H.264（H264）解碼SPS獲取解析度和幀率
阿新 • • 發佈：2019-01-27
timing_info_present_flag等於1表示num_units_in_tick，time_scale和fixed_frame_rate_flag在位元流中存在。#include <stdio.h> #include <stdint.h> #include <string.h> #include <math.h> typedef unsigned int UINT; typedef unsigned char BYTE; typedef unsigned long DWORD; UINT Ue(BYTE *pBuff, UINT nLen, UINT &nStartBit) { //計算0bit的個數 UINT nZeroNum = 0; while (nStartBit < nLen * 8) { if (pBuff[nStartBit / 8] & (0x80 >> (nStartBit % 8))) //&:按位與，%取餘 { break; } nZeroNum++; nStartBit++; } nStartBit ++; //計算結果 DWORD dwRet = 0; for (UINT i=0; i<nZeroNum; i++) { dwRet <<= 1; if (pBuff[nStartBit / 8] & (0x80 >> (nStartBit % 8))) { dwRet += 1; } nStartBit++; } return (1 << nZeroNum) - 1 + dwRet; } int Se(BYTE *pBuff, UINT nLen, UINT &nStartBit) { int UeVal=Ue(pBuff,nLen,nStartBit); double k=UeVal; int nValue=ceil(k/2);//ceil函式：ceil函式的作用是求不小於給定實數的最小整數。ceil(2)=ceil(1.2)=cei(1.5)=2.00 if (UeVal % 2==0) nValue=-nValue; return nValue; } DWORD u(UINT BitCount,BYTE * buf,UINT &nStartBit) { DWORD dwRet = 0; for (UINT i=0; i<BitCount; i++) { dwRet <<= 1; if (buf[nStartBit / 8] & (0x80 >> (nStartBit % 8))) { dwRet += 1; } nStartBit++; } return dwRet; } /** * H264的NAL起始碼防競爭機制 * * @param buf SPS資料內容 * * @無返回值 */ void de_emulation_prevention(BYTE* buf,unsigned int* buf_size) { int i=0,j=0; BYTE* tmp_ptr=NULL; unsigned int tmp_buf_size=0; int val=0; tmp_ptr=buf; tmp_buf_size=*buf_size; for(i=0;i<(tmp_buf_size-2);i++) { //check for 0x000003 val=(tmp_ptr[i]^0x00) +(tmp_ptr[i+1]^0x00)+(tmp_ptr[i+2]^0x03); if(val==0) { //kick out 0x03 for(j=i+2;j<tmp_buf_size-1;j++) tmp_ptr[j]=tmp_ptr[j+1]; //and so we should devrease bufsize (*buf_size)--; } } } /** * 解碼SPS,獲取視訊影象寬、高和幀率資訊 * * @param buf SPS資料內容 * @param nLen SPS資料的長度 * @param width 影象寬度 * @param height 影象高度 * @成功則返回true , 失敗則返回false */ bool h264_decode_sps(BYTE * buf,unsigned int nLen,int &width,int &height,int &fps) { UINT StartBit=0; fps=0; de_emulation_prevention(buf,&nLen); int forbidden_zero_bit=u(1,buf,StartBit); int nal_ref_idc=u(2,buf,StartBit); int nal_unit_type=u(5,buf,StartBit); if(nal_unit_type==7) { int profile_idc=u(8,buf,StartBit); int constraint_set0_flag=u(1,buf,StartBit);//(buf[1] & 0x80)>>7; int constraint_set1_flag=u(1,buf,StartBit);//(buf[1] & 0x40)>>6; int constraint_set2_flag=u(1,buf,StartBit);//(buf[1] & 0x20)>>5; int constraint_set3_flag=u(1,buf,StartBit);//(buf[1] & 0x10)>>4; int reserved_zero_4bits=u(4,buf,StartBit); int level_idc=u(8,buf,StartBit); int seq_parameter_set_id=Ue(buf,nLen,StartBit); if( profile_idc == 100 || profile_idc == 110 || profile_idc == 122 || profile_idc == 144 ) { int chroma_format_idc=Ue(buf,nLen,StartBit); if( chroma_format_idc == 3 ) int residual_colour_transform_flag=u(1,buf,StartBit); int bit_depth_luma_minus8=Ue(buf,nLen,StartBit); int bit_depth_chroma_minus8=Ue(buf,nLen,StartBit); int qpprime_y_zero_transform_bypass_flag=u(1,buf,StartBit); int seq_scaling_matrix_present_flag=u(1,buf,StartBit); int seq_scaling_list_present_flag[8]; if( seq_scaling_matrix_present_flag ) { for( int i = 0; i < 8; i++ ) { seq_scaling_list_present_flag[i]=u(1,buf,StartBit); } } } int log2_max_frame_num_minus4=Ue(buf,nLen,StartBit); int pic_order_cnt_type=Ue(buf,nLen,StartBit); if( pic_order_cnt_type == 0 ) int log2_max_pic_order_cnt_lsb_minus4=Ue(buf,nLen,StartBit); else if( pic_order_cnt_type == 1 ) { int delta_pic_order_always_zero_flag=u(1,buf,StartBit); int offset_for_non_ref_pic=Se(buf,nLen,StartBit); int offset_for_top_to_bottom_field=Se(buf,nLen,StartBit); int num_ref_frames_in_pic_order_cnt_cycle=Ue(buf,nLen,StartBit); int *offset_for_ref_frame=new int[num_ref_frames_in_pic_order_cnt_cycle]; for( int i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; i++ ) offset_for_ref_frame[i]=Se(buf,nLen,StartBit); delete [] offset_for_ref_frame; } int num_ref_frames=Ue(buf,nLen,StartBit); int gaps_in_frame_num_value_allowed_flag=u(1,buf,StartBit); int pic_width_in_mbs_minus1=Ue(buf,nLen,StartBit); int pic_height_in_map_units_minus1=Ue(buf,nLen,StartBit); width=(pic_width_in_mbs_minus1+1)*16; height=(pic_height_in_map_units_minus1+1)*16; int frame_mbs_only_flag=u(1,buf,StartBit); if(!frame_mbs_only_flag) int mb_adaptive_frame_field_flag=u(1,buf,StartBit); int direct_8x8_inference_flag=u(1,buf,StartBit); int frame_cropping_flag=u(1,buf,StartBit); if(frame_cropping_flag) { int frame_crop_left_offset=Ue(buf,nLen,StartBit); int frame_crop_right_offset=Ue(buf,nLen,StartBit); int frame_crop_top_offset=Ue(buf,nLen,StartBit); int frame_crop_bottom_offset=Ue(buf,nLen,StartBit); } int vui_parameter_present_flag=u(1,buf,StartBit); if(vui_parameter_present_flag) { int aspect_ratio_info_present_flag=u(1,buf,StartBit); if(aspect_ratio_info_present_flag) { int aspect_ratio_idc=u(8,buf,StartBit); if(aspect_ratio_idc==255) { int sar_width=u(16,buf,StartBit); int sar_height=u(16,buf,StartBit); } } int overscan_info_present_flag=u(1,buf,StartBit); if(overscan_info_present_flag) int overscan_appropriate_flagu=u(1,buf,StartBit); int video_signal_type_present_flag=u(1,buf,StartBit); if(video_signal_type_present_flag) { int video_format=u(3,buf,StartBit); int video_full_range_flag=u(1,buf,StartBit); int colour_description_present_flag=u(1,buf,StartBit); if(colour_description_present_flag) { int colour_primaries=u(8,buf,StartBit); int transfer_characteristics=u(8,buf,StartBit); int matrix_coefficients=u(8,buf,StartBit); } } int chroma_loc_info_present_flag=u(1,buf,StartBit); if(chroma_loc_info_present_flag) { int chroma_sample_loc_type_top_field=Ue(buf,nLen,StartBit); int chroma_sample_loc_type_bottom_field=Ue(buf,nLen,StartBit); } int timing_info_present_flag=u(1,buf,StartBit); if(timing_info_present_flag) { int num_units_in_tick=u(32,buf,StartBit); int time_scale=u(32,buf,StartBit); fps=time_scale/num_units_in_tick; int fixed_frame_rate_flag=u(1,buf,StartBit); if(fixed_frame_rate_flag) { fps=fps/2; } } } return true; } else return false; }
timing_info_present_flag等於0表示num_units_in_tick，time_scale和fixed_frame_rate_flag在位元流中不存在。
因此，當timing_info_present_flag等於0時，無法得到位元速率，bool h264_decode_sps(BYTE * buf,unsigned int nLen,int &width,int &height,int &fps)引數fps返回值為0，可據此設定一個預設幀率。
