解析H264的SPS信息
from: https://www.jianshu.com/p/304ba7e9db29
//
// H264ParseSPS.h
//
// Created by lzj<lizhijian_21@163.com> on 2018/7/6.
// Copyright © 2018年 LZJ. All rights reserved.
//
#ifndef H264ParseSPS_h
#define H264ParseSPS_h
#ifdef __cplusplus
extern "C"
{
#endif
#include <stdio.h>
typedef struct
{
unsigned int profile_idc;
unsigned int level_idc;
unsigned int width;
unsigned int height;
unsigned int fps; //SPS中可能不包含FPS信息
} sps_info_struct;
/**
解析SPS数据信息
@param data SPS数据内容，需要Nal类型为0x7数据的开始(比如：67 42 00 28 ab 40 22 01 e3 cb cd c0 80 80 a9 02)
@param dataSize SPS数据的长度
@param info SPS解析之后的信息数据结构体
@return success:1，fail:0
*/
int h264_parse_sps(const unsigned char *data, unsigned int dataSize, sps_info_struct *info);
#ifdef __cplusplus
}
#endif
#endif /* H264ParseSPS_h */
//
// H264ParseSPS.c
//
// Created by lzj<lizhijian_21@163.com> on 2018/7/6.
// Copyright © 2018年 LZJ. All rights reserved.
//
// See https://www.itu.int/rec/T-REC-H.264-201610-S
//
#include "H264ParseSPS.h"
#include <string.h>
#include <stdlib.h>
#include <math.h>
typedef unsigned char BYTE;
typedef int INT;
typedef unsigned int UINT;
typedef struct
{
const BYTE *data; //sps数据
UINT size; //sps数据大小
UINT index; //当前计算位所在的位置标记
} sps_bit_stream;
/**
移除H264的NAL防竞争码(0x03)
@param data sps数据
@param dataSize sps数据大小
*/
static void del_emulation_prevention(BYTE *data, UINT *dataSize)
{
UINT dataSizeTemp = *dataSize;
for (UINT i=0, j=0; i<(dataSizeTemp-2); i++) {
int val = (data[i]^0x0) + (data[i+1]^0x0) + (data[i+2]^0x3); //检测是否是竞争码
if (val == 0) {
for (j=i+2; j<dataSizeTemp-1; j++) { //移除竞争码
data[j] = data[j+1];
}
(*dataSize)--; //data size 减1
}
}
}
static void sps_bs_init(sps_bit_stream *bs, const BYTE *data, UINT size)
{
if (bs) {
bs->data = data;
bs->size = size;
bs->index = 0;
}
}
/**
是否已经到数据流最后
@param bs sps_bit_stream数据
@return 1：yes，0：no
*/
static INT eof(sps_bit_stream *bs)
{
return (bs->index >= bs->size * 8); //位偏移已经超出数据
}
/**
读取从起始位开始的BitCount个位所表示的值
@param bs sps_bit_stream数据
@param bitCount bit位个数(从低到高)
@return value
*/
static UINT u(sps_bit_stream *bs, BYTE bitCount)
{
UINT val = 0;
for (BYTE i=0; i<bitCount; i++) {
val <<= 1;
if (eof(bs)) {
val = 0;
break;
} else if (bs->data[bs->index / 8] & (0x80 >> (bs->index % 8))) { //计算index所在的位是否为1
val |= 1;
}
bs->index++; //递增当前起始位(表示该位已经被计算，在后面的计算过程中不需要再次去计算所在的起始位索引，缺点：后面每个bit位都需要去位移)
}
return val;
}
/**
读取无符号哥伦布编码值(UE)
#2^LeadingZeroBits - 1 + (xxx)
@param bs sps_bit_stream数据
@return value
*/
static UINT ue(sps_bit_stream *bs)
{
UINT zeroNum = 0;
while (u(bs, 1) == 0 && !eof(bs) && zeroNum < 32) {
zeroNum ++;
}
return (UINT)((1 << zeroNum) - 1 + u(bs, zeroNum));
}
/**
读取有符号哥伦布编码值(SE)
#(-1)^(k+1) * Ceil(k/2)
@param bs sps_bit_stream数据
@return value
*/
INT se(sps_bit_stream *bs)
{
INT ueVal = (INT)ue(bs);
double k = ueVal;
INT seVal = (INT)ceil(k / 2); //ceil:返回大于或者等于指定表达式的最小整数
if (ueVal % 2 == 0) { //偶数取反，即(-1)^(k+1)
seVal = -seVal;
}
return seVal;
}
/**
视频可用性信息(Video usability information)解析
@param bs sps_bit_stream数据
@param info sps解析之后的信息数据及结构体
@see E.1.1 VUI parameters syntax
*/
void vui_para_parse(sps_bit_stream *bs, sps_info_struct *info)
{
UINT aspect_ratio_info_present_flag = u(bs, 1);
if (aspect_ratio_info_present_flag) {
UINT aspect_ratio_idc = u(bs, 8);
if (aspect_ratio_idc == 255) { //Extended_SAR
u(bs, 16); //sar_width
u(bs, 16); //sar_height
}
}
UINT overscan_info_present_flag = u(bs, 1);
if (overscan_info_present_flag) {
u(bs, 1); //overscan_appropriate_flag
}
UINT video_signal_type_present_flag = u(bs, 1);
if (video_signal_type_present_flag) {
u(bs, 3); //video_format
u(bs, 1); //video_full_range_flag
UINT colour_description_present_flag = u(bs, 1);
if (colour_description_present_flag) {
u(bs, 8); //colour_primaries
u(bs, 8); //transfer_characteristics
u(bs, 8); //matrix_coefficients
}
}
UINT chroma_loc_info_present_flag = u(bs, 1);
if (chroma_loc_info_present_flag) {
ue(bs); //chroma_sample_loc_type_top_field
ue(bs); //chroma_sample_loc_type_bottom_field
}
UINT timing_info_present_flag = u(bs, 1);
if (timing_info_present_flag) {
UINT num_units_in_tick = u(bs, 32);
UINT time_scale = u(bs, 32);
UINT fixed_frame_rate_flag = u(bs, 1);
info->fps = (UINT)((float)time_scale / (float)num_units_in_tick);
if (fixed_frame_rate_flag) {
info->fps = info->fps/2;
}
}
UINT nal_hrd_parameters_present_flag = u(bs, 1);
if (nal_hrd_parameters_present_flag) {
//hrd_parameters() //see E.1.2 HRD parameters syntax
}
//后面代码需要hrd_parameters()函数接口实现才有用
UINT vcl_hrd_parameters_present_flag = u(bs, 1);
if (vcl_hrd_parameters_present_flag) {
//hrd_parameters()
}
if (nal_hrd_parameters_present_flag || vcl_hrd_parameters_present_flag) {
u(bs, 1); //low_delay_hrd_flag
}
u(bs, 1); //pic_struct_present_flag
UINT bitstream_restriction_flag = u(bs, 1);
if (bitstream_restriction_flag) {
u(bs, 1); //motion_vectors_over_pic_boundaries_flag
ue(bs); //max_bytes_per_pic_denom
ue(bs); //max_bits_per_mb_denom
ue(bs); //log2_max_mv_length_horizontal
ue(bs); //log2_max_mv_length_vertical
ue(bs); //max_num_reorder_frames
ue(bs); //max_dec_frame_buffering
}
}
//See 7.3.1 NAL unit syntax
//See 7.3.2.1.1 Sequence parameter set data syntax
INT h264_parse_sps(const BYTE *data, UINT dataSize, sps_info_struct *info)
{
if (!data || dataSize <= 0 || !info) return 0;
INT ret = 0;
BYTE *dataBuf = malloc(dataSize);
memcpy(dataBuf, data, dataSize); //重新拷贝一份数据，防止移除竞争码时对原数据造成影响
del_emulation_prevention(dataBuf, &dataSize);
sps_bit_stream bs = {0};
sps_bs_init(&bs, dataBuf, dataSize); //初始化SPS数据流结构体
u(&bs, 1); //forbidden_zero_bit
u(&bs, 2); //nal_ref_idc
UINT nal_unit_type = u(&bs, 5);
if (nal_unit_type == 0x7) { //Nal SPS Flag
info->profile_idc = u(&bs, 8);
u(&bs, 1); //constraint_set0_flag
u(&bs, 1); //constraint_set1_flag
u(&bs, 1); //constraint_set2_flag
u(&bs, 1); //constraint_set3_flag
u(&bs, 1); //constraint_set4_flag
u(&bs, 1); //constraint_set4_flag
u(&bs, 2); //reserved_zero_2bits
info->level_idc = u(&bs, 8);
ue(&bs); //seq_parameter_set_id
UINT chroma_format_idc = 1; //摄像机出图大部分格式是4:2:0
if (info->profile_idc == 100 || info->profile_idc == 110 || info->profile_idc == 122 ||
info->profile_idc == 244 || info->profile_idc == 44 || info->profile_idc == 83 ||
info->profile_idc == 86 || info->profile_idc == 118 || info->profile_idc == 128 ||
info->profile_idc == 138 || info->profile_idc == 139 || info->profile_idc == 134 || info->profile_idc == 135) {
chroma_format_idc = ue(&bs);
if (chroma_format_idc == 3) {
u(&bs, 1); //separate_colour_plane_flag
}
ue(&bs); //bit_depth_luma_minus8
ue(&bs); //bit_depth_chroma_minus8
u(&bs, 1); //qpprime_y_zero_transform_bypass_flag
UINT seq_scaling_matrix_present_flag = u(&bs, 1);
if (seq_scaling_matrix_present_flag) {
UINT seq_scaling_list_present_flag[8] = {0};
for (INT i=0; i<((chroma_format_idc != 3)?8:12); i++) {
seq_scaling_list_present_flag[i] = u(&bs, 1);
if (seq_scaling_list_present_flag[i]) {
if (i < 6) { //scaling_list(ScalingList4x4[i], 16, UseDefaultScalingMatrix4x4Flag[I])
} else { //scaling_list(ScalingList8x8[i − 6], 64, UseDefaultScalingMatrix8x8Flag[i − 6] )
}
}
}
}
}
ue(&bs); //log2_max_frame_num_minus4
UINT pic_order_cnt_type = ue(&bs);
if (pic_order_cnt_type == 0) {
ue(&bs); //log2_max_pic_order_cnt_lsb_minus4
} else if (pic_order_cnt_type == 1) {
u(&bs, 1); //delta_pic_order_always_zero_flag
se(&bs); //offset_for_non_ref_pic
se(&bs); //offset_for_top_to_bottom_field
UINT num_ref_frames_in_pic_order_cnt_cycle = ue(&bs);
INT *offset_for_ref_frame = (INT *)malloc((UINT)num_ref_frames_in_pic_order_cnt_cycle * sizeof(INT));
for (INT i = 0; i<num_ref_frames_in_pic_order_cnt_cycle; i++) {
offset_for_ref_frame[i] = se(&bs);
}
free(offset_for_ref_frame);
}
ue(&bs); //max_num_ref_frames
u(&bs, 1); //gaps_in_frame_num_value_allowed_flag
UINT pic_width_in_mbs_minus1 = ue(&bs); //第36位开始
UINT pic_height_in_map_units_minus1 = ue(&bs); //47
UINT frame_mbs_only_flag = u(&bs, 1);
info->width = (INT)(pic_width_in_mbs_minus1 + 1) * 16;
info->height = (INT)(2 - frame_mbs_only_flag) * (pic_height_in_map_units_minus1 + 1) * 16;
if (!frame_mbs_only_flag) {
u(&bs, 1); //mb_adaptive_frame_field_flag
}
u(&bs, 1); //direct_8x8_inference_flag
UINT frame_cropping_flag = u(&bs, 1);
if (frame_cropping_flag) {
UINT frame_crop_left_offset = ue(&bs);
UINT frame_crop_right_offset = ue(&bs);
UINT frame_crop_top_offset = ue(&bs);
UINT frame_crop_bottom_offset= ue(&bs);
//See 6.2 Source, decoded, and output picture formats
INT crop_unit_x = 1;
INT crop_unit_y = 2 - frame_mbs_only_flag; //monochrome or 4:4:4
if (chroma_format_idc == 1) { //4:2:0
crop_unit_x = 2;
crop_unit_y = 2 * (2 - frame_mbs_only_flag);
} else if (chroma_format_idc == 2) { //4:2:2
crop_unit_x = 2;
crop_unit_y = 2 - frame_mbs_only_flag;
}
info->width -= crop_unit_x * (frame_crop_left_offset + frame_crop_right_offset);
info->height -= crop_unit_y * (frame_crop_top_offset + frame_crop_bottom_offset);
}
UINT vui_parameters_present_flag = u(&bs, 1);
if (vui_parameters_present_flag) {
vui_para_parse(&bs, info);
}
ret = 1;
}
free(dataBuf);
return ret;
}