x264代码剖析（六）：encode()函数之x264_encoder_headers()函数

x264代码剖析（六）：encode()函数之x264_encoder_headers()函数

 

        encode()函数是x264的主干函数，主要包括x264_encoder_open()函数、x264_encoder_headers()函数、x264_encoder_encode()函数与x264_encoder_close()函数四大部分，其中x264_encoder_encode()函数是其核心部分，具体的H.264视频编码算法均在此模块。上一篇博文主要分析了x264_encoder_open()函数，本文主要学习x264_encoder_headers()函数。

 

        x264_encoder_headers()是libx264的一个API函数，用于输出SPS/PPS/SEI这些H.264码流的头信息，如下图所示。它调用了下面的函数：

x264_sps_write()：输出SPS

x264_pps_write()：输出PPS

x264_sei_version_write()：输出SEI

 

        下面对x264_encoder_headers()函数所涉及的函数进行介绍，首先就是SPS与PPS的初始化工作；其次是x264_encoder_headers()函数的内容；最后就是x264_encoder_headers()函数中用于输出SPS/PPS/SEI这些H.264码流头信息的具体函数，即x264_sps_write()函数、x264_pps_write()函数与x264_sei_version_write()函数。

 

1、SPS与PPS的初始化函数x264_sps_init()、x264_pps_init()

 

        x264_sps_init()根据输入参数生成H.264码流的SPS（Sequence Parameter Set，序列参数集）信息，即根据输入参数集x264_param_t中的信息，初始化了SPS结构体中的成员变量。该函数的定义位于encoder\set.c，对应的代码如下：

 

////////////////初始化SPS
void x264_sps_init( x264_sps_t *sps, int i_id, x264_param_t *param )
{
    int csp = param->i_csp & X264_CSP_MASK;

    sps->i_id = i_id;
    sps->i_mb_width = ( param->i_width + 15 ) / 16;	//以宏块为单位的宽度
    sps->i_mb_height= ( param->i_height + 15 ) / 16;	//以宏块为单位的高度
    sps->i_chroma_format_idc = csp >= X264_CSP_I444 ? CHROMA_444 :
                               csp >= X264_CSP_I422 ? CHROMA_422 : CHROMA_420;	//色度取样格式

    sps->b_qpprime_y_zero_transform_bypass = param->rc.i_rc_method == X264_RC_CQP && param->rc.i_qp_constant == 0;
    //型profile
	if( sps->b_qpprime_y_zero_transform_bypass || sps->i_chroma_format_idc == CHROMA_444 )
        sps->i_profile_idc  = PROFILE_HIGH444_PREDICTIVE;	//YUV444的时候
    else if( sps->i_chroma_format_idc == CHROMA_422 )
        sps->i_profile_idc  = PROFILE_HIGH422;
    else if( BIT_DEPTH > 8 )
        sps->i_profile_idc  = PROFILE_HIGH10;
    else if( param->analyse.b_transform_8x8 || param->i_cqm_preset != X264_CQM_FLAT )
        sps->i_profile_idc  = PROFILE_HIGH;	//高型 High Profile 目前最常见
    else if( param->b_cabac || param->i_bframe > 0 || param->b_interlaced || param->b_fake_interlaced || param->analyse.i_weighted_pred > 0 )
        sps->i_profile_idc  = PROFILE_MAIN;	//主型 
    else
        sps->i_profile_idc  = PROFILE_BASELINE;	//基本型

    sps->b_constraint_set0  = sps->i_profile_idc == PROFILE_BASELINE;
    /* x264 doesn't support the features that are in Baseline and not in Main,
     * namely arbitrary_slice_order and slice_groups. */
    sps->b_constraint_set1  = sps->i_profile_idc <= PROFILE_MAIN;
    /* Never set constraint_set2, it is not necessary and not used in real world. */
    sps->b_constraint_set2  = 0;
    sps->b_constraint_set3  = 0;

	//级level
    sps->i_level_idc = param->i_level_idc;
    if( param->i_level_idc == 9 && ( sps->i_profile_idc == PROFILE_BASELINE || sps->i_profile_idc == PROFILE_MAIN ) )
    {
        sps->b_constraint_set3 = 1; /* level 1b with Baseline or Main profile is signalled via constraint_set3 */
        sps->i_level_idc      = 11;
    }
    /* Intra profiles */
    if( param->i_keyint_max == 1 && sps->i_profile_idc > PROFILE_HIGH )
        sps->b_constraint_set3 = 1;

    sps->vui.i_num_reorder_frames = param->i_bframe_pyramid ? 2 : param->i_bframe ? 1 : 0;
    /* extra slot with pyramid so that we don't have to override the
     * order of forgetting old pictures */
	//参考帧数量
    sps->vui.i_max_dec_frame_buffering =
    sps->i_num_ref_frames = X264_MIN(X264_REF_MAX, X264_MAX4(param->i_frame_reference, 1 + sps->vui.i_num_reorder_frames,
                            param->i_bframe_pyramid ? 4 : 1, param->i_dpb_size));
    sps->i_num_ref_frames -= param->i_bframe_pyramid == X264_B_PYRAMID_STRICT;
    if( param->i_keyint_max == 1 )
    {
        sps->i_num_ref_frames = 0;
        sps->vui.i_max_dec_frame_buffering = 0;
    }

    /* number of refs + current frame */
    int max_frame_num = sps->vui.i_max_dec_frame_buffering * (!!param->i_bframe_pyramid+1) + 1;
    /* Intra refresh cannot write a recovery time greater than max frame num-1 */
    if( param->b_intra_refresh )
    {
        int time_to_recovery = X264_MIN( sps->i_mb_width - 1, param->i_keyint_max ) + param->i_bframe - 1;
        max_frame_num = X264_MAX( max_frame_num, time_to_recovery+1 );
    }

    sps->i_log2_max_frame_num = 4;
    while( (1 << sps->i_log2_max_frame_num) <= max_frame_num )
        sps->i_log2_max_frame_num++;
	
	//POC类型
    sps->i_poc_type = param->i_bframe || param->b_interlaced || param->i_avcintra_class ? 0 : 2;
    if( sps->i_poc_type == 0 )
    {
        int max_delta_poc = (param->i_bframe + 2) * (!!param->i_bframe_pyramid + 1) * 2;
        sps->i_log2_max_poc_lsb = 4;
        while( (1 << sps->i_log2_max_poc_lsb) <= max_delta_poc * 2 )
            sps->i_log2_max_poc_lsb++;
    }

    sps->b_vui = 1;

    sps->b_gaps_in_frame_num_value_allowed = 0;
    sps->b_frame_mbs_only = !(param->b_interlaced || param->b_fake_interlaced);
    if( !sps->b_frame_mbs_only )
        sps->i_mb_height = ( sps->i_mb_height + 1 ) & ~1;
    sps->b_mb_adaptive_frame_field = param->b_interlaced;
    sps->b_direct8x8_inference = 1;

    sps->crop.i_left   = param->crop_rect.i_left;
    sps->crop.i_top    = param->crop_rect.i_top;
    sps->crop.i_right  = param->crop_rect.i_right + sps->i_mb_width*16 - param->i_width;
    sps->crop.i_bottom = (param->crop_rect.i_bottom + sps->i_mb_height*16 - param->i_height) >> !sps->b_frame_mbs_only;
    sps->b_crop = sps->crop.i_left  || sps->crop.i_top ||
                  sps->crop.i_right || sps->crop.i_bottom;

    sps->vui.b_aspect_ratio_info_present = 0;
    if( param->vui.i_sar_width > 0 && param->vui.i_sar_height > 0 )
    {
        sps->vui.b_aspect_ratio_info_present = 1;
        sps->vui.i_sar_width = param->vui.i_sar_width;
        sps->vui.i_sar_height= param->vui.i_sar_height;
    }

    sps->vui.b_overscan_info_present = param->vui.i_overscan > 0 && param->vui.i_overscan <= 2;
    if( sps->vui.b_overscan_info_present )
        sps->vui.b_overscan_info = ( param->vui.i_overscan == 2 ? 1 : 0 );

    sps->vui.b_signal_type_present = 0;
    sps->vui.i_vidformat = ( param->vui.i_vidformat >= 0 && param->vui.i_vidformat <= 5 ? param->vui.i_vidformat : 5 );
    sps->vui.b_fullrange = ( param->vui.b_fullrange >= 0 && param->vui.b_fullrange <= 1 ? param->vui.b_fullrange :
                           ( csp >= X264_CSP_BGR ? 1 : 0 ) );
    sps->vui.b_color_description_present = 0;

    sps->vui.i_colorprim = ( param->vui.i_colorprim >= 0 && param->vui.i_colorprim <=  9 ? param->vui.i_colorprim : 2 );
    sps->vui.i_transfer  = ( param->vui.i_transfer  >= 0 && param->vui.i_transfer  <= 15 ? param->vui.i_transfer  : 2 );
    sps->vui.i_colmatrix = ( param->vui.i_colmatrix >= 0 && param->vui.i_colmatrix <= 10 ? param->vui.i_colmatrix :
                           ( csp >= X264_CSP_BGR ? 0 : 2 ) );
    if( sps->vui.i_colorprim != 2 ||
        sps->vui.i_transfer  != 2 ||
        sps->vui.i_colmatrix != 2 )
    {
        sps->vui.b_color_description_present = 1;
    }

    if( sps->vui.i_vidformat != 5 ||
        sps->vui.b_fullrange ||
        sps->vui.b_color_description_present )
    {
        sps->vui.b_signal_type_present = 1;
    }

    /* FIXME: not sufficient for interlaced video */
    sps->vui.b_chroma_loc_info_present = param->vui.i_chroma_loc > 0 && param->vui.i_chroma_loc <= 5 &&
                                         sps->i_chroma_format_idc == CHROMA_420;
    if( sps->vui.b_chroma_loc_info_present )
    {
        sps->vui.i_chroma_loc_top = param->vui.i_chroma_loc;
        sps->vui.i_chroma_loc_bottom = param->vui.i_chroma_loc;
    }

    sps->vui.b_timing_info_present = param->i_timebase_num > 0 && param->i_timebase_den > 0;

    if( sps->vui.b_timing_info_present )
    {
        sps->vui.i_num_units_in_tick = param->i_timebase_num;
        sps->vui.i_time_scale = param->i_timebase_den * 2;
        sps->vui.b_fixed_frame_rate = !param->b_vfr_input;
    }

    sps->vui.b_vcl_hrd_parameters_present = 0; // we don't support VCL HRD
    sps->vui.b_nal_hrd_parameters_present = !!param->i_nal_hrd;
    sps->vui.b_pic_struct_present = param->b_pic_struct;

    // NOTE: HRD related parts of the SPS are initialised in x264_ratecontrol_init_reconfigurable

    sps->vui.b_bitstream_restriction = param->i_keyint_max > 1;
    if( sps->vui.b_bitstream_restriction )
    {
        sps->vui.b_motion_vectors_over_pic_boundaries = 1;
        sps->vui.i_max_bytes_per_pic_denom = 0;
        sps->vui.i_max_bits_per_mb_denom = 0;
        sps->vui.i_log2_max_mv_length_horizontal =
        sps->vui.i_log2_max_mv_length_vertical = (int)log2f( X264_MAX( 1, param->analyse.i_mv_range*4-1 ) ) + 1;
    }
}

        x264_pps_init()根据输入参数生成H.264码流的PPS（Picture Parameter Set，图像参数集）信息，即根据输入参数集x264_param_t中的信息，初始化了PPS结构体中的成员变量。该函数的定义位于encoder\set.c，对应的代码如下：

 

////////////////初始化PPS
void x264_pps_init( x264_pps_t *pps, int i_id, x264_param_t *param, x264_sps_t *sps )
{
    pps->i_id = i_id;
    pps->i_sps_id = sps->i_id;	//所属的SPS
    pps->b_cabac = param->b_cabac;	//是否使用CABAC？


    pps->b_pic_order = !param->i_avcintra_class && param->b_interlaced;
    pps->i_num_slice_groups = 1;


	//目前参考帧队列的长度  
    //注意是这个队列中当前实际的、已存在的参考帧数目，这从它的名字“active”中也可以看出来。
    pps->i_num_ref_idx_l0_default_active = param->i_frame_reference;
    pps->i_num_ref_idx_l1_default_active = 1;


	//加权预测
    pps->b_weighted_pred = param->analyse.i_weighted_pred > 0;
    pps->b_weighted_bipred = param->analyse.b_weighted_bipred ? 2 : 0;


	//量化参数QP的初始值
    pps->i_pic_init_qp = param->rc.i_rc_method == X264_RC_ABR || param->b_stitchable ? 26 + QP_BD_OFFSET : SPEC_QP( param->rc.i_qp_constant );
    pps->i_pic_init_qs = 26 + QP_BD_OFFSET;


    pps->i_chroma_qp_index_offset = param->analyse.i_chroma_qp_offset;
    pps->b_deblocking_filter_control = 1;
    pps->b_constrained_intra_pred = param->b_constrained_intra;
    pps->b_redundant_pic_cnt = 0;


    pps->b_transform_8x8_mode = param->analyse.b_transform_8x8 ? 1 : 0;


    pps->i_cqm_preset = param->i_cqm_preset;


    switch( pps->i_cqm_preset )
    {
    case X264_CQM_FLAT:
        for( int i = 0; i < 8; i++ )
            pps->scaling_list[i] = x264_cqm_flat16;
        break;
    case X264_CQM_JVT:
        for( int i = 0; i < 8; i++ )
            pps->scaling_list[i] = x264_cqm_jvt[i];
        break;
    case X264_CQM_CUSTOM:
        /* match the transposed DCT & zigzag */
        transpose( param->cqm_4iy, 4 );
        transpose( param->cqm_4py, 4 );
        transpose( param->cqm_4ic, 4 );
        transpose( param->cqm_4pc, 4 );
        transpose( param->cqm_8iy, 8 );
        transpose( param->cqm_8py, 8 );
        transpose( param->cqm_8ic, 8 );
        transpose( param->cqm_8pc, 8 );
        pps->scaling_list[CQM_4IY] = param->cqm_4iy;
        pps->scaling_list[CQM_4PY] = param->cqm_4py;
        pps->scaling_list[CQM_4IC] = param->cqm_4ic;
        pps->scaling_list[CQM_4PC] = param->cqm_4pc;
        pps->scaling_list[CQM_8IY+4] = param->cqm_8iy;
        pps->scaling_list[CQM_8PY+4] = param->cqm_8py;
        pps->scaling_list[CQM_8IC+4] = param->cqm_8ic;
        pps->scaling_list[CQM_8PC+4] = param->cqm_8pc;
        for( int i = 0; i < 8; i++ )
            for( int j = 0; j < (i < 4 ? 16 : 64); j++ )
                if( pps->scaling_list[i][j] == 0 )
                    pps->scaling_list[i] = x264_cqm_jvt[i];
        break;
    }
}

2、x264_encoder_headers()函数

 

        x264_encoder_headers()是libx264的一个API函数，用于输出SPS/PPS/SEI这些H.264码流的头信息，x264_encoder_headers()的定义位于encoder\encoder.c。x264_encoder_headers()分别调用了x264_sps_write()，x264_pps_write()，x264_sei_version_write()输出了SPS，PPS，和SEI信息。在输出每个NALU之前，需要调用x264_nal_start()，在输出NALU之后，需要调用x264_nal_end()。对应的代码分析如下：

 

/******************************************************************/
/******************************************************************/
/*
======Analysed by RuiDong Fang
======Csdn Blog:http://blog.csdn.net/frd2009041510
======Date:2016.03.09
 */
/******************************************************************/
/******************************************************************/

/************====== x264_encoder_headers()函数 ======************/
/*
功能：x264_encoder_headers()是libx264的一个API函数，用于输出SPS/PPS/SEI这些H.264码流的头信息
*/
/****************************************************************************
 * x264_encoder_headers:
 ****************************************************************************/
int x264_encoder_headers( x264_t *h, x264_nal_t **pp_nal, int *pi_nal )
{
    int frame_size = 0;
    /* init bitstream context */
    h->out.i_nal = 0;
    bs_init( &h->out.bs, h->out.p_bitstream, h->out.i_bitstream );

    /* Write SEI, SPS and PPS. */
	/*在输出每个NALU之前，需要调用x264_nal_start()，在输出NALU之后，需要调用x264_nal_end()*/
    /* generate sequence parameters */
    x264_nal_start( h, NAL_SPS, NAL_PRIORITY_HIGHEST );
    x264_sps_write( &h->out.bs, h->sps );	//////////////////////////输出SPS
    if( x264_nal_end( h ) )
        return -1;

    /* generate picture parameters */
    x264_nal_start( h, NAL_PPS, NAL_PRIORITY_HIGHEST );
    x264_pps_write( &h->out.bs, h->sps, h->pps );	//////////////////////////输出PPS
    if( x264_nal_end( h ) )
        return -1;

    /* identify ourselves */
    x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );
    if( x264_sei_version_write( h, &h->out.bs ) )	//////////////////////////输出SEI（其中包含了配置信息）
        return -1;
    if( x264_nal_end( h ) )
        return -1;

    frame_size = x264_encoder_encapsulate_nals( h, 0 );
    if( frame_size < 0 )
        return -1;

    /* now set output*/
    *pi_nal = h->out.i_nal;
    *pp_nal = &h->out.nal[0];
    h->out.i_nal = 0;

    return frame_size;
}

2.1、x264_sps_write()函数

 

        x264_sps_write()用于输出SPS。该函数的定义位于encoder\set.c，x264_sps_write()将x264_sps_t结构体中的信息输出出来形成了一个NALU。对应的代码如下：

 

////////////////输出SPS
void x264_sps_write( bs_t *s, x264_sps_t *sps )
{
    bs_realign( s );
    bs_write( s, 8, sps->i_profile_idc );	//型profile，8bit
    bs_write1( s, sps->b_constraint_set0 );
    bs_write1( s, sps->b_constraint_set1 );
    bs_write1( s, sps->b_constraint_set2 );
    bs_write1( s, sps->b_constraint_set3 );

    bs_write( s, 4, 0 );    /* reserved */

    bs_write( s, 8, sps->i_level_idc );	//级level，8bit

    bs_write_ue( s, sps->i_id );	//本SPS的 id号

    if( sps->i_profile_idc >= PROFILE_HIGH )
    {
        //色度取样格式  
        //0代表单色  
        //1代表4:2:0  
        //2代表4:2:2  
        //3代表4:4:4
		bs_write_ue( s, sps->i_chroma_format_idc );
        if( sps->i_chroma_format_idc == CHROMA_444 )
            bs_write1( s, 0 ); // separate_colour_plane_flag
		//亮度  
        //颜色位深=bit_depth_luma_minus8+8
        bs_write_ue( s, BIT_DEPTH-8 ); // bit_depth_luma_minus8
		//色度与亮度一样
        bs_write_ue( s, BIT_DEPTH-8 ); // bit_depth_chroma_minus8
        bs_write1( s, sps->b_qpprime_y_zero_transform_bypass );
        bs_write1( s, 0 ); // seq_scaling_matrix_present_flag
    }

	//log2_max_frame_num_minus4主要是为读取另一个句法元素frame_num服务的  
    //frame_num 是最重要的句法元素之一  
    //这个句法元素指明了frame_num的所能达到的最大值：  
    //MaxFrameNum = 2^( log2_max_frame_num_minus4 + 4 )
    bs_write_ue( s, sps->i_log2_max_frame_num - 4 );

	//pic_order_cnt_type 指明了poc (picture order count) 的编码方法  
    //poc标识图像的播放顺序。  
    //由于H.264使用了B帧预测，使得图像的解码顺序并不一定等于播放顺序，但它们之间存在一定的映射关系  
    //poc 可以由frame-num 通过映射关系计算得来，也可以索性由编码器显式地传送。  
    //H.264 中一共定义了三种poc 的编码方法
    bs_write_ue( s, sps->i_poc_type );
    if( sps->i_poc_type == 0 )
        bs_write_ue( s, sps->i_log2_max_poc_lsb - 4 );

	//num_ref_frames 指定参考帧队列可能达到的最大长度，解码器依照这个句法元素的值开辟存储区，这个存储区用于存放已解码的参考帧，  
    //H.264 规定最多可用16 个参考帧，因此最大值为16。
    bs_write_ue( s, sps->i_num_ref_frames );
    bs_write1( s, sps->b_gaps_in_frame_num_value_allowed );

	//pic_width_in_mbs_minus1加1后为图像宽（以宏块为单位）：  
    //           PicWidthInMbs = pic_width_in_mbs_minus1 + 1  
    //以像素为单位图像宽度（亮度）：width=PicWidthInMbs*16
    bs_write_ue( s, sps->i_mb_width - 1 );

	//pic_height_in_map_units_minus1加1后指明图像高度（以宏块为单位）
    bs_write_ue( s, (sps->i_mb_height >> !sps->b_frame_mbs_only) - 1);
    bs_write1( s, sps->b_frame_mbs_only );
    if( !sps->b_frame_mbs_only )
        bs_write1( s, sps->b_mb_adaptive_frame_field );
    bs_write1( s, sps->b_direct8x8_inference );

    bs_write1( s, sps->b_crop );
    if( sps->b_crop )
    {
        int h_shift = sps->i_chroma_format_idc == CHROMA_420 || sps->i_chroma_format_idc == CHROMA_422;
        int v_shift = sps->i_chroma_format_idc == CHROMA_420;
        bs_write_ue( s, sps->crop.i_left   >> h_shift );
        bs_write_ue( s, sps->crop.i_right  >> h_shift );
        bs_write_ue( s, sps->crop.i_top    >> v_shift );
        bs_write_ue( s, sps->crop.i_bottom >> v_shift );
    }

    bs_write1( s, sps->b_vui );
    if( sps->b_vui )
    {
        bs_write1( s, sps->vui.b_aspect_ratio_info_present );
        if( sps->vui.b_aspect_ratio_info_present )
        {
            int i;
            static const struct { uint8_t w, h, sar; } sar[] =
            {
                // aspect_ratio_idc = 0 -> unspecified
                {  1,  1, 1 }, { 12, 11, 2 }, { 10, 11, 3 }, { 16, 11, 4 },
                { 40, 33, 5 }, { 24, 11, 6 }, { 20, 11, 7 }, { 32, 11, 8 },
                { 80, 33, 9 }, { 18, 11, 10}, { 15, 11, 11}, { 64, 33, 12},
                {160, 99, 13}, {  4,  3, 14}, {  3,  2, 15}, {  2,  1, 16},
                // aspect_ratio_idc = [17..254] -> reserved
                { 0, 0, 255 }
            };
            for( i = 0; sar[i].sar != 255; i++ )
            {
                if( sar[i].w == sps->vui.i_sar_width &&
                    sar[i].h == sps->vui.i_sar_height )
                    break;
            }
            bs_write( s, 8, sar[i].sar );
            if( sar[i].sar == 255 ) /* aspect_ratio_idc (extended) */
            {
                bs_write( s, 16, sps->vui.i_sar_width );
                bs_write( s, 16, sps->vui.i_sar_height );
            }
        }

        bs_write1( s, sps->vui.b_overscan_info_present );
        if( sps->vui.b_overscan_info_present )
            bs_write1( s, sps->vui.b_overscan_info );

        bs_write1( s, sps->vui.b_signal_type_present );
        if( sps->vui.b_signal_type_present )
        {
            bs_write( s, 3, sps->vui.i_vidformat );
            bs_write1( s, sps->vui.b_fullrange );
            bs_write1( s, sps->vui.b_color_description_present );
            if( sps->vui.b_color_description_present )
            {
                bs_write( s, 8, sps->vui.i_colorprim );
                bs_write( s, 8, sps->vui.i_transfer );
                bs_write( s, 8, sps->vui.i_colmatrix );
            }
        }

        bs_write1( s, sps->vui.b_chroma_loc_info_present );
        if( sps->vui.b_chroma_loc_info_present )
        {
            bs_write_ue( s, sps->vui.i_chroma_loc_top );
            bs_write_ue( s, sps->vui.i_chroma_loc_bottom );
        }

        bs_write1( s, sps->vui.b_timing_info_present );
        if( sps->vui.b_timing_info_present )
        {
            bs_write32( s, sps->vui.i_num_units_in_tick );
            bs_write32( s, sps->vui.i_time_scale );
            bs_write1( s, sps->vui.b_fixed_frame_rate );
        }

        bs_write1( s, sps->vui.b_nal_hrd_parameters_present );
        if( sps->vui.b_nal_hrd_parameters_present )
        {
            bs_write_ue( s, sps->vui.hrd.i_cpb_cnt - 1 );
            bs_write( s, 4, sps->vui.hrd.i_bit_rate_scale );
            bs_write( s, 4, sps->vui.hrd.i_cpb_size_scale );

            bs_write_ue( s, sps->vui.hrd.i_bit_rate_value - 1 );
            bs_write_ue( s, sps->vui.hrd.i_cpb_size_value - 1 );

            bs_write1( s, sps->vui.hrd.b_cbr_hrd );

            bs_write( s, 5, sps->vui.hrd.i_initial_cpb_removal_delay_length - 1 );
            bs_write( s, 5, sps->vui.hrd.i_cpb_removal_delay_length - 1 );
            bs_write( s, 5, sps->vui.hrd.i_dpb_output_delay_length - 1 );
            bs_write( s, 5, sps->vui.hrd.i_time_offset_length );
        }

        bs_write1( s, sps->vui.b_vcl_hrd_parameters_present );

        if( sps->vui.b_nal_hrd_parameters_present || sps->vui.b_vcl_hrd_parameters_present )
            bs_write1( s, 0 );   /* low_delay_hrd_flag */

        bs_write1( s, sps->vui.b_pic_struct_present );
        bs_write1( s, sps->vui.b_bitstream_restriction );
        if( sps->vui.b_bitstream_restriction )
        {
            bs_write1( s, sps->vui.b_motion_vectors_over_pic_boundaries );
            bs_write_ue( s, sps->vui.i_max_bytes_per_pic_denom );
            bs_write_ue( s, sps->vui.i_max_bits_per_mb_denom );
            bs_write_ue( s, sps->vui.i_log2_max_mv_length_horizontal );
            bs_write_ue( s, sps->vui.i_log2_max_mv_length_vertical );
            bs_write_ue( s, sps->vui.i_num_reorder_frames );
            bs_write_ue( s, sps->vui.i_max_dec_frame_buffering );
        }
    }

	//RBSP拖尾  
    //无论比特流当前位置是否字节对齐 ， 都向其中写入一个比特1及若干个（0~7个）比特0 ， 使其字节对齐
    bs_rbsp_trailing( s );
    bs_flush( s );
}

2.2、x264_pps_write()函数

 

        x264_pps_write()用于输出PPS。该函数的定义位于encoder\set.c，x264_pps_write()将x264_pps_t结构体中的信息输出出来形成了一个NALU。对应的代码如下：

 

////////////////输出PPS
void x264_pps_write( bs_t *s, x264_sps_t *sps, x264_pps_t *pps )
{
    bs_realign( s );
    bs_write_ue( s, pps->i_id );	//PPS的ID
    bs_write_ue( s, pps->i_sps_id );//该PPS引用的SPS的ID

	//entropy_coding_mode_flag  
    //0表示熵编码使用CAVLC，1表示熵编码使用CABAC
    bs_write1( s, pps->b_cabac );
    bs_write1( s, pps->b_pic_order );
    bs_write_ue( s, pps->i_num_slice_groups - 1 );

    bs_write_ue( s, pps->i_num_ref_idx_l0_default_active - 1 );
    bs_write_ue( s, pps->i_num_ref_idx_l1_default_active - 1 );

	//P Slice 是否使用加权预测？
    bs_write1( s, pps->b_weighted_pred );
	//B Slice 是否使用加权预测？
    bs_write( s, 2, pps->b_weighted_bipred );

	//pic_init_qp_minus26加26后用以指明亮度分量的QP的初始值。
    bs_write_se( s, pps->i_pic_init_qp - 26 - QP_BD_OFFSET );
    bs_write_se( s, pps->i_pic_init_qs - 26 - QP_BD_OFFSET );
    bs_write_se( s, pps->i_chroma_qp_index_offset );

    bs_write1( s, pps->b_deblocking_filter_control );
    bs_write1( s, pps->b_constrained_intra_pred );
    bs_write1( s, pps->b_redundant_pic_cnt );

    if( pps->b_transform_8x8_mode || pps->i_cqm_preset != X264_CQM_FLAT )
    {
        bs_write1( s, pps->b_transform_8x8_mode );
        bs_write1( s, (pps->i_cqm_preset != X264_CQM_FLAT) );
        if( pps->i_cqm_preset != X264_CQM_FLAT )
        {
            scaling_list_write( s, pps, CQM_4IY );
            scaling_list_write( s, pps, CQM_4IC );
            bs_write1( s, 0 ); // Cr = Cb
            scaling_list_write( s, pps, CQM_4PY );
            scaling_list_write( s, pps, CQM_4PC );
            bs_write1( s, 0 ); // Cr = Cb
            if( pps->b_transform_8x8_mode )
            {
                if( sps->i_chroma_format_idc == CHROMA_444 )
                {
                    scaling_list_write( s, pps, CQM_8IY+4 );
                    scaling_list_write( s, pps, CQM_8IC+4 );
                    bs_write1( s, 0 ); // Cr = Cb
                    scaling_list_write( s, pps, CQM_8PY+4 );
                    scaling_list_write( s, pps, CQM_8PC+4 );
                    bs_write1( s, 0 ); // Cr = Cb
                }
                else
                {
                    scaling_list_write( s, pps, CQM_8IY+4 );
                    scaling_list_write( s, pps, CQM_8PY+4 );
                }
            }
        }
        bs_write_se( s, pps->i_chroma_qp_index_offset );
    }

	//RBSP拖尾  
    //无论比特流当前位置是否字节对齐 ， 都向其中写入一个比特1及若干个（0~7个）比特0 ， 使其字节对齐
    bs_rbsp_trailing( s );
    bs_flush( s );
}

2.3、x264_sei_version_write()函数

 

        x264_sei_version_write()用于输出SEI。SEI中一般存储了H.264中的一些附加信息，x264_sei_version_write()的定义位于encoder\set.c，x264_sei_version_write()首先调用了x264_param2string()将当前的配置参数保存到字符串opts[]中，然后调用sprintf()结合opt[]生成完整的SEI信息，最后调用x264_sei_write()输出SEI信息。在这个过程中涉及到一个libx264的API函数x264_param2string()。对应的代码如下：

 

////////////////输出SEI（其中包含了配置信息）
int x264_sei_version_write( x264_t *h, bs_t *s )
{
    // random ID number generated according to ISO-11578
    static const uint8_t uuid[16] =
    {
        0xdc, 0x45, 0xe9, 0xbd, 0xe6, 0xd9, 0x48, 0xb7,
        0x96, 0x2c, 0xd8, 0x20, 0xd9, 0x23, 0xee, 0xef
    };
    char *opts = x264_param2string( &h->param, 0 );//////////////把设置信息转换为字符串
    char *payload;
    int length;

    if( !opts )
        return -1;
    CHECKED_MALLOC( payload, 200 + strlen( opts ) );

    memcpy( payload, uuid, 16 );

	//配置信息的内容  
    //opts字符串内容还是挺多的
    sprintf( payload+16, "x264 - core %d%s - H.264/MPEG-4 AVC codec - "
             "Copy%s 2003-2016 - http://www.videolan.org/x264.html - options: %s",
             X264_BUILD, X264_VERSION, HAVE_GPL?"left":"right", opts );
    length = strlen(payload)+1;

	//输出SEI  
    //数据类型为USER_DATA_UNREGISTERED
    x264_sei_write( s, (uint8_t *)payload, length, SEI_USER_DATA_UNREGISTERED );

    x264_free( opts );
    x264_free( payload );
    return 0;
fail:
    x264_free( opts );
    return -1;
}

        其中，x264_param2string()用于将当前设置转换为字符串输出出来，x264_param2string()的定义位于common\common.c，可以看出x264_param2string()几乎遍历了libx264的所有设置选项，使用“s += sprintf()”的形式将它们连接成一个很长的字符串，并最终将该字符串返回。对应的代码如下：

 

/****************************************************************************
 * x264_param2string:
 ****************************************************************************/
//////////////////////把设置信息转换为字符串
char *x264_param2string( x264_param_t *p, int b_res )
{
    int len = 1000;
    char *buf, *s;
    if( p->rc.psz_zones )
        len += strlen(p->rc.psz_zones);
    buf = s = x264_malloc( len );
    if( !buf )
        return NULL;

    if( b_res )
    {
        s += sprintf( s, "%dx%d ", p->i_width, p->i_height );
        s += sprintf( s, "fps=%u/%u ", p->i_fps_num, p->i_fps_den );
        s += sprintf( s, "timebase=%u/%u ", p->i_timebase_num, p->i_timebase_den );
        s += sprintf( s, "bitdepth=%d ", BIT_DEPTH );
    }

    if( p->b_opencl )
        s += sprintf( s, "opencl=%d ", p->b_opencl );
    s += sprintf( s, "cabac=%d", p->b_cabac );
    s += sprintf( s, " ref=%d", p->i_frame_reference );
    s += sprintf( s, " deblock=%d:%d:%d", p->b_deblocking_filter,
                  p->i_deblocking_filter_alphac0, p->i_deblocking_filter_beta );
    s += sprintf( s, " analyse=%#x:%#x", p->analyse.intra, p->analyse.inter );
    s += sprintf( s, " me=%s", x264_motion_est_names[ p->analyse.i_me_method ] );
    s += sprintf( s, " subme=%d", p->analyse.i_subpel_refine );
    s += sprintf( s, " psy=%d", p->analyse.b_psy );
    if( p->analyse.b_psy )
        s += sprintf( s, " psy_rd=%.2f:%.2f", p->analyse.f_psy_rd, p->analyse.f_psy_trellis );
    s += sprintf( s, " mixed_ref=%d", p->analyse.b_mixed_references );
    s += sprintf( s, " me_range=%d", p->analyse.i_me_range );
    s += sprintf( s, " chroma_me=%d", p->analyse.b_chroma_me );
    s += sprintf( s, " trellis=%d", p->analyse.i_trellis );
    s += sprintf( s, " 8x8dct=%d", p->analyse.b_transform_8x8 );
    s += sprintf( s, " cqm=%d", p->i_cqm_preset );
    s += sprintf( s, " deadzone=%d,%d", p->analyse.i_luma_deadzone[0], p->analyse.i_luma_deadzone[1] );
    s += sprintf( s, " fast_pskip=%d", p->analyse.b_fast_pskip );
    s += sprintf( s, " chroma_qp_offset=%d", p->analyse.i_chroma_qp_offset );
    s += sprintf( s, " threads=%d", p->i_threads );
    s += sprintf( s, " lookahead_threads=%d", p->i_lookahead_threads );
    s += sprintf( s, " sliced_threads=%d", p->b_sliced_threads );
    if( p->i_slice_count )
        s += sprintf( s, " slices=%d", p->i_slice_count );
    if( p->i_slice_count_max )
        s += sprintf( s, " slices_max=%d", p->i_slice_count_max );
    if( p->i_slice_max_size )
        s += sprintf( s, " slice_max_size=%d", p->i_slice_max_size );
    if( p->i_slice_max_mbs )
        s += sprintf( s, " slice_max_mbs=%d", p->i_slice_max_mbs );
    if( p->i_slice_min_mbs )
        s += sprintf( s, " slice_min_mbs=%d", p->i_slice_min_mbs );
    s += sprintf( s, " nr=%d", p->analyse.i_noise_reduction );
    s += sprintf( s, " decimate=%d", p->analyse.b_dct_decimate );
    s += sprintf( s, " interlaced=%s", p->b_interlaced ? p->b_tff ? "tff" : "bff" : p->b_fake_interlaced ? "fake" : "0" );
    s += sprintf( s, " bluray_compat=%d", p->b_bluray_compat );
    if( p->b_stitchable )
        s += sprintf( s, " stitchable=%d", p->b_stitchable );

    s += sprintf( s, " constrained_intra=%d", p->b_constrained_intra );

    s += sprintf( s, " bframes=%d", p->i_bframe );
    if( p->i_bframe )
    {
        s += sprintf( s, " b_pyramid=%d b_adapt=%d b_bias=%d direct=%d weightb=%d open_gop=%d",
                      p->i_bframe_pyramid, p->i_bframe_adaptive, p->i_bframe_bias,
                      p->analyse.i_direct_mv_pred, p->analyse.b_weighted_bipred, p->b_open_gop );
    }
    s += sprintf( s, " weightp=%d", p->analyse.i_weighted_pred > 0 ? p->analyse.i_weighted_pred : 0 );

    if( p->i_keyint_max == X264_KEYINT_MAX_INFINITE )
        s += sprintf( s, " keyint=infinite" );
    else
        s += sprintf( s, " keyint=%d", p->i_keyint_max );
    s += sprintf( s, " keyint_min=%d scenecut=%d intra_refresh=%d",
                  p->i_keyint_min, p->i_scenecut_threshold, p->b_intra_refresh );

    if( p->rc.b_mb_tree || p->rc.i_vbv_buffer_size )
        s += sprintf( s, " rc_lookahead=%d", p->rc.i_lookahead );

    s += sprintf( s, " rc=%s mbtree=%d", p->rc.i_rc_method == X264_RC_ABR ?
                               ( p->rc.b_stat_read ? "2pass" : p->rc.i_vbv_max_bitrate == p->rc.i_bitrate ? "cbr" : "abr" )
                               : p->rc.i_rc_method == X264_RC_CRF ? "crf" : "cqp", p->rc.b_mb_tree );
    if( p->rc.i_rc_method == X264_RC_ABR || p->rc.i_rc_method == X264_RC_CRF )
    {
        if( p->rc.i_rc_method == X264_RC_CRF )
            s += sprintf( s, " crf=%.1f", p->rc.f_rf_constant );
        else
            s += sprintf( s, " bitrate=%d ratetol=%.1f",
                          p->rc.i_bitrate, p->rc.f_rate_tolerance );
        s += sprintf( s, " qcomp=%.2f qpmin=%d qpmax=%d qpstep=%d",
                      p->rc.f_qcompress, p->rc.i_qp_min, p->rc.i_qp_max, p->rc.i_qp_step );
        if( p->rc.b_stat_read )
            s += sprintf( s, " cplxblur=%.1f qblur=%.1f",
                          p->rc.f_complexity_blur, p->rc.f_qblur );
        if( p->rc.i_vbv_buffer_size )
        {
            s += sprintf( s, " vbv_maxrate=%d vbv_bufsize=%d",
                          p->rc.i_vbv_max_bitrate, p->rc.i_vbv_buffer_size );
            if( p->rc.i_rc_method == X264_RC_CRF )
                s += sprintf( s, " crf_max=%.1f", p->rc.f_rf_constant_max );
        }
    }
    else if( p->rc.i_rc_method == X264_RC_CQP )
        s += sprintf( s, " qp=%d", p->rc.i_qp_constant );

    if( p->rc.i_vbv_buffer_size )
        s += sprintf( s, " nal_hrd=%s filler=%d", x264_nal_hrd_names[p->i_nal_hrd], p->rc.b_filler );
    if( p->crop_rect.i_left | p->crop_rect.i_top | p->crop_rect.i_right | p->crop_rect.i_bottom )
        s += sprintf( s, " crop_rect=%u,%u,%u,%u", p->crop_rect.i_left, p->crop_rect.i_top,
                                                   p->crop_rect.i_right, p->crop_rect.i_bottom );
    if( p->i_frame_packing >= 0 )
        s += sprintf( s, " frame-packing=%d", p->i_frame_packing );

    if( !(p->rc.i_rc_method == X264_RC_CQP && p->rc.i_qp_constant == 0) )
    {
        s += sprintf( s, " ip_ratio=%.2f", p->rc.f_ip_factor );
        if( p->i_bframe && !p->rc.b_mb_tree )
            s += sprintf( s, " pb_ratio=%.2f", p->rc.f_pb_factor );
        s += sprintf( s, " aq=%d", p->rc.i_aq_mode );
        if( p->rc.i_aq_mode )
            s += sprintf( s, ":%.2f", p->rc.f_aq_strength );
        if( p->rc.psz_zones )
            s += sprintf( s, " zones=%s", p->rc.psz_zones );
        else if( p->rc.i_zones )
            s += sprintf( s, " zones" );
    }

    return buf;
}