H.264（H264）解码SPS获取分辨率和帧率

怼烎@ 2022-06-12 03:49 474阅读 0赞

**\[cpp\]**  [view plain][]   [copy][view plain]

1.  \#include <stdio.h>  
2.  \#include <stdint.h>  
3.  \#include <string.h>  
4.  \#include <math.h>  
5.    
6.  **typedef**  unsigned **int** **UINT**;  
7.  **typedef**  unsigned **char** **BYTE**;  
8.  **typedef**  unsigned **long** **DWORD**;  
9.    
10. **UINT** Ue(**BYTE** \*pBuff, **UINT** nLen, **UINT** &nStartBit)  
11. \{  
12.     //计算0bit的个数  
13.     **UINT** nZeroNum = 0;  
14.     **while** (nStartBit < nLen \* 8)  
15.     \{  
16.         **if** (pBuff\[nStartBit / 8\] & (0x80 >> (nStartBit % 8))) //&:按位与，%取余  
17.         \{  
18.             **break**;  
19.         \}  
20.         nZeroNum++;  
21.         nStartBit++;  
22.     \}  
23.     nStartBit ++;  
24.   
25.   
26.     //计算结果  
27.     **DWORD** dwRet = 0;  
28.     **for** (**UINT** i=0; i<nZeroNum; i++)  
29.     \{  
30.         dwRet <<= 1;  
31.         **if** (pBuff\[nStartBit / 8\] & (0x80 >> (nStartBit % 8)))  
32.         \{  
33.             dwRet += 1;  
34.         \}  
35.         nStartBit++;  
36.     \}  
37.     **return** (1 << nZeroNum) - 1 + dwRet;  
38. \}  
39.   
40.   
41. **int** Se(**BYTE** \*pBuff, **UINT** nLen, **UINT** &nStartBit)  
42. \{  
43.     **int** UeVal=Ue(pBuff,nLen,nStartBit);  
44.     **double** k=UeVal;  
45.     **int** nValue=ceil(k/2);//ceil函数：ceil函数的作用是求不小于给定实数的最小整数。ceil(2)=ceil(1.2)=cei(1.5)=2.00  
46.     **if** (UeVal % 2==0)  
47.         nValue=-nValue;  
48.     **return** nValue;  
49. \}  
50.   
51.   
52. **DWORD** u(**UINT** BitCount,**BYTE** \* buf,**UINT** &nStartBit)  
53. \{  
54.     **DWORD** dwRet = 0;  
55.     **for** (**UINT** i=0; i<BitCount; i++)  
56.     \{  
57.         dwRet <<= 1;  
58.         **if** (buf\[nStartBit / 8\] & (0x80 >> (nStartBit % 8)))  
59.         \{  
60.             dwRet += 1;  
61.         \}  
62.         nStartBit++;  
63.     \}  
64.     **return** dwRet;  
65. \}  
66.   
67. /\*\* 
68.  \* H264的NAL起始码防竞争机制 
69.  \* 
70.  \* @param buf SPS数据内容 
71.  \* 
72.  \* @无返回值 
73.  \*/  
74. **void** de\_emulation\_prevention(**BYTE**\* buf,unsigned **int**\* buf\_size)  
75. \{  
76.     **int** i=0,j=0;  
77.     **BYTE**\* tmp\_ptr=NULL;  
78.     unsigned **int** tmp\_buf\_size=0;  
79.     **int** val=0;  
80.   
81.     tmp\_ptr=buf;  
82.     tmp\_buf\_size=\*buf\_size;  
83.     **for**(i=0;i<(tmp\_buf\_size-2);i++)  
84.     \{  
85.         //check for 0x000003  
86.         val=(tmp\_ptr\[i\]^0x00) +(tmp\_ptr\[i+1\]^0x00)+(tmp\_ptr\[i+2\]^0x03);  
87.         **if**(val==0)  
88.         \{  
89.             //kick out 0x03  
90.             **for**(j=i+2;j<tmp\_buf\_size-1;j++)  
91.                 tmp\_ptr\[j\]=tmp\_ptr\[j+1\];  
92.   
93.             //and so we should devrease bufsize  
94.             (\*buf\_size)--;  
95.         \}  
96.     \}  
97. \}  
98.   
99. /\*\* 
100.  \* 解码SPS,获取视频图像宽、高和帧率信息 
101.  \* 
102.  \* @param buf SPS数据内容 
103.  \* @param nLen SPS数据的长度 
104.  \* @param width 图像宽度 
105.  \* @param height 图像高度 
106.  
107.  \* @成功则返回true , 失败则返回false 
108.  \*/  
109. **bool** h264\_decode\_sps(**BYTE** \* buf,unsigned **int** nLen,**int** &width,**int** &height,**int** &fps)  
110. \{  
111.     **UINT** StartBit=0;  
112.     fps=0;  
113.     de\_emulation\_prevention(buf,&nLen);  
114.   
115.     **int** forbidden\_zero\_bit=u(1,buf,StartBit);  
116.     **int** nal\_ref\_idc=u(2,buf,StartBit);  
117.     **int** nal\_unit\_type=u(5,buf,StartBit);  
118.     **if**(nal\_unit\_type==7)  
119.     \{  
120.         **int** profile\_idc=u(8,buf,StartBit);  
121.         **int** constraint\_set0\_flag=u(1,buf,StartBit);//(buf\[1\] & 0x80)>>7;  
122.         **int** constraint\_set1\_flag=u(1,buf,StartBit);//(buf\[1\] & 0x40)>>6;  
123.         **int** constraint\_set2\_flag=u(1,buf,StartBit);//(buf\[1\] & 0x20)>>5;  
124.         **int** constraint\_set3\_flag=u(1,buf,StartBit);//(buf\[1\] & 0x10)>>4;  
125.         **int** reserved\_zero\_4bits=u(4,buf,StartBit);  
126.         **int** level\_idc=u(8,buf,StartBit);  
127.   
128.         **int** seq\_parameter\_set\_id=Ue(buf,nLen,StartBit);  
129.   
130.         **if**( profile\_idc == 100 || profile\_idc == 110 ||  
131.             profile\_idc == 122 || profile\_idc == 144 )  
132.         \{  
133.             **int** chroma\_format\_idc=Ue(buf,nLen,StartBit);  
134.             **if**( chroma\_format\_idc == 3 )  
135.                 **int** residual\_colour\_transform\_flag=u(1,buf,StartBit);  
136.             **int** bit\_depth\_luma\_minus8=Ue(buf,nLen,StartBit);  
137.             **int** bit\_depth\_chroma\_minus8=Ue(buf,nLen,StartBit);  
138.             **int** qpprime\_y\_zero\_transform\_bypass\_flag=u(1,buf,StartBit);  
139.             **int** seq\_scaling\_matrix\_present\_flag=u(1,buf,StartBit);  
140.   
141.             **int** seq\_scaling\_list\_present\_flag\[8\];  
142.             **if**( seq\_scaling\_matrix\_present\_flag )  
143.             \{  
144.                 **for**( **int** i = 0; i < 8; i++ ) \{  
145.                     seq\_scaling\_list\_present\_flag\[i\]=u(1,buf,StartBit);  
146.                 \}  
147.             \}  
148.         \}  
149.         **int** log2\_max\_frame\_num\_minus4=Ue(buf,nLen,StartBit);  
150.         **int** pic\_order\_cnt\_type=Ue(buf,nLen,StartBit);  
151.         **if**( pic\_order\_cnt\_type == 0 )  
152.             **int** log2\_max\_pic\_order\_cnt\_lsb\_minus4=Ue(buf,nLen,StartBit);  
153.         **else** **if**( pic\_order\_cnt\_type == 1 )  
154.         \{  
155.             **int** delta\_pic\_order\_always\_zero\_flag=u(1,buf,StartBit);  
156.             **int** offset\_for\_non\_ref\_pic=Se(buf,nLen,StartBit);  
157.             **int** offset\_for\_top\_to\_bottom\_field=Se(buf,nLen,StartBit);  
158.             **int** num\_ref\_frames\_in\_pic\_order\_cnt\_cycle=Ue(buf,nLen,StartBit);  
159.   
160.             **int** \*offset\_for\_ref\_frame=**new** **int**\[num\_ref\_frames\_in\_pic\_order\_cnt\_cycle\];  
161.             **for**( **int** i = 0; i < num\_ref\_frames\_in\_pic\_order\_cnt\_cycle; i++ )  
162.                 offset\_for\_ref\_frame\[i\]=Se(buf,nLen,StartBit);  
163.             **delete** \[\] offset\_for\_ref\_frame;  
164.         \}  
165.         **int** num\_ref\_frames=Ue(buf,nLen,StartBit);  
166.         **int** gaps\_in\_frame\_num\_value\_allowed\_flag=u(1,buf,StartBit);  
167.         **int** pic\_width\_in\_mbs\_minus1=Ue(buf,nLen,StartBit);  
168.         **int** pic\_height\_in\_map\_units\_minus1=Ue(buf,nLen,StartBit);  
169.   
170.         width=(pic\_width\_in\_mbs\_minus1+1)\*16;  
171.         height=(pic\_height\_in\_map\_units\_minus1+1)\*16;  
172.   
173.         **int** frame\_mbs\_only\_flag=u(1,buf,StartBit);  
174.         **if**(!frame\_mbs\_only\_flag)  
175.             **int** mb\_adaptive\_frame\_field\_flag=u(1,buf,StartBit);  
176.   
177.         **int** direct\_8x8\_inference\_flag=u(1,buf,StartBit);  
178.         **int** frame\_cropping\_flag=u(1,buf,StartBit);  
179.         **if**(frame\_cropping\_flag)  
180.         \{  
181.             **int** frame\_crop\_left\_offset=Ue(buf,nLen,StartBit);  
182.             **int** frame\_crop\_right\_offset=Ue(buf,nLen,StartBit);  
183.             **int** frame\_crop\_top\_offset=Ue(buf,nLen,StartBit);  
184.             **int** frame\_crop\_bottom\_offset=Ue(buf,nLen,StartBit);  
185.         \}  
186.         **int** vui\_parameter\_present\_flag=u(1,buf,StartBit);  
187.         **if**(vui\_parameter\_present\_flag)  
188.         \{  
189.             **int** aspect\_ratio\_info\_present\_flag=u(1,buf,StartBit);  
190.             **if**(aspect\_ratio\_info\_present\_flag)  
191.             \{  
192.                 **int** aspect\_ratio\_idc=u(8,buf,StartBit);  
193.                 **if**(aspect\_ratio\_idc==255)  
194.                 \{  
195.                     **int** sar\_width=u(16,buf,StartBit);  
196.                     **int** sar\_height=u(16,buf,StartBit);  
197.                 \}  
198.             \}  
199.             **int** overscan\_info\_present\_flag=u(1,buf,StartBit);  
200.             **if**(overscan\_info\_present\_flag)  
201.                 **int** overscan\_appropriate\_flagu=u(1,buf,StartBit);  
202.             **int** video\_signal\_type\_present\_flag=u(1,buf,StartBit);  
203.             **if**(video\_signal\_type\_present\_flag)  
204.             \{  
205.                 **int** video\_format=u(3,buf,StartBit);  
206.                 **int** video\_full\_range\_flag=u(1,buf,StartBit);  
207.                 **int** colour\_description\_present\_flag=u(1,buf,StartBit);  
208.                 **if**(colour\_description\_present\_flag)  
209.                 \{  
210.                     **int** colour\_primaries=u(8,buf,StartBit);  
211.                     **int** transfer\_characteristics=u(8,buf,StartBit);  
212.                     **int** matrix\_coefficients=u(8,buf,StartBit);  
213.                 \}  
214.             \}  
215.             **int** chroma\_loc\_info\_present\_flag=u(1,buf,StartBit);  
216.             **if**(chroma\_loc\_info\_present\_flag)  
217.             \{  
218.                 **int** chroma\_sample\_loc\_type\_top\_field=Ue(buf,nLen,StartBit);  
219.                 **int** chroma\_sample\_loc\_type\_bottom\_field=Ue(buf,nLen,StartBit);  
220.             \}  
221.             **int** timing\_info\_present\_flag=u(1,buf,StartBit);  
222.   
223.             **if**(timing\_info\_present\_flag)  
224.             \{  
225.                 **int** num\_units\_in\_tick=u(32,buf,StartBit);  
226.                 **int** time\_scale=u(32,buf,StartBit);  
227.                 fps=time\_scale/num\_units\_in\_tick;  
228.                 **int** fixed\_frame\_rate\_flag=u(1,buf,StartBit);  
229.                 **if**(fixed\_frame\_rate\_flag)  
230.                 \{  
231.                     fps=fps/2;  
232.                 \}  
233.             \}  
234.         \}  
235.         **return** **true**;  
236.     \}  
237.     **else**  
238.         **return** **false**;  
239. \}

timing\_info\_present\_flag等于1表示num\_units\_in\_tick，time\_scale和fixed\_frame\_rate\_flag在比特流中存在。

timing\_info\_present\_flag等于0表示num\_units\_in\_tick，time\_scale和fixed\_frame\_rate\_flag在比特流中不存在。

因此，当timing\_info\_present\_flag等于0时，无法得到码率，bool h264\_decode\_sps(BYTE \* buf,unsigned int nLen,int &width,int &height,int &fps)参数fps返回值为0，可据此设置一个默认帧率。

参考链接：[http://blog.csdn.net/qq\_27727131/article/details/51799663][http_blog.csdn.net_qq_27727131_article_details_51799663]

[![20161108162227570][]][20161108162227570 1]

[view plain]: http://blog.csdn.net/caoshangpa/article/details/53083410#
[http_blog.csdn.net_qq_27727131_article_details_51799663]: http://blog.csdn.net/qq_27727131/article/details/51799663
[20161108162227570]: /images/20220612/51f26cb0cae24c409330e81053cbc30b.png
[20161108162227570 1]: http://blog.csdn.net/caoshangpa