x264代码剖析（十四）：核心算法之宏块编码函数x264_macroblock_encode()

宏块编码函数x264_macroblock_encode()是完成变换与量化的主要函数，而x264_macroblock_encode()调用了x264_macroblock_encode_internal()函数，在x264_macroblock_encode_internal()函数中，主要完成了如下功能：

x264_macroblock_encode_skip()：编码Skip类型宏块。

x264_mb_encode_i16x16()：编码Intra16x16类型的宏块。该函数除了进行DCT变换之外，还对16个小块的DC系数进行了Hadamard变换。

x264_mb_encode_i4x4()：编码Intra4x4类型的宏块。

帧间宏块编码：这一部分代码直接写在了函数体里面。

x264_mb_encode_chroma()：编码色度块。

x264_macroblock_encode()函数与x264_macroblock_encode_internal()函数都处于encoder文件夹内的macroblock.c中，其调用关系图如下所示：

1、x264_macroblock_encode()函数

x264_macroblock_encode()函数处于encoder文件夹内的macroblock.c中，x264_macroblock_encode()封装了x264_macroblock_encode_internal()。如果色度模式是YUV444的话，传递的参数plane_count=3而chroma=0；如果不是YUV444的话，传递的参数plane_count=1而chroma=1。

对应的代码如下：

/******************************************************************/
/******************************************************************/
/*
======Analysed by RuiDong Fang
======Csdn Blog:http://blog.csdn.net/frd2009041510
======Date:2016.03.22*/
/******************************************************************/
/******************************************************************//************====== 宏块编码函数x264_macroblock_encode() ======************/
/*
功能：x264_macroblock_encode()封装了x264_macroblock_encode_internal(),即编码的内部函数——残差DCT变换、量化
*/
void x264_macroblock_encode( x264_t *h )
{if( CHROMA444 )x264_macroblock_encode_internal( h, 3, 0 );//YUV444相当于把YUV3个分量都当做Y编码elsex264_macroblock_encode_internal( h, 1, 1 );
}

2、x264_macroblock_encode_internal()函数

x264_macroblock_encode_internal()函数也处于encoder文件夹内的macroblock.c中，具体的代码分析如下：

/************====== 宏块编码函数x264_macroblock_encode_internal() ======************/
/*
功能：调用了编码-残差DCT变换、量化-内部函数
*/
/****************************************************************************** x264_macroblock_encode:*****************************************************************************/
static ALWAYS_INLINE void x264_macroblock_encode_internal( x264_t *h, int plane_count, int chroma )
{int i_qp = h->mb.i_qp;int b_decimate = h->mb.b_dct_decimate;int b_force_no_skip = 0;int nz;h->mb.i_cbp_luma = 0;for( int p = 0; p < plane_count; p++ )h->mb.cache.non_zero_count[x264_scan8[LUMA_DC+p]] = 0;/*======== PCM ========*/if( h->mb.i_type == I_PCM )//PCM{/* if PCM is chosen, we need to store reconstructed frame data */for( int p = 0; p < plane_count; p++ )h->mc.copy[PIXEL_16x16]( h->mb.pic.p_fdec[p], FDEC_STRIDE, h->mb.pic.p_fenc[p], FENC_STRIDE, 16 );if( chroma ){int height = 16 >> CHROMA_V_SHIFT;h->mc.copy[PIXEL_8x8]  ( h->mb.pic.p_fdec[1], FDEC_STRIDE, h->mb.pic.p_fenc[1], FENC_STRIDE, height );h->mc.copy[PIXEL_8x8]  ( h->mb.pic.p_fdec[2], FDEC_STRIDE, h->mb.pic.p_fenc[2], FENC_STRIDE, height );}return;}if( !h->mb.b_allow_skip ){b_force_no_skip = 1;if( IS_SKIP(h->mb.i_type) ){if( h->mb.i_type == P_SKIP )h->mb.i_type = P_L0;else if( h->mb.i_type == B_SKIP )h->mb.i_type = B_DIRECT;}}//根据不同的宏块类型，进行编码/*======== P-skip ========*/if( h->mb.i_type == P_SKIP ){/* don't do pskip motion compensation if it was already done in macroblock_analyse */if( !h->mb.b_skip_mc ){int mvx = x264_clip3( h->mb.cache.mv[0][x264_scan8[0]][0],h->mb.mv_min[0], h->mb.mv_max[0] );int mvy = x264_clip3( h->mb.cache.mv[0][x264_scan8[0]][1],h->mb.mv_min[1], h->mb.mv_max[1] );for( int p = 0; p < plane_count; p++ )h->mc.mc_luma( h->mb.pic.p_fdec[p], FDEC_STRIDE,&h->mb.pic.p_fref[0][0][p*4], h->mb.pic.i_stride[p],mvx, mvy, 16, 16, &h->sh.weight[0][p] );if( chroma ){int v_shift = CHROMA_V_SHIFT;int height = 16 >> v_shift;/* Special case for mv0, which is (of course) very common in P-skip mode. */if( mvx | mvy )h->mc.mc_chroma( h->mb.pic.p_fdec[1], h->mb.pic.p_fdec[2], FDEC_STRIDE,h->mb.pic.p_fref[0][0][4], h->mb.pic.i_stride[1],mvx, 2*mvy>>v_shift, 8, height );elseh->mc.load_deinterleave_chroma_fdec( h->mb.pic.p_fdec[1], h->mb.pic.p_fref[0][0][4],h->mb.pic.i_stride[1], height );if( h->sh.weight[0][1].weightfn )h->sh.weight[0][1].weightfn[8>>2]( h->mb.pic.p_fdec[1], FDEC_STRIDE,h->mb.pic.p_fdec[1], FDEC_STRIDE,&h->sh.weight[0][1], height );if( h->sh.weight[0][2].weightfn )h->sh.weight[0][2].weightfn[8>>2]( h->mb.pic.p_fdec[2], FDEC_STRIDE,h->mb.pic.p_fdec[2], FDEC_STRIDE,&h->sh.weight[0][2], height );}}x264_macroblock_encode_skip( h );    编码skip类型宏块return;}/*======== B-skip ========*/if( h->mb.i_type == B_SKIP ){/* don't do bskip motion compensation if it was already done in macroblock_analyse */if( !h->mb.b_skip_mc )x264_mb_mc( h );x264_macroblock_encode_skip( h );    编码skip类型宏块return;}/*======== 帧内 ========*/if( h->mb.i_type == I_16x16 ){h->mb.b_transform_8x8 = 0;for( int p = 0; p < plane_count; p++, i_qp = h->mb.i_chroma_qp )x264_mb_encode_i16x16( h, p, i_qp );   如果是Intra16x16类型，调用x264_mb_encode_i16x16()编码宏块(分别编码Y，U，V)}else if( h->mb.i_type == I_8x8 ){h->mb.b_transform_8x8 = 1;/* If we already encoded 3 of the 4 i8x8 blocks, we don't have to do them again. */if( h->mb.i_skip_intra ){h->mc.copy[PIXEL_16x16]( h->mb.pic.p_fdec[0], FDEC_STRIDE, h->mb.pic.i8x8_fdec_buf, 16, 16 );M32( &h->mb.cache.non_zero_count[x264_scan8[ 0]] ) = h->mb.pic.i8x8_nnz_buf[0];M32( &h->mb.cache.non_zero_count[x264_scan8[ 2]] ) = h->mb.pic.i8x8_nnz_buf[1];M32( &h->mb.cache.non_zero_count[x264_scan8[ 8]] ) = h->mb.pic.i8x8_nnz_buf[2];M32( &h->mb.cache.non_zero_count[x264_scan8[10]] ) = h->mb.pic.i8x8_nnz_buf[3];h->mb.i_cbp_luma = h->mb.pic.i8x8_cbp;/* In RD mode, restore the now-overwritten DCT data. */if( h->mb.i_skip_intra == 2 )h->mc.memcpy_aligned( h->dct.luma8x8, h->mb.pic.i8x8_dct_buf, sizeof(h->mb.pic.i8x8_dct_buf) );}for( int p = 0; p < plane_count; p++, i_qp = h->mb.i_chroma_qp ){for( int i = (p == 0 && h->mb.i_skip_intra) ? 3 : 0 ; i < 4; i++ ){int i_mode = h->mb.cache.intra4x4_pred_mode[x264_scan8[4*i]];x264_mb_encode_i8x8( h, p, i, i_qp, i_mode, NULL, 1 );  如果是Intra8x8类型，循环4次调用x264_mb_encode_i8x8()编码宏块}}}else if( h->mb.i_type == I_4x4 ){h->mb.b_transform_8x8 = 0;/* If we already encoded 15 of the 16 i4x4 blocks, we don't have to do them again. */if( h->mb.i_skip_intra ){h->mc.copy[PIXEL_16x16]( h->mb.pic.p_fdec[0], FDEC_STRIDE, h->mb.pic.i4x4_fdec_buf, 16, 16 );M32( &h->mb.cache.non_zero_count[x264_scan8[ 0]] ) = h->mb.pic.i4x4_nnz_buf[0];M32( &h->mb.cache.non_zero_count[x264_scan8[ 2]] ) = h->mb.pic.i4x4_nnz_buf[1];M32( &h->mb.cache.non_zero_count[x264_scan8[ 8]] ) = h->mb.pic.i4x4_nnz_buf[2];M32( &h->mb.cache.non_zero_count[x264_scan8[10]] ) = h->mb.pic.i4x4_nnz_buf[3];h->mb.i_cbp_luma = h->mb.pic.i4x4_cbp;/* In RD mode, restore the now-overwritten DCT data. */if( h->mb.i_skip_intra == 2 )h->mc.memcpy_aligned( h->dct.luma4x4, h->mb.pic.i4x4_dct_buf, sizeof(h->mb.pic.i4x4_dct_buf) );}for( int p = 0; p < plane_count; p++, i_qp = h->mb.i_chroma_qp ){for( int i = (p == 0 && h->mb.i_skip_intra) ? 15 : 0 ; i < 16; i++ ){pixel *p_dst = &h->mb.pic.p_fdec[p][block_idx_xy_fdec[i]];int i_mode = h->mb.cache.intra4x4_pred_mode[x264_scan8[i]];if( (h->mb.i_neighbour4[i] & (MB_TOPRIGHT|MB_TOP)) == MB_TOP )/* emulate missing topright samples */MPIXEL_X4( &p_dst[4-FDEC_STRIDE] ) = PIXEL_SPLAT_X4( p_dst[3-FDEC_STRIDE] );x264_mb_encode_i4x4( h, p, i, i_qp, i_mode, 1 ); 如果是Intra4x4类型，循环16次调用x264_mb_encode_i4x4()编码宏块}}}/*======== 帧间 ========*/else    /* Inter MB */{int i_decimate_mb = 0;/* Don't repeat motion compensation if it was already done in non-RD transform analysis */if( !h->mb.b_skip_mc )x264_mb_mc( h );if( h->mb.b_lossless )//===================lossless情况{if( h->mb.b_transform_8x8 )for( int p = 0; p < plane_count; p++ )for( int i8x8 = 0; i8x8 < 4; i8x8++ ){int x = i8x8&1;int y = i8x8>>1;nz = h->zigzagf.sub_8x8( h->dct.luma8x8[p*4+i8x8], h->mb.pic.p_fenc[p] + 8*x + 8*y*FENC_STRIDE,h->mb.pic.p_fdec[p] + 8*x + 8*y*FDEC_STRIDE );STORE_8x8_NNZ( p, i8x8, nz );h->mb.i_cbp_luma |= nz << i8x8;}elsefor( int p = 0; p < plane_count; p++ )for( int i4x4 = 0; i4x4 < 16; i4x4++ ){nz = h->zigzagf.sub_4x4( h->dct.luma4x4[p*16+i4x4],h->mb.pic.p_fenc[p]+block_idx_xy_fenc[i4x4],h->mb.pic.p_fdec[p]+block_idx_xy_fdec[i4x4] );h->mb.cache.non_zero_count[x264_scan8[p*16+i4x4]] = nz;h->mb.i_cbp_luma |= nz << (i4x4>>2);}}else if( h->mb.b_transform_8x8 )//===================DCT8x8情况{ALIGNED_ARRAY_N( dctcoef, dct8x8,[4],[64] );b_decimate &= !h->mb.b_trellis || !h->param.b_cabac; // 8x8 trellis is inherently optimal decimation for CABACfor( int p = 0; p < plane_count; p++, i_qp = h->mb.i_chroma_qp ){CLEAR_16x16_NNZ( p );h->dctf.sub16x16_dct8( dct8x8, h->mb.pic.p_fenc[p], h->mb.pic.p_fdec[p] );h->nr_count[1+!!p*2] += h->mb.b_noise_reduction * 4;int plane_cbp = 0;for( int idx = 0; idx < 4; idx++ ){nz = x264_quant_8x8( h, dct8x8[idx], i_qp, ctx_cat_plane[DCT_LUMA_8x8][p], 0, p, idx );if( nz ){h->zigzagf.scan_8x8( h->dct.luma8x8[p*4+idx], dct8x8[idx] );if( b_decimate ){int i_decimate_8x8 = h->quantf.decimate_score64( h->dct.luma8x8[p*4+idx] );i_decimate_mb += i_decimate_8x8;if( i_decimate_8x8 >= 4 )plane_cbp |= 1<<idx;}elseplane_cbp |= 1<<idx;}}if( i_decimate_mb >= 6 || !b_decimate ){h->mb.i_cbp_luma |= plane_cbp;FOREACH_BIT( idx, 0, plane_cbp ){h->quantf.dequant_8x8( dct8x8[idx], h->dequant8_mf[p?CQM_8PC:CQM_8PY], i_qp );h->dctf.add8x8_idct8( &h->mb.pic.p_fdec[p][8*(idx&1) + 8*(idx>>1)*FDEC_STRIDE], dct8x8[idx] );STORE_8x8_NNZ( p, idx, 1 );}}}}else//===================最普通的情况{// 帧间预测：16x16 宏块被划分为8x8,每个8x8再次被划分为4x4ALIGNED_ARRAY_N( dctcoef, dct4x4,[16],[16] );for( int p = 0; p < plane_count; p++, i_qp = h->mb.i_chroma_qp ){CLEAR_16x16_NNZ( p );//16x16DCT（实际上分解为16个4x4DCT）  //求编码帧p_fenc和重建帧p_fdec之间的残差，然后进行DCT变换h->dctf.sub16x16_dct( dct4x4, h->mb.pic.p_fenc[p], h->mb.pic.p_fdec[p] );   ///对16x16块调用x264_dct_function_t的sub16x16_dct()汇编函数，求得编码宏块数据p_fenc与重建宏块数据p_fdec之间的残差（“sub”），并对残差进行DCT变换if( h->mb.b_noise_reduction ){h->nr_count[0+!!p*2] += 16;for( int idx = 0; idx < 16; idx++ )h->quantf.denoise_dct( dct4x4[idx], h->nr_residual_sum[0+!!p*2], h->nr_offset[0+!!p*2], 16 );}int plane_cbp = 0;//16x16的块分成4个8x8的块for( int i8x8 = 0; i8x8 < 4; i8x8++ ){int i_decimate_8x8 = b_decimate ? 0 : 6;int nnz8x8 = 0;if( h->mb.b_trellis ){for( int i4x4 = 0; i4x4 < 4; i4x4++ ){int idx = i8x8*4+i4x4;if( x264_quant_4x4_trellis( h, dct4x4[idx], CQM_4PY, i_qp, ctx_cat_plane[DCT_LUMA_4x4][p], 0, !!p, p*16+idx ) ){h->zigzagf.scan_4x4( h->dct.luma4x4[p*16+idx], dct4x4[idx] );h->quantf.dequant_4x4( dct4x4[idx], h->dequant4_mf[p?CQM_4PC:CQM_4PY], i_qp );if( i_decimate_8x8 < 6 )i_decimate_8x8 += h->quantf.decimate_score16( h->dct.luma4x4[p*16+idx] );h->mb.cache.non_zero_count[x264_scan8[p*16+idx]] = 1;nnz8x8 = 1;}}}else{//8x8的块分成4个4x4的块，每个4x4的块再分别进行量化nnz8x8 = nz = h->quantf.quant_4x4x4( &dct4x4[i8x8*4], h->quant4_mf[CQM_4PY][i_qp], h->quant4_bias[CQM_4PY][i_qp] );   /分成4个8x8的块，对每个8x8块分别调用x264_quant_function_t的quant_4x4x4()汇编函数进行量化if( nz ){FOREACH_BIT( idx, i8x8*4, nz ){h->zigzagf.scan_4x4( h->dct.luma4x4[p*16+idx], dct4x4[idx] );//建立重建帧h->quantf.dequant_4x4( dct4x4[idx], h->dequant4_mf[p?CQM_4PC:CQM_4PY], i_qp ); //分成16个4x4的块，对每个4x4块分别调用x264_quant_function_t的dequant_4x4()汇编函数进行反量化（用于重建帧）if( i_decimate_8x8 < 6 )i_decimate_8x8 += h->quantf.decimate_score16( h->dct.luma4x4[p*16+idx] );h->mb.cache.non_zero_count[x264_scan8[p*16+idx]] = 1;}}}if( nnz8x8 ){i_decimate_mb += i_decimate_8x8;if( i_decimate_8x8 < 4 )STORE_8x8_NNZ( p, i8x8, 0 );elseplane_cbp |= 1<<i8x8;}}if( i_decimate_mb < 6 ){plane_cbp = 0;CLEAR_16x16_NNZ( p );}else{h->mb.i_cbp_luma |= plane_cbp;FOREACH_BIT( i8x8, 0, plane_cbp ){//用于建立重建帧  //残差进行DCT反变换之后，叠加到预测数据上h->dctf.add8x8_idct( &h->mb.pic.p_fdec[p][(i8x8&1)*8 + (i8x8>>1)*8*FDEC_STRIDE], &dct4x4[i8x8*4] );    分成4个8x8的块，对每个8x8块分别调用x264_dct_function_t的add8x8_idct()汇编函数，对残差进行DCT反变换，并将反变换后的数据叠加（“add”）至预测数据上（用于重建帧）}}}}}/* encode chroma */if( chroma ){if( IS_INTRA( h->mb.i_type ) ){int i_mode = h->mb.i_chroma_pred_mode;if( h->mb.b_lossless )x264_predict_lossless_chroma( h, i_mode );else{h->predict_chroma[i_mode]( h->mb.pic.p_fdec[1] );h->predict_chroma[i_mode]( h->mb.pic.p_fdec[2] );}}/* encode the 8x8 blocks */x264_mb_encode_chroma( h, !IS_INTRA( h->mb.i_type ), h->mb.i_chroma_qp );  /编码色度块}elseh->mb.i_cbp_chroma = 0;/* store cbp */int cbp = h->mb.i_cbp_chroma << 4 | h->mb.i_cbp_luma;if( h->param.b_cabac )cbp |= h->mb.cache.non_zero_count[x264_scan8[LUMA_DC    ]] << 8|  h->mb.cache.non_zero_count[x264_scan8[CHROMA_DC+0]] << 9|  h->mb.cache.non_zero_count[x264_scan8[CHROMA_DC+1]] << 10;h->mb.cbp[h->mb.i_mb_xy] = cbp;/* Check for P_SKIP* XXX: in the me perhaps we should take x264_mb_predict_mv_pskip into account*      (if multiple mv give same result)*/if( !b_force_no_skip ){if( h->mb.i_type == P_L0 && h->mb.i_partition == D_16x16 &&!(h->mb.i_cbp_luma | h->mb.i_cbp_chroma) &&M32( h->mb.cache.mv[0][x264_scan8[0]] ) == M32( h->mb.cache.pskip_mv )&& h->mb.cache.ref[0][x264_scan8[0]] == 0 ){h->mb.i_type = P_SKIP;}/* Check for B_SKIP */if( h->mb.i_type == B_DIRECT && !(h->mb.i_cbp_luma | h->mb.i_cbp_chroma) ){h->mb.i_type = B_SKIP;}}
}

从源代码可以看出，x264_macroblock_encode_internal()的流程大致如下：

（1）、如果是Skip类型，调用x264_macroblock_encode_skip()编码宏块。

（2）、如果是Intra16x16类型，调用x264_mb_encode_i16x16()编码宏块。

（3）、如果是Intra4x4类型，循环16次调用x264_mb_encode_i4x4()编码宏块。

（4）、如果是Inter类型，则不再调用子函数，而是直接进行编码：

a)、对16x16块调用x264_dct_function_t的sub16x16_dct()汇编函数，求得编码宏块数据p_fenc与重建宏块数据p_fdec之间的残差（“sub”），并对残差进行DCT变换。

b)、分成4个8x8的块，对每个8x8块分别调用x264_quant_function_t的quant_4x4x4()汇编函数进行量化。

c)、分成16个4x4的块，对每个4x4块分别调用x264_quant_function_t的dequant_4x4()汇编函数进行反量化（用于重建帧）。

d)、分成4个8x8的块，对每个8x8块分别调用x264_dct_function_t的add8x8_idct()汇编函数，对残差进行DCT反变换，并将反变换后的数据叠加（“add”）至预测数据上（用于重建帧）。

（5）、如果对色度编码，调用x264_mb_encode_chroma()。

从Inter宏块编码的步骤可以看出，编码就是“DCT变换+量化”两步的组合。在接下来的文章中将依次分析变换、量化的具体代码。