H264参数语法文档： SPS、PPS、IDR

H.264码流第一个 NALU 是 SPS（序列参数集Sequence Parameter Set）
对应H264标准文档 7.3.2.1 序列参数集的语法进行解析

SPS参数解析// fill sps with content of p

int InterpretSPS (VideoParameters *p_Vid, DataPartition *p, seq_parameter_set_rbsp_t *sps)
{
  unsigned i;
  unsigned n_ScalingList;
  int reserved_zero;
  Bitstream *s = p->bitstream;

  assert (p != NULL);
  assert (p->bitstream != NULL);
  assert (p->bitstream->streamBuffer != 0);
  assert (sps != NULL);

  p_Dec->UsedBits = 0;

  sps->profile_idc                            = u_v  (8, "SPS: profile_idc"                           , s);

  if ((sps->profile_idc!=BASELINE       ) &&
      (sps->profile_idc!=MAIN           ) &&
      (sps->profile_idc!=EXTENDED       ) &&
      (sps->profile_idc!=FREXT_HP       ) &&
      (sps->profile_idc!=FREXT_Hi10P    ) &&
      (sps->profile_idc!=FREXT_Hi422    ) &&
      (sps->profile_idc!=FREXT_Hi444    ) &&
      (sps->profile_idc!=FREXT_CAVLC444 )
#if (MVC_EXTENSION_ENABLE)
      && (sps->profile_idc!=MVC_HIGH)
      && (sps->profile_idc!=STEREO_HIGH)
#endif
      )
  {
    printf("Invalid Profile IDC (%d) encountered. /n", sps->profile_idc);
    return p_Dec->UsedBits;
  }

  sps->constrained_set0_flag                  = u_1  (   "SPS: constrained_set0_flag"                 , s);
  sps->constrained_set1_flag                  = u_1  (   "SPS: constrained_set1_flag"                 , s);
  sps->constrained_set2_flag                  = u_1  (   "SPS: constrained_set2_flag"                 , s);
  sps->constrained_set3_flag                  = u_1  (   "SPS: constrained_set3_flag"                 , s);
#if (MVC_EXTENSION_ENABLE)
  sps->constrained_set4_flag                  = u_1  (   "SPS: constrained_set4_flag"                 , s);
  reserved_zero                               = u_v  (3, "SPS: reserved_zero_3bits"                   , s);
#else
  reserved_zero                               = u_v  (4, "SPS: reserved_zero_4bits"                   , s);
#endif
  assert (reserved_zero==0);

  sps->level_idc                              = u_v  (8, "SPS: level_idc"                             , s);

  sps->seq_parameter_set_id                   = ue_v ("SPS: seq_parameter_set_id"                     , s);

  // Fidelity Range Extensions stuff
  sps->chroma_format_idc = 1;
  sps->bit_depth_luma_minus8   = 0;
  sps->bit_depth_chroma_minus8 = 0;
  p_Vid->lossless_qpprime_flag   = 0;
  sps->separate_colour_plane_flag = 0;

  if((sps->profile_idc==FREXT_HP   ) ||
     (sps->profile_idc==FREXT_Hi10P) ||
     (sps->profile_idc==FREXT_Hi422) ||
     (sps->profile_idc==FREXT_Hi444) ||
     (sps->profile_idc==FREXT_CAVLC444)
#if (MVC_EXTENSION_ENABLE)
     || (sps->profile_idc==MVC_HIGH)
     || (sps->profile_idc==STEREO_HIGH)
#endif
     )
  {
    sps->chroma_format_idc                      = ue_v ("SPS: chroma_format_idc"                       , s);

    if(sps->chroma_format_idc == YUV444)
    {
      sps->separate_colour_plane_flag           = u_1  ("SPS: separate_colour_plane_flag"              , s);
    }

    sps->bit_depth_luma_minus8                  = ue_v ("SPS: bit_depth_luma_minus8"                   , s);
    sps->bit_depth_chroma_minus8                = ue_v ("SPS: bit_depth_chroma_minus8"                 , s);
    //checking;
    if((sps->bit_depth_luma_minus8+8 > sizeof(imgpel)*8) || (sps->bit_depth_chroma_minus8+8> sizeof(imgpel)*8))
      error ("Source picture has higher bit depth than imgpel data type. /nPlease recompile with larger data type for imgpel.", 500);

    p_Vid->lossless_qpprime_flag                  = u_1  ("SPS: lossless_qpprime_y_zero_flag"            , s);

    sps->seq_scaling_matrix_present_flag        = u_1  (   "SPS: seq_scaling_matrix_present_flag"       , s);
    
    if(sps->seq_scaling_matrix_present_flag)
    {
      n_ScalingList = (sps->chroma_format_idc != YUV444) ? 8 : 12;
      for(i=0; iseq_scaling_list_present_flag[i]   = u_1  (   "SPS: seq_scaling_list_present_flag"         , s);
        if(sps->seq_scaling_list_present_flag[i])
        {
          if(i<6) scaling_list="">ScalingList4x4[i], 16, &sps->UseDefaultScalingMatrix4x4Flag[i], s);
          else
            Scaling_List(sps->ScalingList8x8[i-6], 64, &sps->UseDefaultScalingMatrix8x8Flag[i-6], s);
        }
      }
    }
  }

  sps->log2_max_frame_num_minus4              = ue_v ("SPS: log2_max_frame_num_minus4"                , s);
  sps->pic_order_cnt_type                     = ue_v ("SPS: pic_order_cnt_type"                       , s);

  if (sps->pic_order_cnt_type == 0)
    sps->log2_max_pic_order_cnt_lsb_minus4 = ue_v ("SPS: log2_max_pic_order_cnt_lsb_minus4"           , s);
  else if (sps->pic_order_cnt_type == 1)
  {
    sps->delta_pic_order_always_zero_flag      = u_1  ("SPS: delta_pic_order_always_zero_flag"       , s);
    sps->offset_for_non_ref_pic                = se_v ("SPS: offset_for_non_ref_pic"                 , s);
    sps->offset_for_top_to_bottom_field        = se_v ("SPS: offset_for_top_to_bottom_field"         , s);
    sps->num_ref_frames_in_pic_order_cnt_cycle = ue_v ("SPS: num_ref_frames_in_pic_order_cnt_cycle"  , s);
    for(i=0; inum_ref_frames_in_pic_order_cnt_cycle; i++)
      sps->offset_for_ref_frame[i]               = se_v ("SPS: offset_for_ref_frame[i]"              , s);
  }
  sps->num_ref_frames                        = ue_v ("SPS: num_ref_frames"                         , s);
  sps->gaps_in_frame_num_value_allowed_flag  = u_1  ("SPS: gaps_in_frame_num_value_allowed_flag"   , s);
  sps->pic_width_in_mbs_minus1               = ue_v ("SPS: pic_width_in_mbs_minus1"                , s);
  sps->pic_height_in_map_units_minus1        = ue_v ("SPS: pic_height_in_map_units_minus1"         , s);
  sps->frame_mbs_only_flag                   = u_1  ("SPS: frame_mbs_only_flag"                    , s);
  if (!sps->frame_mbs_only_flag)
  {
    sps->mb_adaptive_frame_field_flag        = u_1  ("SPS: mb_adaptive_frame_field_flag"           , s);
  }
  sps->direct_8x8_inference_flag             = u_1  ("SPS: direct_8x8_inference_flag"              , s);
  sps->frame_cropping_flag                   = u_1  ("SPS: frame_cropping_flag"                    , s);

  if (sps->frame_cropping_flag)
  {
    sps->frame_cropping_rect_left_offset      = ue_v ("SPS: frame_cropping_rect_left_offset"           , s);
    sps->frame_cropping_rect_right_offset     = ue_v ("SPS: frame_cropping_rect_right_offset"          , s);
    sps->frame_cropping_rect_top_offset       = ue_v ("SPS: frame_cropping_rect_top_offset"            , s);
    sps->frame_cropping_rect_bottom_offset    = ue_v ("SPS: frame_cropping_rect_bottom_offset"         , s);
  }
  sps->vui_parameters_present_flag           = (Boolean) u_1  ("SPS: vui_parameters_present_flag"      , s);

  InitVUI(sps);
  ReadVUI(p, sps);

  sps->Valid = TRUE;
  return p_Dec->UsedBits;
}

H.264码流第二个 NALU 是 PPS（图像参数集Picture Parameter Set）
对应H264标准文档 7.3.2.2 序列参数集的语法进行解析

PPS参数解析

int InterpretPPS (VideoParameters *p_Vid, DataPartition *p, pic_parameter_set_rbsp_t *pps)
{
  unsigned i;
  unsigned n_ScalingList;
  int chroma_format_idc;
  int NumberBitsPerSliceGroupId;
  Bitstream *s = p->bitstream;

  assert (p != NULL);
  assert (p->bitstream != NULL);
  assert (p->bitstream->streamBuffer != 0);
  assert (pps != NULL);

  p_Dec->UsedBits = 0;

  pps->pic_parameter_set_id                  = ue_v ("PPS: pic_parameter_set_id"                   , s);
  pps->seq_parameter_set_id                  = ue_v ("PPS: seq_parameter_set_id"                   , s);
  pps->entropy_coding_mode_flag              = u_1  ("PPS: entropy_coding_mode_flag"               , s);

  //! Note: as per JVT-F078 the following bit is unconditional.  If F078 is not accepted, then
  //! one has to fetch the correct SPS to check whether the bit is present (hopefully there is
  //! no consistency problem :-(
  //! The current encoder code handles this in the same way.  When you change this, don't forget
  //! the encoder!  StW, 12/8/02
  pps->bottom_field_pic_order_in_frame_present_flag                = u_1  ("PPS: bottom_field_pic_order_in_frame_present_flag"                 , s);

  pps->num_slice_groups_minus1               = ue_v ("PPS: num_slice_groups_minus1"                , s);

  // FMO stuff begins here
  if (pps->num_slice_groups_minus1 > 0)
  {
    pps->slice_group_map_type               = ue_v ("PPS: slice_group_map_type"                , s);
    if (pps->slice_group_map_type == 0)
    {
      for (i=0; i<=pps->num_slice_groups_minus1; i++)
        pps->run_length_minus1 [i]                  = ue_v ("PPS: run_length_minus1 [i]"              , s);
    }
    else if (pps->slice_group_map_type == 2)
    {
      for (i=0; inum_slice_groups_minus1; i++)
      {
        //! JVT-F078: avoid reference of SPS by using ue(v) instead of u(v)
        pps->top_left [i]                          = ue_v ("PPS: top_left [i]"                        , s);
        pps->bottom_right [i]                      = ue_v ("PPS: bottom_right [i]"                    , s);
      }
    }
    else if (pps->slice_group_map_type == 3 ||
             pps->slice_group_map_type == 4 ||
             pps->slice_group_map_type == 5)
    {
      pps->slice_group_change_direction_flag     = u_1  ("PPS: slice_group_change_direction_flag"      , s);
      pps->slice_group_change_rate_minus1        = ue_v ("PPS: slice_group_change_rate_minus1"         , s);
    }
    else if (pps->slice_group_map_type == 6)
    {
      if (pps->num_slice_groups_minus1+1 >4)
        NumberBitsPerSliceGroupId = 3;
      else if (pps->num_slice_groups_minus1+1 > 2)
        NumberBitsPerSliceGroupId = 2;
      else
        NumberBitsPerSliceGroupId = 1;
      pps->pic_size_in_map_units_minus1      = ue_v ("PPS: pic_size_in_map_units_minus1"               , s);
      if ((pps->slice_group_id = calloc (pps->pic_size_in_map_units_minus1+1, 1)) == NULL)
        no_mem_exit ("InterpretPPS: slice_group_id");
      for (i=0; i<=pps->pic_size_in_map_units_minus1; i++)
        pps->slice_group_id[i] = (byte) u_v (NumberBitsPerSliceGroupId, "slice_group_id[i]", s);
    }
  }

  // End of FMO stuff

  pps->num_ref_idx_l0_active_minus1          = ue_v ("PPS: num_ref_idx_l0_active_minus1"           , s);
  pps->num_ref_idx_l1_active_minus1          = ue_v ("PPS: num_ref_idx_l1_active_minus1"           , s);
  pps->weighted_pred_flag                    = u_1  ("PPS: weighted_pred_flag"                     , s);
  pps->weighted_bipred_idc                   = u_v  ( 2, "PPS: weighted_bipred_idc"                , s);
  pps->pic_init_qp_minus26                   = se_v ("PPS: pic_init_qp_minus26"                    , s);
  pps->pic_init_qs_minus26                   = se_v ("PPS: pic_init_qs_minus26"                    , s);

  pps->chroma_qp_index_offset                = se_v ("PPS: chroma_qp_index_offset"                 , s);

  pps->deblocking_filter_control_present_flag = u_1 ("PPS: deblocking_filter_control_present_flag" , s);
  pps->constrained_intra_pred_flag           = u_1  ("PPS: constrained_intra_pred_flag"            , s);
  pps->redundant_pic_cnt_present_flag        = u_1  ("PPS: redundant_pic_cnt_present_flag"         , s);

  if(more_rbsp_data(s->streamBuffer, s->frame_bitoffset,s->bitstream_length)) // more_data_in_rbsp()
  {
    //Fidelity Range Extensions Stuff
    pps->transform_8x8_mode_flag           = u_1  ("PPS: transform_8x8_mode_flag"                , s);
    pps->pic_scaling_matrix_present_flag   =  u_1  ("PPS: pic_scaling_matrix_present_flag"        , s);

    if(pps->pic_scaling_matrix_present_flag)
    {
      chroma_format_idc = p_Vid->SeqParSet[pps->seq_parameter_set_id].chroma_format_idc;
      n_ScalingList = 6 + ((chroma_format_idc != YUV444) ? 2 : 6) * pps->transform_8x8_mode_flag;
      for(i=0; ipic_scaling_list_present_flag[i]= u_1  ("PPS: pic_scaling_list_present_flag"          , s);

        if(pps->pic_scaling_list_present_flag[i])
        {
          if(i<6) scaling_list="">ScalingList4x4[i], 16, &pps->UseDefaultScalingMatrix4x4Flag[i], s);
          else
            Scaling_List(pps->ScalingList8x8[i-6], 64, &pps->UseDefaultScalingMatrix8x8Flag[i-6], s);
        }
      }
    }
    pps->second_chroma_qp_index_offset      = se_v ("PPS: second_chroma_qp_index_offset"          , s);
  }
  else
  {
    pps->second_chroma_qp_index_offset      = pps->chroma_qp_index_offset;
  }

  pps->Valid = TRUE;
  return p_Dec->UsedBits;
}

H.264码流第三个 NALU 是 IDR（即时解码器刷新）
对应H264标准文档 7.3.3 序列参数集的语法进行解析

IDR参数解析

case NALU_TYPE_IDR:
        img->idr_flag = (nalu->nal_unit_type == NALU_TYPE_IDR);
        img->nal_reference_idc = nalu->nal_reference_idc;
        img->disposable_flag = (nalu->nal_reference_idc == NALU_PRIORITY_DISPOSABLE);
        currSlice->dp_mode = PAR_DP_1;	//++ dp_mode：数据分割模式；PAR_DP_1=0：没有数据分割
        currSlice->max_part_nr = 1;
        currSlice->ei_flag = 0;	//++ 该处赋值直接影响decode_slice()函数中对decode_one_slice()函数的调用
									//++ 该值不为0，表明当前片出错，解码程序将忽略当前片的解码过程，而使用错误隐藏
        currStream = currSlice->partArr[0].bitstream;
        currStream->ei_flag = 0;	//++ 此处的赋值为最终赋值，以后不再改变。该值将对每个宏块的ei_flag产生影响
									//++ 参见macroblock.c文件read_one_macroblock()函数的如下语句：
									//++		:if(!dP->bitstream->ei_flag)		:currMB->ei_flag = 0;
									//++ 该值还在macroblock.c文件if(IS_INTRA (currMB) && dP->bitstream->ei_flag && img->number)中用到
        currStream->frame_bitoffset = currStream->read_len = 0;
        memcpy (currStream->streamBuffer, &nalu->buf[1], nalu->len-1);
        currStream->code_len = currStream->bitstream_length = RBSPtoSODB(currStream->streamBuffer, nalu->len-1);

        // Some syntax of the Slice Header depends on the parameter set, which depends on
        // the parameter set ID of the SLice header.  Hence, read the pic_parameter_set_id
        // of the slice header first, then setup the active parameter sets, and then read
        // the rest of the slice header
        BitsUsedByHeader = FirstPartOfSliceHeader();	//++ 参见标准7.3.3
        UseParameterSet (currSlice->pic_parameter_set_id);
        BitsUsedByHeader+= RestOfSliceHeader ();	//++ 参见标准7.3.3
		//++ BitsUsedByHeader在程序中没有实际用处，而且BitsUsedByHeader+= RestOfSliceHeader ()
		//++ 重复计算了FirstPartOfSliceHeader()所用到的比特数。因为在FirstPartOfSliceHeader()
		//++ 之后，变量UsedBits值并未被置零就代入RestOfSliceHeader()运算，从而RestOfSliceHeader ()
		//++ 在返回时，BitsUsedByHeader+= RestOfSliceHeader()多加了一个BitsUsedByHeader值

        FmoInit (active_pps, active_sps);

        if(is_new_picture())
        {
          init_picture(img, input);
          
          current_header = SOP;
          //check zero_byte if it is also the first NAL unit in the access unit
          CheckZeroByteVCL(nalu, &ret);
        }
        else
          current_header = SOS;
  
        init_lists(img->type, img->currentSlice->structure);
        reorder_lists (img->type, img->currentSlice);

        if (img->structure==FRAME)
        {
          init_mbaff_lists();
        }

/*        if (img->frame_num==1) // write a reference list
        {
          count ++;
          if (count==1)
            for (i=0; i

        // From here on, active_sps, active_pps and the slice header are valid
        if (img->MbaffFrameFlag)
          img->current_mb_nr = currSlice->start_mb_nr << 1="" style="color: #0000ff">else
          img->current_mb_nr = currSlice->start_mb_nr;

        if (active_pps->entropy_coding_mode_flag)
        {
          int ByteStartPosition = currStream->frame_bitoffset/8;
          if (currStream->frame_bitoffset%8 != 0) 
          {
            ByteStartPosition++;
          }
          arideco_start_decoding (&currSlice->partArr[0].de_cabac, currStream->streamBuffer, ByteStartPosition, &currStream->read_len, img->type);
        }
// printf ("read_new_slice: returning %s/n", current_header == SOP?"SOP":"SOS");
        FreeNALU(nalu);
        return current_header;
        break;
      case NALU_TYPE_DPA:
        //! The state machine here should follow the same ideas as the old readSliceRTP()
        //! basically:
        //! work on DPA (as above)
        //! read and process all following SEI/SPS/PPS/PD/Filler NALUs
        //! if next video NALU is dpB, 
        //!   then read and check whether it belongs to DPA, if yes, use it
        //! else
        //!   ;   // nothing
        //! read and process all following SEI/SPS/PPS/PD/Filler NALUs
        //! if next video NALU is dpC
        //!   then read and check whether it belongs to DPA (and DPB, if present), if yes, use it, done
        //! else
        //!   use the DPA (and the DPB if present)

        /* 
            LC: inserting the code related to DP processing, mainly copying some of the parts
            related to NALU_TYPE_SLICE, NALU_TYPE_IDR.
        */

        if(expected_slice_type != NALU_TYPE_DPA)
        {
          /* oops... we found the next slice, go back! */
          fseek(bits, ftell_position, SEEK_SET);
          FreeNALU(nalu);
          return current_header;
        }

        img->idr_flag          = (nalu->nal_unit_type == NALU_TYPE_IDR);
        img->nal_reference_idc = nalu->nal_reference_idc;
        img->disposable_flag   = (nalu->nal_reference_idc == NALU_PRIORITY_DISPOSABLE);
        currSlice->dp_mode     = PAR_DP_3;
        currSlice->max_part_nr = 3;
        currSlice->ei_flag     = 0;
        currStream             = currSlice->partArr[0].bitstream;
        currStream->ei_flag    = 0;
        currStream->frame_bitoffset = currStream->read_len = 0;
        memcpy (currStream->streamBuffer, &nalu->buf[1], nalu->len-1);
        currStream->code_len = currStream->bitstream_length = RBSPtoSODB(currStream->streamBuffer, nalu->len-1);	//++ 剔除停止比特和填充比特
        
        BitsUsedByHeader     = FirstPartOfSliceHeader();
        UseParameterSet (currSlice->pic_parameter_set_id);
        BitsUsedByHeader    += RestOfSliceHeader ();
        
        FmoInit (active_pps, active_sps);

        if(is_new_picture())
        {
          init_picture(img, input);
          current_header = SOP;
          CheckZeroByteVCL(nalu, &ret);
        }
        else
          current_header = SOS;

        
        init_lists(img->type, img->currentSlice->structure);
        reorder_lists (img->type, img->currentSlice);
        
        if (img->structure==FRAME)
        {
          init_mbaff_lists();
        }

        // From here on, active_sps, active_pps and the slice header are valid
        if (img->MbaffFrameFlag)
          img->current_mb_nr = currSlice->start_mb_nr << 1="" style="color: #0000ff">else
 
         img->current_mb_nr = currSlice->start_mb_nr;


        /* 
           LC:
              Now I need to read the slice ID, which depends on the value of 
              redundant_pic_cnt_present_flag (pag.49). 
        */

        slice_id_a  = ue_v("NALU:SLICE_A slice_idr", currStream);
        if (active_pps->entropy_coding_mode_flag)
        {
          int ByteStartPosition = currStream->frame_bitoffset/8;
          if (currStream->frame_bitoffset%8 != 0) 
          {
            ByteStartPosition++;
          }
          arideco_start_decoding (&currSlice->partArr[0].de_cabac, currStream->streamBuffer, ByteStartPosition, &currStream->read_len, img->type);
        }
// printf ("read_new_slice: returning %s/n", current_header == SOP?"SOP":"SOS");
        break;
      case NALU_TYPE_DPB:
        /* LC: inserting the code related to DP processing */

        currStream             = currSlice->partArr[1].bitstream;
        currStream->ei_flag    = 0;
        currStream->frame_bitoffset = currStream->read_len = 0;
        memcpy (currStream->streamBuffer, &nalu->buf[1], nalu->len-1);
        currStream->code_len = currStream->bitstream_length = RBSPtoSODB(currStream->streamBuffer, nalu->len-1);

        slice_id_b  = ue_v("NALU:SLICE_B slice_idr", currStream);
        if (active_pps->redundant_pic_cnt_present_flag)
          redundant_pic_cnt_b = ue_v("NALU:SLICE_B redudand_pic_cnt", currStream);
        else
          redundant_pic_cnt_b = 0;
        
        /*  LC: Initializing CABAC for the current data stream. */

        if (active_pps->entropy_coding_mode_flag)
        {
          int ByteStartPosition = currStream->frame_bitoffset/8;
          if (currStream->frame_bitoffset % 8 != 0) 
            ByteStartPosition++;
          
          arideco_start_decoding (&currSlice->partArr[1].de_cabac, currStream->streamBuffer, 
            ByteStartPosition, &currStream->read_len, img->type);
          
        }

        /* LC: resilience code to be inserted */
        /*         FreeNALU(nalu); */
        /*         return current_header; */

        break;

IDR参数解析/*!

 ************************************************************************
 * /brief
 *    read the first part of the header (only the pic_parameter_set_id)
 * /return
 *    Length of the first part of the slice header (in bits)
 ************************************************************************
 */
//++ 参见标准7.3.3
int FirstPartOfSliceHeader()
{
  Slice *currSlice = img->currentSlice;
  int dP_nr = assignSE2partition[currSlice->dp_mode][SE_HEADER];
  DataPartition *partition = &(currSlice->partArr[dP_nr]);
  Bitstream *currStream = partition->bitstream;
  int tmp;

  UsedBits= partition->bitstream->frame_bitoffset; // was hardcoded to 31 for previous start-code. This is better.

  // Get first_mb_in_slice
  currSlice->start_mb_nr = ue_v ("SH: first_mb_in_slice", currStream);

  tmp = ue_v ("SH: slice_type", currStream);
  
  if (tmp>4) tmp -=5;

  img->type = currSlice->picture_type = (SliceType) tmp;

  currSlice->pic_parameter_set_id = ue_v ("SH: pic_parameter_set_id", currStream);
  
  return UsedBits;
}