成码流的大小。SATD是将残差经哈达曼变换4*4块的预测残差绝对值总和。自适应宏块层码率控制策略X264的宏块没有任何码率控制的机制其在帧层得到一个QP后属于该帧的所有宏块都用着统一的QP进行量化。码率控制性能测度1、比特率误差|ABR-TBR|/TBR 越小越好。2、编码器性能。3、缓冲区满度与TBL的匹配程度。4、跳帧数。5、PSNR波动越小越好。x264中码率控制的流程(对于重点函数在下面有注释)1.在进行编码时Encode---x264_encoder_open(主要是进行参数的修订设置进行初始化)----x264_ratecontrol_new2.encode---Encode_frame---x264_encoder_encode---x264_ratecontrol_slice_type3.encode---Encode_frame---x264_encoder_encode---x264_ratecontrol_start**************4.encode---Encode_frame---x264_encoder_encode---x264_ratecontrol_qp5.encode---Encode_frame---x264_encoder_encode---x264_slices_write---x264_slice_write---x264_ratecontrol_mb********************6.encode---Encode_frame---x264_encoder_encode---x264_ratecontrol_end(在编完一帧过后)7.在编完过后encode---x264_encoder_close----ratecontrol summary/x264_ratecontrol_delete函数注释在编码中所用的编码方式#define X264_RC_CQP 0#define X264_RC_CRF 1#define X264_RC_ABR 21.x264_ratecontrol_new( x264_t *h ){ // 获取RC方式FPSbitrate,rc-buffer_rate,rc-buffer_size// 在码率控制的时候会出现2pass参数的初始化rc h-rc;rc-b_abr h-param.rc.i_rc_method ! X264_RC_CQP !h-param.rc.b_stat_read;rc-b_2pass h-param.rc.i_rc_method X264_RC_ABR h-param.rc.b_stat_read;..........if( h-param.rc.b_mb_tree )//这里设置mb_tree{h-param.rc.f_pb_factor 1;rc-qcompress 1;}elserc-qcompress h-param.rc.f_qcompress;..............rc-ip_offset 6.0 * log(h-param.rc.f_ip_factor) / log(2.0);rc-pb_offset 6.0 * log(h-param.rc.f_pb_factor) / log(2.0);rc-qp_constant[SLICE_TYPE_P] h-param.rc.i_qp_constant;rc-qp_constant[SLICE_TYPE_I] x264_clip3( h-param.rc.i_qp_constant - rc-ip_offset 0.5, 0, 51 );rc-qp_constant[SLICE_TYPE_B] x264_clip3( h-param.rc.i_qp_constant rc-pb_offset 0.5, 0, 51 );}2.int x264_ratecontrol_slice_type( x264_t *h, int frame_num ){//根据不同类型来获取不同的qp_constanth-param.rc.i_qp_constant (h-stat.i_frame_count[SLICE_TYPE_P] 0) ? 24: 1 h-stat.f_frame_qp[SLICE_TYPE_P] / h-stat.i_frame_count[SLICE_TYPE_P];rc-qp_constant[SLICE_TYPE_P] x264_clip3( h-param.rc.i_qp_constant, 0, 51 );rc-qp_constant[SLICE_TYPE_I] x264_clip3( (int)( qscale2qp( qp2qscale( h-param.rc.i_qp_constant ) / fabs( h-param.rc.f_ip_factor )) 0.5 ), 0, 51 );rc-qp_constant[SLICE_TYPE_B] x264_clip3( (int)( qscale2qp( qp2qscale( h-param.rc.i_qp_constant ) * fabs( h-param.rc.f_pb_factor )) 0.5 ), 0, 51 );}3.x264_ratecontrol_start( h, h-fenc-i_qpplus1, overhead*8 );这个函数的目的就是在一帧的编码前就选择QP/* Init the rate control *//* FIXME: Include slice header bit cost. */x264_ratecontrol_start( h, h-fenc-i_qpplus1, overhead*8 );对x264_ratecontrol_start函数的解析如下x264_zone_t *zone get_zone( h, h-fenc-i_frame );//找到h-fenc-i_frame所在的zone....................//由各种不同的slice类型vbv等等参数获取的q值if( i_force_qp ){q i_force_qp - 1;//}else if( rc-b_abr ){q qscale2qp( rate_estimate_qscale( h ) );//下面有注解}else if( rc-b_2pass ){rce-new_qscale rate_estimate_qscale( h );q qscale2qp( rce-new_qscale );}else /* CQP */{if( h-sh.i_type SLICE_TYPE_B h-fdec-b_kept_as_ref )q ( rc-qp_constant[ SLICE_TYPE_B ] rc-qp_constant[ SLICE_TYPE_P ] ) / 2;elseq rc-qp_constant[ h-sh.i_type ];if( zone ){if( zone-b_force_qp )q zone-i_qp - rc-qp_constant[SLICE_TYPE_P];elseq - 6*log(zone-f_bitrate_factor)/log(2);}///* Terminology:* qp h.264s quantizer* qscale linearized quantizer Lagrange multiplier*/static inline double qp2qscale(double qp){return 0.85 * pow(2.0, ( qp - 12.0 ) / 6.0);}static inline double qscale2qp(double qscale){return 12.0 6.0 * log(qscale/0.85) / log(2.0);}rate_estimate_qscale( h )// update qscale for 1 frame based on actual bits used so far(即根据所需BIT来计算qscale)static float rate_estimate_qscale( x264_t *h ){//这里是分别针对BP帧分别进行,因为I帧是已经设定if( pict_type SLICE_TYPE_B ){//这里B帧的q的大小是由参考帧求的..........................................// 由predict_size获得帧的sizercc-frame_size_planned predict_size( rcc-pred_b_from_p, q, h-fref1[h-i_ref1-1]-i_satd );x264_ratecontrol_set_estimated_size(h, rcc-frame_size_planned);//void x264_ratecontrol_set_estimated_size( x264_t *h, int bits ){x264_pthread_mutex_lock( h-fenc-mutex );h-rc-frame_size_estimated bits;///***********x264_pthread_mutex_unlock( h-fenc-mutex );}}P帧的q值获取else{//这里的分有1pass和2pass的选择...................选择predicted_bits求出diffdiff predicted_bits - (int64_t)rce.expected_bits;q / x264_clip3f((double)(abr_buffer - diff) / abr_buffer, .5, 2);}}4.int x264_ratecontrol_qp( x264_t *h ){return h-rc-qpm;}5.void x264_ratecontrol_mb( x264_t *h, int bits ){//这个函数主要是针对一行的bitsif( h-sh.i_type SLICE_TYPE_B ){//由参考的图像求对应的行的qp有已编码的bits获得此行的bits和qpint avg_qp X264_MIN(h-fref0[0]-i_row_qp[y1], h-fref1[0]-i_row_qp[y1])rc-pb_offset * ((h-fenc-i_type X264_TYPE_BREF) ? 0.5 : 1);rc-qpm X264_MIN(X264_MAX( rc-qp, avg_qp), 51); //avg_qp could go higher than 51 due to pb_offseti_estimated row_bits_so_far(h, y); //FIXME: compute full estimated sizeif (i_estimated h-rc-frame_size_planned)x264_ratecontrol_set_estimated_size(h, i_estimated);}//I, p这里还要参考缓冲区的状态else{//对I,P帧在考虑VBV的情况下求的bits和qp}}6./* After encoding one frame, save stats and update ratecontrol state */int x264_ratecontrol_end( x264_t *h, int bits ){///统计ipb类型的Mb的个数并计算平均QPh-fdec-f_qp_avg_rc rc-qpa_rc / h-mb.i_mb_count;h-fdec-f_qp_avg_aq rc-qpa_aq / h-mb.i_mb_count;}7.void x264_ratecontrol_summary( x264_t *h ){x264_ratecontrol_t *rc h-rc;//ABRif( rc-b_abr h-param.rc.i_rc_method X264_RC_ABR rc-cbr_decay .9999 ){double base_cplx h-mb.i_mb_count * (h-param.i_bframe ? 120 : 80);double mbtree_offset h-param.rc.b_mb_tree ? (1.0-h-param.rc.f_qcompress)*13.5 : 0;x264_log( h, X264_LOG_INFO, final ratefactor: %.2f\n,qscale2qp( pow( base_cplx, 1 - rc-qcompress )* rc-cplxr_sum / rc-wanted_bits_window ) - mbtree_offset );}}/void x264_ratecontrol_delete( x264_t *h )///释放RC开辟的空间通过以上的流程
总结x264码率控制的过程基本是有以下三步1.对码率控制的相关变量进行初始化如I,P,B的初始QP值RC的方式VBV的初始状态等等2.获取编码帧的复杂度x264用SATD表示对于采用的不同参数的码率控制的方式由前面已编码的Bits,复杂度目标比特的设置等一些条件来获取编码当前帧的qp值。3.在编码过程中由获得qp值得到预测的bits;实验部分1.简单参数设置参数设置--frames 10 --qp 26 -o test.264 F:\.......\akiyo_qcif.yuv 176x144其他的参数采用默认设置在默认设置时采用的码率控制模型是X264_RC_CQP所得的实验结果x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile High, level 1.1x264 [info]: frame I:1 Avg QP:23.00 size: 4189x264 [info]: frame P:3 Avg QP:26.00 size: 62x264 [info]: frame B:6 Avg QP:28.00 size: 38x264 [info]: consecutive B-frames: 11.1% 0.0% 0.0% 88.9%x264 [info]: mb I I16..4: 3.0% 41.4% 55.6%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 3.0% 1.3% 1.7% 0.0% 0.0% skip:93.9%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 4.4% 0.2% 0.3% direct:0.7% skip:94.4% L0:56.0% L1:40.5% BI: 3.4%x264 [info]: 8x8 transform intra:41.4% inter:25.9%x264 [info]: coded y,uvDC,uvAC intra: 83.6% 81.8% 68.7% inter: 1.1% 0.1% 0.0%x264 [info]: i16 v,h,dc,p: 100% 0% 0% 0%x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 30% 15% 4% 4% 4% 7% 5% 6%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 35% 18% 8% 5% 5% 10% 5% 8% 6%x264 [info]: ref P L0: 88.9% 0.0% 11.1%x264 [info]: kb/s:92.08encoded 10 frames, 24.33 fps, 92.08 kb/s2.改变码率控制的模型--frames 10 --qp 26 --crf 2 -o test.264 F:\......\akiyo_qcif.yuv 176x144x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile High, level 1.1x264 [info]: frame I:1 Avg QP:10.00 size: 10246x264 [info]: frame P:3 Avg QP:11.48 size: 847x264 [info]: frame B:6 Avg QP:12.10 size: 172x264 [info]: consecutive B-frames: 11.1% 0.0% 0.0% 88.9%x264 [info]: mb I I16..4: 1.0% 44.4% 54.5%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 30.0% 3.0% 4.7% 0.0% 0.0% skip:62.3%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 6.9% 1.0% 1.2% direct:4.0% skip:86.9% L0:34.7% L1:55.6% BI: 9.7%x264 [info]: 8x8 transform intra:44.4% inter:34.8%x264 [info]: coded y,uvDC,uvAC intra: 100.0% 99.0% 94.9% inter: 11.6% 7.6% 4.9%x264 [info]: i16 v,h,dc,p: 100% 0% 0% 0%x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 30% 33% 16% 3% 2% 3% 4% 4% 5%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 28% 12% 11% 5% 7% 11% 6% 12% 8%x264 [info]: ref P L0: 95.8% 1.6% 2.7%x264 [info]: ref B L0: 96.3% 3.7%x264 [info]: kb/s:276.36encoded 10 frames, 14.27 fps, 276.36 kb/s针对12两个实验所采用的RC模型不一样1X264_RC_CQP2X264_RC_CRF其他参数的设置一样从IPB的平均QP编码Bits可以看出和对于实际的应用来说CRF的效果不如CQP。3.--frames 10 --qp 26 --pass 1 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile Main, level 1.1x264 [info]: frame I:1 Avg QP:23.00 size: 4068x264 [info]: frame P:3 Avg QP:26.00 size: 59x264 [info]: frame B:6 Avg QP:28.00 size: 31x264 [info]: consecutive B-frames: 11.1% 0.0% 0.0% 88.9%x264 [info]: mb I I16..4: 15.2% 0.0% 84.8%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 7.1% 0.0% 0.0% 0.0% 0.0% skip:92.9%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 1.2% 0.0% 0.0% direct:1.5% skip:97.3% L0:100.0% L1: 0.0% BI: 0.0%x264 [info]: coded y,uvDC,uvAC intra: 87.4% 77.8% 68.7% inter: 1.1% 0.1% 0.0%x264 [info]: i16 v,h,dc,p: 47% 20% 27% 7%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 29% 27% 10% 5% 4% 8% 5% 6% 5%x264 [info]: kb/s:88.58encoded 10 frames, 52.63 fps, 88.58 kb/s4.--frames 10 --qp 26 --pass 2 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile High, level 1.1x264 [info]: frame I:1 Avg QP:23.00 size: 4189x264 [info]: frame P:3 Avg QP:26.00 size: 62x264 [info]: frame B:6 Avg QP:28.00 size: 38x264 [info]: consecutive B-frames: 11.1% 0.0% 0.0% 88.9%x264 [info]: mb I I16..4: 3.0% 41.4% 55.6%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 3.0% 1.3% 1.7% 0.0% 0.0% skip:93.9%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 4.4% 0.2% 0.3% direct:0.7% skip:94.4% L0:56.0% L1:40.5% BI: 3.4%x264 [info]: 8x8 transform intra:41.4% inter:25.9%x264 [info]: coded y,uvDC,uvAC intra: 83.6% 81.8% 68.7% inter: 1.1% 0.1% 0.0%x264 [info]: i16 v,h,dc,p: 100% 0% 0% 0%x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 30% 15% 4% 4% 4% 7% 5% 6%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 35% 18% 8% 5% 5% 10% 5% 8% 6%x264 [info]: ref P L0: 88.9% 0.0% 11.1%x264 [info]: kb/s:92.08encoded 10 frames, 27.70 fps, 92.08 kb/s5.--frames 10 --qp 26 --pass 3 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile High, level 1.1x264 [info]: frame I:1 Avg QP:23.00 size: 4189x264 [info]: frame P:3 Avg QP:26.00 size: 62x264 [info]: frame B:6 Avg QP:28.00 size: 38x264 [info]: consecutive B-frames: 11.1% 0.0% 0.0% 88.9%x264 [info]: mb I I16..4: 3.0% 41.4% 55.6%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 3.0% 1.3% 1.7% 0.0% 0.0% skip:93.9%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 4.4% 0.2% 0.3% direct:0.7% skip:94.4% L0:56.0% L1:40.5% BI: 3.4%x264 [info]: 8x8 transform intra:41.4% inter:25.9%x264 [info]: coded y,uvDC,uvAC intra: 83.6% 81.8% 68.7% inter: 1.1% 0.1% 0.0%x264 [info]: i16 v,h,dc,p: 100% 0% 0% 0%x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 30% 15% 4% 4% 4% 7% 5% 6%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 35% 18% 8% 5% 5% 10% 5% 8% 6%x264 [info]: ref P L0: 88.9% 0.0% 11.1%x264 [info]: kb/s:92.08encoded 10 frames, 25.64 fps, 92.08 kb/s对于345是关于Pass的实验比较多次压缩码率控制1
第一次压缩创建统计文件2
按建立的统计文件压缩并输出不覆盖统计文件3
按建立的统计文件压缩优化统计文件在想得到建好的效果的时候采用pass 2就可以了。 6.--frames 10 --qp 26 --
bitrate 64 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile High, level 1.1x264 [info]: frame I:1 Avg QP:38.31 size: 1461x264 [info]: frame P:3 Avg QP:42.00 size: 18x264 [info]: frame B:6 Avg QP:45.00 size: 14x264 [info]: consecutive B-frames: 11.1% 0.0% 0.0% 88.9%x264 [info]: mb I I16..4: 15.2% 68.7% 16.2%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 2.0% 0.0% 0.3% 0.0% 0.0% skip:97.6%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 0.2% 0.0% 0.0% direct:0.0% skip:99.8% L0: 0.0% L1:100.0% BI: 0.0%x264 [info]: final ratefactor: 31.50x264 [info]: 8x8 transform intra:68.7%x264 [info]: coded y,uvDC,uvAC intra: 48.0% 61.6% 32.3% inter: 0.0% 0.0% 0.0%x264 [info]: i16 v,h,dc,p: 33% 47% 7% 13%x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 35% 17% 20% 3% 4% 7% 3% 7% 5%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 50% 14% 8% 5% 5% 5% 3% 6% 4%x264 [info]: kb/s:31.94encoded 10 frames, 31.25 fps, 31.94 kb/s7.--frames 250 --qp 26 --
bitrate 64 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144x264 [info]: 176x144 25.00 fpsx264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stackx264 [info]: profile High, level 1.1x264 [info]: frame I:1 Avg QP:34.62 size: 1779x264 [info]: frame P:92 Avg QP:19.81 size: 569x264 [info]: frame B:157 Avg QP:26.76 size: 53x264 [info]: consecutive B-frames: 15.7% 0.0% 2.4% 81.9%x264 [info]: mb I I16..4: 14.1% 61.6% 24.2%x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 25.8% 9.4% 9.9% 0.0% 0.0% skip:54.8%x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 13.9% 0.7% 1.4% direct:1.1% skip:83.0% L0:16.6% L1:72.1% BI:11.3%x264 [info]: final ratefactor: 18.97x264 [info]: 8x8 transform intra:61.5% inter:40.4%x264 [info]: coded y,uvDC,uvAC intra: 61.3% 65.4% 34.6% inter: 8.6% 6.8% 2.8%x264 [info]: i16 v,h,dc,p: 57% 43% 0% 0%x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 32% 22% 18% 4% 2% 7% 3% 7% 4%x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 45% 10% 10% 5% 6% 7% 6% 6% 5%x264 [info]: ref P L0: 87.6% 7.6% 4.8%x264 [info]: ref B L0: 95.0% 5.0%x264 [info]: kb/s:49.92encoded 250 frames, 16.74 fps, 49.92 kb/s67是针对不同的编码帧数来进行比较的在编码帧数越多带宽利用的效果就越好。67是在设置了目标码率64kp/s时采用的是ABR的RC模型在设置了目标码率能够根据目标码率的大小改变QP大小能够控制码率。
