本文共 8390 字，大约阅读时间需要 27 分钟。

       先看lencod.c中的GenerateParameterSets函数，进入其中：

void GenerateParameterSets (){  seq_parameter_set_rbsp_t *sps = NULL;   pic_parameter_set_rbsp_t *pps = NULL;  sps = AllocSPS();  // 分配堆空间  pps = AllocPPS();  // 分配堆空间  FillParameterSetStructures (sps, pps);    active_sps = sps; // active_sps和下面的active_pps都是global.h中定义的全局变量  active_pps = pps;}

      进入FillParameterSetStructures函数看看：

void FillParameterSetStructures (seq_parameter_set_rbsp_t *sps,                                  pic_parameter_set_rbsp_t *pps){  unsigned i;  // *************************************************************************  // Sequence Parameter Set  // *************************************************************************  assert (sps != NULL);  assert (pps != NULL);  // Profile and Level should be calculated using the info from the config  // file.  Calculation is hidden in IndetifyProfile() and IdentifyLevel()  sps->profile_idc = IdentifyProfile();  sps->level_idc = IdentifyLevel();  // needs to be set according to profile  sps->constrained_set0_flag = 0;  sps->constrained_set1_flag = 0;  sps->constrained_set2_flag = 0;  // Parameter Set ID hardcoded to zero  sps->seq_parameter_set_id = 0;  //! POC stuff:  //! The following values are hard-coded in init_poc().  Apparently,  //! the poc implementation covers only a subset of the poc functionality.  //! Here, the same subset is implemented.  Changes in the POC stuff have  //! also to be reflected here  sps->log2_max_frame_num_minus4 = log2_max_frame_num_minus4;  sps->log2_max_pic_order_cnt_lsb_minus4 = log2_max_pic_order_cnt_lsb_minus4;    sps->pic_order_cnt_type = input->pic_order_cnt_type;  sps->num_ref_frames_in_pic_order_cnt_cycle = img->num_ref_frames_in_pic_order_cnt_cycle;  sps->delta_pic_order_always_zero_flag = img->delta_pic_order_always_zero_flag;  sps->offset_for_non_ref_pic = img->offset_for_non_ref_pic;  sps->offset_for_top_to_bottom_field = img->offset_for_top_to_bottom_field;  for (i=0; i
   
    num_ref_frames_in_pic_order_cnt_cycle; i++)  {    sps->offset_for_ref_frame[i] = img->offset_for_ref_frame[i];  }  // End of POC stuff  // Number of Reference Frames  sps->num_ref_frames = IdentifyNumRefFrames();  //required_frame_num_update_behaviour_flag hardcoded to zero  sps->gaps_in_frame_num_value_allowed_flag = FALSE;    // double check  sps->frame_mbs_only_flag = !(input->PicInterlace || input->MbInterlace);  // Picture size, finally a simple one :-)  sps->pic_width_in_mbs_minus1 = (input->img_width/16) -1;  sps->pic_height_in_map_units_minus1 = ((input->img_height/16)/ (2 - sps->frame_mbs_only_flag)) - 1;  // a couple of flags, simple  sps->mb_adaptive_frame_field_flag = (FRAME_CODING != input->MbInterlace);  sps->direct_8x8_inference_flag = input->directInferenceFlag;  // Sequence VUI not implemented, signalled as not present  sps->vui_parameters_present_flag = FALSE;    {    int PicWidthInMbs, PicHeightInMapUnits, FrameHeightInMbs;    int width, height;    PicWidthInMbs = (sps->pic_width_in_mbs_minus1 +1);    PicHeightInMapUnits = (sps->pic_height_in_map_units_minus1 +1);    FrameHeightInMbs = ( 2 - sps->frame_mbs_only_flag ) * PicHeightInMapUnits;        width = PicWidthInMbs * MB_BLOCK_SIZE;    height = FrameHeightInMbs * MB_BLOCK_SIZE;        Co_located = alloc_colocated (width, height,sps->mb_adaptive_frame_field_flag);      }  // *************************************************************************  // Picture Parameter Set   // *************************************************************************  pps->seq_parameter_set_id = 0;  pps->pic_parameter_set_id = 0;  pps->entropy_coding_mode_flag = (input->symbol_mode==UVLC?0:1);  // JVT-Fxxx (by Stephan Wenger, make this flag unconditional  pps->pic_order_present_flag = img->pic_order_present_flag;  // Begin FMO stuff  pps->num_slice_groups_minus1 = input->num_slice_groups_minus1;	  //! Following set the parameter for different slice group types  if (pps->num_slice_groups_minus1 > 0)    switch (input->slice_group_map_type)    {    case 0:			      pps->slice_group_map_type = 0;      for(i=0; i<=pps->num_slice_groups_minus1; i++)      {        pps->run_length_minus1[i]=input->run_length_minus1[i];      }			      break;    case 1:      pps->slice_group_map_type = 1;      break;    case 2:      // i loops from 0 to num_slice_groups_minus1-1, because no info for background needed      pps->slice_group_map_type = 2;      for(i=0; i
    
     num_slice_groups_minus1; i++)      {        pps->top_left[i] = input->top_left[i];        pps->bottom_right[i] = input->bottom_right[i];            }     break;    case 3:    case 4:    case 5:      pps->slice_group_map_type = input->slice_group_map_type;			      pps->slice_group_change_direction_flag = input->slice_group_change_direction_flag;      pps->slice_group_change_rate_minus1 = input->slice_group_change_rate_minus1;      break;    case 6:      pps->slice_group_map_type = 6;         pps->pic_size_in_map_units_minus1 = 				((input->img_height/MB_BLOCK_SIZE)/(2-sps->frame_mbs_only_flag))				*(input->img_width/MB_BLOCK_SIZE) -1;			      for (i=0;i<=pps->pic_size_in_map_units_minus1; i++)        pps->slice_group_id[i] = input->slice_group_id[i];			      break;    default:      printf ("Parset.c: slice_group_map_type invalid, default\n");      assert (0==1);    }// End FMO stuff  pps->num_ref_idx_l0_active_minus1 = sps->frame_mbs_only_flag ? (sps->num_ref_frames-1) : (2 * sps->num_ref_frames - 1) ;   // set defaults  pps->num_ref_idx_l1_active_minus1 = sps->frame_mbs_only_flag ? (sps->num_ref_frames-1) : (2 * sps->num_ref_frames - 1) ;   // set defaults  //pps->num_ref_idx_l1_active_minus1 = sps->frame_mbs_only_flag ? 0 : 1 ;   // set defaults    pps->weighted_pred_flag = input->WeightedPrediction;  pps->weighted_bipred_idc = input->WeightedBiprediction;  pps->pic_init_qp_minus26 = 0;         // hard coded to zero, QP lives in the slice header  pps->pic_init_qs_minus26 = 0;  pps->chroma_qp_index_offset = input->chroma_qp_index_offset;      // double check: is this chroma fidelity thing already implemented???  pps->deblocking_filter_control_present_flag = input->LFSendParameters;  pps->constrained_intra_pred_flag = input->UseConstrainedIntraPred;    pps->redundant_pic_cnt_present_flag = 0;  // the picture vui consists currently of the cropping rectangle, which cannot  // used by the current decoder and hence is never sent.  sps->frame_cropping_flag = FALSE;};
    
   

      可见，FillParameterSetStructures函数的作用是对sps->...和pps->...进行赋值，其中很多值都是从input->...和img->...中得到的，而后两者中的很多值是从配置文件中得到的. 经过对active_sps和active_pps赋值后，active_sps和active_pps就得到了相应的值（有些是间接从配置文件中获得的）

 

      继续看start_sequence函数：

int start_sequence(){  int len=0;  NALU_t *nalu;  switch(input->of_mode)  {    case PAR_OF_ANNEXB:      OpenAnnexbFile (input->outfile);      WriteNALU = WriteAnnexbNALU;      break;    case PAR_OF_RTP:      OpenRTPFile (input->outfile);      WriteNALU = WriteRTPNALU;      break;    default:      snprintf(errortext, ET_SIZE, "Output File Mode %d not supported", input->of_mode);      error(errortext,1);      return 1;  }  //! As a sequence header, here we write the both sequence and picture  //! parameter sets.  As soon as IDR is implemented, this should go to the  //! IDR part, as both parsets have to be transmitted as part of an IDR.  //! An alterbative may be to consider this function the IDR start function.    nalu = NULL;  nalu = GenerateSeq_parameter_set_NALU ();  len += WriteNALU (nalu);  FreeNALU (nalu);  nalu = NULL;  nalu = GeneratePic_parameter_set_NALU ();  len += WriteNALU (nalu);  FreeNALU (nalu);//  stat->bit_ctr_parametersets = len;    stat->bit_ctr_parametersets_n = len;  return 0;}

      进入GenerateSeq_parameter_set_NALU函数看看：

NALU_t *GenerateSeq_parameter_set_NALU (){  NALU_t *n = AllocNALU(64000);  int RBSPlen = 0;  int NALUlen;  byte rbsp[MAXRBSPSIZE];  RBSPlen = GenerateSeq_parameter_set_rbsp (active_sps, rbsp);  NALUlen = RBSPtoNALU (rbsp, n, RBSPlen, NALU_TYPE_SPS, NALU_PRIORITY_HIGHEST, 0, 1);  n->startcodeprefix_len = 4;  return n;}

     由RBSPlen = GenerateSeq_parameter_set_rbsp (active_sps, rbsp);可知，在生成RBSP的过程中，的确用到了active_sps(间接地从配置文件获得了数据). 随后RBSP又转换成了NALU,这样就生成了一个NALU(这样，NALU就间接地从配置文件获得了数据)

 

     于是start_sequence函数中的下面语句就生成了sps对应的NALU和pps对应的NALU:

nalu = GenerateSeq_parameter_set_NALU ();......nalu = GeneratePic_parameter_set_NALU ();

     于是，调用start_sequence函数中的下面语句后，就把SPS呵呵PPS写进码流了:

len += WriteNALU (nalu);......len += WriteNALU (nalu);

 

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