碼率控制的理論知識：
碼率控制的目的和意義：
圖像通信中碼率控制的目的：通過調節編碼參數，控制單位時間內的編碼視頻流的數據量，以使產生的比特流符合各種應用的需求。視頻壓縮的效率和視頻內容有很大的關系，對于變化多樣的畫面，視頻編碼的輸出的碼流變化較大，在信道環境不好的時候就容易導致解碼端顯示的質量的不穩定。
率失真理論：
由于傳輸帶寬和存儲空間的限制，視頻應用對壓縮比有較高的要求。而無損編碼較低的壓縮比無法滿足視頻在實際應用中的需求。但如果給視頻引入一定程度的失真，通常可以獲得較高的壓縮比。
率失真理論對有損壓縮編碼下的失真和編碼性能之間的關系的描述，為碼率控制的研究提供了堅實的理論依據。率失真理論主旨是描述編碼失真度和編碼數據速率的關系。該理論建立在圖像是連續的基礎上的，在有限數據速率下，由于存在量化誤差，必然存在失真。當使用有損編碼方法時，重建圖像g(x,y)和原始圖像f(x,y)之間存在差異，失真度D的函數形式在理論上是可以根據需要自由選取的，在圖像編碼中，D常用均方差形式表示的，典型的率失真曲線。R(D)為D的凸減函數。
對于怎么選擇哪個函數的率失真效果更好，則是比較哪個函數的率失真函數更為接近典型的率失真函數的曲線。
x264碼率控制方法：采用的碼率控制算法并沒有采用拉格朗日代價函數來控制編碼，而是使用一種更簡單的方法，即利用半精度幀的SATD(sum of absolute transformed difference)作為模式選擇的依據。SATD即將殘差經哈德曼變換的4×4塊的預測殘差絕對值總和，可以將其看作簡單的時頻變換，其值在一定程度上可以反映生成碼流的大小。SATD是將殘差經哈達曼變換4*4塊的預測殘差絕對值總和。自適應宏塊層碼率控制策略：X264的宏塊沒有任何碼率控制的機制，其在幀層得到一個QP后，屬于該幀的所有宏塊都用著統一的QP進行量化。
碼率控制性能測度：
1、比特率誤差|ABR-TBR|/TBR ，越小越好。
2、編碼器性能。
3、緩沖區滿度與TBL的匹配程度。
4、跳幀數。
5、PSNR波動越小越好。
x264中碼率控制的流程(對于重點函數在下面有注釋)：
1.在進行編碼時，Encode--->x264_encoder_open(主要是進行參數的修訂設置，進行初始化)---->x264_ratecontrol_new
2.encode--->Encode_frame--->x264_encoder_encode--->x264_ratecontrol_slice_type
3.encode--->Encode_frame--->x264_encoder_encode--->x264_ratecontrol_start**************
4.encode--->Encode_frame--->x264_encoder_encode--->x264_ratecontrol_qp
5.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(在編完一幀過后)
7.在編完過后，encode--->x264_encoder_close---->ratecontrol summary/x264_ratecontrol_delete
函數注釋：
在編碼中所用的編碼方式：
#define X264_RC_CQP????????????????? 0
#define X264_RC_CRF????????????????? 1
#define X264_RC_ABR????????????????? 2
1.
x264_ratecontrol_new( x264_t *h )
{?? // 獲取RC方式，FPS，bitrate,rc->buffer_rate,rc->buffer_size
// 在碼率控制的時候會出現2pass，參數的初始化
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 )//這里設置mb_tree
{
h->param.rc.f_pb_factor = 1;
rc->qcompress = 1;
}
else
rc->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 )
{
//根據不同類型來獲取不同的qp_constant
h->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 );
這個函數的目的就是在一幀的編碼前就選擇QP
/* Init the rate control */
/* FIXME: Include slice header bit cost. */
x264_ratecontrol_start( h, h->fenc->i_qpplus1, overhead*8 );
對x264_ratecontrol_start函數的解析如下：
x264_zone_t *zone = get_zone( h, h->fenc->i_frame );//找到h->fenc->i_frame所在的zone
....................
//由各種不同的slice類型，vbv等等參數獲取的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;
else
q = rc->qp_constant[ h->sh.i_type ];
if( zone )
{
if( zone->b_force_qp )
q += zone->i_qp - rc->qp_constant[SLICE_TYPE_P];
else
q -= 6*log(zone->f_bitrate_factor)/log(2);
}
//
/* Terminology:
* qp = h.264's 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(即根據所需BIT來計算qscale)
static float rate_estimate_qscale( x264_t *h )
{
//這里是分別針對B，P幀分別進行,因為I幀是已經設定
if( pict_type == SLICE_TYPE_B )
{
//這里B幀的q的大小是由參考幀求的
.....................
.....................
// 由predict_size獲得幀的size
rcc->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幀的q值獲取
else
{
//這里的分有1pass和2pass的選擇
...................
選擇predicted_bits，求出diff
diff = 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 )
{
//這個函數主要是針對一行的bits
if( h->sh.i_type == SLICE_TYPE_B )
{
//由參考的圖像求對應的行的qp，有已編碼的bits獲得此行的bits和qp
int avg_qp = X264_MIN(h->fref0[0]->i_row_qp[y+1], h->fref1[0]->i_row_qp[y+1])
+ 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_offset
i_estimated = row_bits_so_far(h, y);????????????? //FIXME: compute full estimated size
if (i_estimated > h->rc->frame_size_planned)
x264_ratecontrol_set_estimated_size(h, i_estimated);
}
//I, p，這里還要參考緩沖區的狀態
else
{
//對I,P幀在考慮VBV的情況下求的bits和qp
}
}
6.
/* After encoding one frame, save stats and update ratecontrol state */
int x264_ratecontrol_end( x264_t *h, int bits )
{
///統計ipb類型的Mb的個數，并計算平均QP
h->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;
//ABR
if( 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 )///釋放RC開辟的空間
通過以上的流程 總結x264碼率控制的過程基本是有以下三步：
1.對碼率控制的相關變量進行初始化，如，I,P,B的初始QP值，RC的方式，VBV的初始狀態等等；
2.獲取編碼幀的復雜度，x264用SATD表示，對于采用的不同參數的碼率控制的方式，由前面已編碼的Bits,復雜度，目標比特的設置等一些條件來獲取編碼當前幀的qp值。
3.在編碼過程中，由獲得qp值得到預測的bits;
實驗部分：
1.簡單參數設置：
參數設置：
--frames 10 --qp 26 -o test.264 F:\.......\akiyo_qcif.yuv 176x144
其他的參數采用默認設置（在默認設置時采用的碼率控制模型是X264_RC_CQP），所得的實驗結果：
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4189
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 62
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 38
x264 [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:92.08
encoded 10 frames, 24.33 fps, 92.08 kb/s
2.改變碼率控制的模型：
--frames 10 --qp 26 --crf 2 -o test.264 F:\......\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:10.00? size: 10246
x264 [info]: frame P:3???? Avg QP:11.48? size:?? 847
x264 [info]: frame B:6???? Avg QP:12.10? size:?? 172
x264 [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:276.36
encoded 10 frames, 14.27 fps, 276.36 kb/s
針對1，2兩個實驗，所采用的RC模型不一樣，1：X264_RC_CQP，2：X264_RC_CRF，其他參數的設置一樣，從IPB的平均QP，編碼Bits可以看出和對于實際的應用來說，CRF的效果不如CQP。
3.
--frames 10 --qp 26 --pass 1 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile Main, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4068
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 59
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 31
x264 [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:88.58
encoded 10 frames, 52.63 fps, 88.58 kb/s
4.
--frames 10 --qp 26 --pass 2 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4189
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 62
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 38
x264 [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:92.08
encoded 10 frames, 27.70 fps, 92.08 kb/s
5.
--frames 10 --qp 26 --pass 3 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4189
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 62
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 38
x264 [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:92.08
encoded 10 frames, 25.64 fps, 92.08 kb/s
對于3，4，5是關于Pass的實驗比較：
多次壓縮碼率控制
1 ：第一次壓縮，創建統計文件
2 ：按建立的統計文件壓縮并輸出，不覆蓋統計文件，
3 ：按建立的統計文件壓縮，優化統計文件
在想得到建好的效果的時候采用pass 2就可以了。
6.
--frames 10 --qp 26 -- bitrate 64 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:38.31? size:? 1461
x264 [info]: frame P:3???? Avg QP:42.00? size:??? 18
x264 [info]: frame B:6???? Avg QP:45.00? size:??? 14
x264 [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: 31.50
x264 [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:31.94
encoded 10 frames, 31.25 fps, 31.94 kb/s
7.
--frames 250 --qp 26 -- bitrate 64 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:34.62? size:? 1779
x264 [info]: frame P:92??? Avg QP:19.81? size:?? 569
x264 [info]: frame B:157?? Avg QP:26.76? size:??? 53
x264 [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: 18.97
x264 [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:49.92
encoded 250 frames, 16.74 fps, 49.92 kb/s
6，7是針對不同的編碼幀數來進行比較的，在編碼幀數越多，帶寬利用的效果就越好。
6，7是在設置了目標碼率64kp/s時，采用的是ABR的RC模型，在設置了目標碼率能夠根據目標碼率的大小改變QP大小，能夠控制碼率。
碼率控制的目的和意義：
圖像通信中碼率控制的目的：通過調節編碼參數，控制單位時間內的編碼視頻流的數據量，以使產生的比特流符合各種應用的需求。視頻壓縮的效率和視頻內容有很大的關系，對于變化多樣的畫面，視頻編碼的輸出的碼流變化較大，在信道環境不好的時候就容易導致解碼端顯示的質量的不穩定。
率失真理論：
由于傳輸帶寬和存儲空間的限制，視頻應用對壓縮比有較高的要求。而無損編碼較低的壓縮比無法滿足視頻在實際應用中的需求。但如果給視頻引入一定程度的失真，通常可以獲得較高的壓縮比。
率失真理論對有損壓縮編碼下的失真和編碼性能之間的關系的描述，為碼率控制的研究提供了堅實的理論依據。率失真理論主旨是描述編碼失真度和編碼數據速率的關系。該理論建立在圖像是連續的基礎上的，在有限數據速率下，由于存在量化誤差，必然存在失真。當使用有損編碼方法時，重建圖像g(x,y)和原始圖像f(x,y)之間存在差異，失真度D的函數形式在理論上是可以根據需要自由選取的，在圖像編碼中，D常用均方差形式表示的，典型的率失真曲線。R(D)為D的凸減函數。
對于怎么選擇哪個函數的率失真效果更好，則是比較哪個函數的率失真函數更為接近典型的率失真函數的曲線。
x264碼率控制方法：采用的碼率控制算法并沒有采用拉格朗日代價函數來控制編碼，而是使用一種更簡單的方法，即利用半精度幀的SATD(sum of absolute transformed difference)作為模式選擇的依據。SATD即將殘差經哈德曼變換的4×4塊的預測殘差絕對值總和，可以將其看作簡單的時頻變換，其值在一定程度上可以反映生成碼流的大小。SATD是將殘差經哈達曼變換4*4塊的預測殘差絕對值總和。自適應宏塊層碼率控制策略：X264的宏塊沒有任何碼率控制的機制，其在幀層得到一個QP后，屬于該幀的所有宏塊都用著統一的QP進行量化。
碼率控制性能測度：
1、比特率誤差|ABR-TBR|/TBR ，越小越好。
2、編碼器性能。
3、緩沖區滿度與TBL的匹配程度。
4、跳幀數。
5、PSNR波動越小越好。
x264中碼率控制的流程(對于重點函數在下面有注釋)：
1.在進行編碼時，Encode--->x264_encoder_open(主要是進行參數的修訂設置，進行初始化)---->x264_ratecontrol_new
2.encode--->Encode_frame--->x264_encoder_encode--->x264_ratecontrol_slice_type
3.encode--->Encode_frame--->x264_encoder_encode--->x264_ratecontrol_start**************
4.encode--->Encode_frame--->x264_encoder_encode--->x264_ratecontrol_qp
5.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(在編完一幀過后)
7.在編完過后，encode--->x264_encoder_close---->ratecontrol summary/x264_ratecontrol_delete
函數注釋：
在編碼中所用的編碼方式：
#define X264_RC_CQP????????????????? 0
#define X264_RC_CRF????????????????? 1
#define X264_RC_ABR????????????????? 2
1.
x264_ratecontrol_new( x264_t *h )
{?? // 獲取RC方式，FPS，bitrate,rc->buffer_rate,rc->buffer_size
// 在碼率控制的時候會出現2pass，參數的初始化
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 )//這里設置mb_tree
{
h->param.rc.f_pb_factor = 1;
rc->qcompress = 1;
}
else
rc->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 )
{
//根據不同類型來獲取不同的qp_constant
h->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 );
這個函數的目的就是在一幀的編碼前就選擇QP
/* Init the rate control */
/* FIXME: Include slice header bit cost. */
x264_ratecontrol_start( h, h->fenc->i_qpplus1, overhead*8 );
對x264_ratecontrol_start函數的解析如下：
x264_zone_t *zone = get_zone( h, h->fenc->i_frame );//找到h->fenc->i_frame所在的zone
....................
//由各種不同的slice類型，vbv等等參數獲取的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;
else
q = rc->qp_constant[ h->sh.i_type ];
if( zone )
{
if( zone->b_force_qp )
q += zone->i_qp - rc->qp_constant[SLICE_TYPE_P];
else
q -= 6*log(zone->f_bitrate_factor)/log(2);
}
//
/* Terminology:
* qp = h.264's 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(即根據所需BIT來計算qscale)
static float rate_estimate_qscale( x264_t *h )
{
//這里是分別針對B，P幀分別進行,因為I幀是已經設定
if( pict_type == SLICE_TYPE_B )
{
//這里B幀的q的大小是由參考幀求的
.....................
.....................
// 由predict_size獲得幀的size
rcc->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幀的q值獲取
else
{
//這里的分有1pass和2pass的選擇
...................
選擇predicted_bits，求出diff
diff = 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 )
{
//這個函數主要是針對一行的bits
if( h->sh.i_type == SLICE_TYPE_B )
{
//由參考的圖像求對應的行的qp，有已編碼的bits獲得此行的bits和qp
int avg_qp = X264_MIN(h->fref0[0]->i_row_qp[y+1], h->fref1[0]->i_row_qp[y+1])
+ 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_offset
i_estimated = row_bits_so_far(h, y);????????????? //FIXME: compute full estimated size
if (i_estimated > h->rc->frame_size_planned)
x264_ratecontrol_set_estimated_size(h, i_estimated);
}
//I, p，這里還要參考緩沖區的狀態
else
{
//對I,P幀在考慮VBV的情況下求的bits和qp
}
}
6.
/* After encoding one frame, save stats and update ratecontrol state */
int x264_ratecontrol_end( x264_t *h, int bits )
{
///統計ipb類型的Mb的個數，并計算平均QP
h->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;
//ABR
if( 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 )///釋放RC開辟的空間
通過以上的流程 總結x264碼率控制的過程基本是有以下三步：
1.對碼率控制的相關變量進行初始化，如，I,P,B的初始QP值，RC的方式，VBV的初始狀態等等；
2.獲取編碼幀的復雜度，x264用SATD表示，對于采用的不同參數的碼率控制的方式，由前面已編碼的Bits,復雜度，目標比特的設置等一些條件來獲取編碼當前幀的qp值。
3.在編碼過程中，由獲得qp值得到預測的bits;
實驗部分：
1.簡單參數設置：
參數設置：
--frames 10 --qp 26 -o test.264 F:\.......\akiyo_qcif.yuv 176x144
其他的參數采用默認設置（在默認設置時采用的碼率控制模型是X264_RC_CQP），所得的實驗結果：
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4189
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 62
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 38
x264 [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:92.08
encoded 10 frames, 24.33 fps, 92.08 kb/s
2.改變碼率控制的模型：
--frames 10 --qp 26 --crf 2 -o test.264 F:\......\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:10.00? size: 10246
x264 [info]: frame P:3???? Avg QP:11.48? size:?? 847
x264 [info]: frame B:6???? Avg QP:12.10? size:?? 172
x264 [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:276.36
encoded 10 frames, 14.27 fps, 276.36 kb/s
針對1，2兩個實驗，所采用的RC模型不一樣，1：X264_RC_CQP，2：X264_RC_CRF，其他參數的設置一樣，從IPB的平均QP，編碼Bits可以看出和對于實際的應用來說，CRF的效果不如CQP。
3.
--frames 10 --qp 26 --pass 1 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile Main, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4068
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 59
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 31
x264 [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:88.58
encoded 10 frames, 52.63 fps, 88.58 kb/s
4.
--frames 10 --qp 26 --pass 2 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4189
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 62
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 38
x264 [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:92.08
encoded 10 frames, 27.70 fps, 92.08 kb/s
5.
--frames 10 --qp 26 --pass 3 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:23.00? size:? 4189
x264 [info]: frame P:3???? Avg QP:26.00? size:??? 62
x264 [info]: frame B:6???? Avg QP:28.00? size:??? 38
x264 [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:92.08
encoded 10 frames, 25.64 fps, 92.08 kb/s
對于3，4，5是關于Pass的實驗比較：
多次壓縮碼率控制
1 ：第一次壓縮，創建統計文件
2 ：按建立的統計文件壓縮并輸出，不覆蓋統計文件，
3 ：按建立的統計文件壓縮，優化統計文件
在想得到建好的效果的時候采用pass 2就可以了。
6.
--frames 10 --qp 26 -- bitrate 64 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:38.31? size:? 1461
x264 [info]: frame P:3???? Avg QP:42.00? size:??? 18
x264 [info]: frame B:6???? Avg QP:45.00? size:??? 14
x264 [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: 31.50
x264 [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:31.94
encoded 10 frames, 31.25 fps, 31.94 kb/s
7.
--frames 250 --qp 26 -- bitrate 64 -o test.264 F:\.....\bin\akiyo_qcif.yuv 176x144
x264 [info]: 176x144 @ 25.00 fps
x264 [info]: using cpu capabilities: MMX2 SSE2 Cache64 Slow_mod4_stack
x264 [info]: profile High, level 1.1
x264 [info]: frame I:1???? Avg QP:34.62? size:? 1779
x264 [info]: frame P:92??? Avg QP:19.81? size:?? 569
x264 [info]: frame B:157?? Avg QP:26.76? size:??? 53
x264 [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: 18.97
x264 [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:49.92
encoded 250 frames, 16.74 fps, 49.92 kb/s
6，7是針對不同的編碼幀數來進行比較的，在編碼幀數越多，帶寬利用的效果就越好。
6，7是在設置了目標碼率64kp/s時，采用的是ABR的RC模型，在設置了目標碼率能夠根據目標碼率的大小改變QP大小，能夠控制碼率。
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