h264 sps解析，提取宽高
1、sps 数据结构
1）、从Bit流中取出句法元素的方法。
|编号 | 语法 |说明|
1 ae(e) CABAC
2 b(8) 读进连续的8个Bit
3 ce(v) CAVLC
4 f(n) 读进连续的n个Bit
5 i(n)/i(v) 读进连续的若干Bit，并把它们解释为有符号整数
6 me(v) 映射指数Golomb熵编码
7 se(v) 有符号指数Golomb熵编码
8 te(v) 截断指数Golomb熵编码
9 u(n)/u(v) 读进连续的若干Bit，并把它们解释为无符号整数
10 ue(v) 无符号指数Golomb熵编码
主要是同过bitstream.h 进行处理的 代码如下：
# ifdef NOCACHE
typedef struct {
const uint8_t *data; //存放除了sps数据
int count; /* in bits */
int index; /* in bits */
} br_state;
#define BR_INIT(data,bytes) {(data), 8*(bytes), 0}
#define BR_EOF(br) ((br)->index >= (br)->count)
static inline void br_init(br_state *br, const uint8_t *data, int bytes)
{
br->data = data;
br->count = 8*bytes;
br->index = 0;
}
static inline int br_get_bit(br_state *br)
{
if(br->index >= br->count)
return 1; /* -> no infinite colomb's ... */
int r = (br->data[br->index>>3] >> (7 - (br->index&7))) & 1;
br->index++;
return r;
}
static inline uint32_t br_get_bits(br_state *br, uint32_t n)
{
uint32_t r = 0;
while(n--)
r = r | (br_get_bit(br) << n);
return r;
}
#define br_skip_bit(br) br_skip_bits(br,1)
static inline void br_skip_bits(br_state *br, int n)
{
br->index += n;
}
# else /* NOCACHE */
typedef struct {
uint8_t *data;
uint8_t *data_end;
uint32_t cache;
uint32_t cache_bits;
} br_state;
#define BR_INIT(data,bytes) {(data), (data)+(bytes), 0, 0}
static inline void br_init(br_state *br, const uint8_t *data, int bytes)
{
br->data = data;
br->data_end = data + bytes;
br->cache = 0;
br->cache_bits = 0;
}
#define BR_GET_BYTE(br) \
(br->data < br->data_end ? *br->data++ : 0xff)
#define BR_EOF(br) ((br)->data >= (br)->data_end)
static inline uint32_t br_get_bits(br_state *br, uint32_t n)
{
if(n > 24)
return (br_get_bits(br, 16) << 16) | br_get_bits(br, n-16);
while (br->cache_bits < 24) {
br->cache = (br->cache<<8) | BR_GET_BYTE(br);
br->cache_bits += 8;
}
br->cache_bits -= n;
return (br->cache >> br->cache_bits) & ((1<1);
}
static inline int br_get_bit(br_state *br)
{
if(!br->cache_bits) {
br->cache = BR_GET_BYTE(br);
br->cache_bits = 7;
} else {
br->cache_bits--;
}
return (br->cache >> br->cache_bits) & 1;
}
static inline void br_skip_bit(br_state *br)
{
if(!br->cache_bits) {
br->cache = BR_GET_BYTE(br);
br->cache_bits = 7;
} else {
br->cache_bits--;
}
}
static inline void br_skip_bits(br_state *br, int n)
{
if(br->cache_bits >= n) {
br->cache_bits -= n;
} else {
/* drop cached bits */
n -= br->cache_bits;
/* drop full bytes */
br->data += (n >> 3);
n &= 7;
/* update cache */
if(n) {
br->cache = BR_GET_BYTE(br);
br->cache_bits = 8 - n;
} else {
br->cache_bits = 0;
}
}
}
# endif /* NOCACHE */
#define br_get_u8(br) br_get_bits(br, 8)
#define br_get_u16(br) ((br_get_bits(br, 8)<<8) | br_get_bits(br, 8))
static inline uint32_t br_get_ue_golomb(br_state *br)
{
int n = 0;
while (!br_get_bit(br) && n < 32)
n++;
return n ? ((1<1) + br_get_bits(br, n) : 0;
}
#pragma warning(disable: 4146)
static inline int32_t br_get_se_golomb(br_state *br)
{
uint32_t r = br_get_ue_golomb(br) + 1;
return (r&1) ? -(r>>1) : (r>>1);
}
static inline void br_skip_golomb(br_state *br)
{
int n = 0;
while (!br_get_bit(br) && n < 32)
n++;
br_skip_bits(br, n);
}
#define br_skip_ue_golomb(br) br_skip_golomb(br)
#define br_skip_se_golomb(br) br_skip_golomb(br) 2、nal 语法
自己百度或google。这里就不介绍了，下面具体说下sps结构体里面的字段
3、sps
详细信息可以参考链接sps详解介绍
4、代码实现
#ifndef __SPSparse__SPS__
#define __SPSparse__SPS__
#include #include "SPS.h"
#include