从零开始写一个RTSP服务器系列

★我的开源项目-RtspServer

从零开始写一个RTSP服务器（一）RTSP协议讲解

从零开始写一个RTSP服务器（二）RTSP协议的实现

从零开始写一个RTSP服务器（三）RTP传输H.264

从零开始写一个RTSP服务器（四）一个传输H.264的RTSP服务器

从零开始写一个RTSP服务器（五）RTP传输AAC

从零开始写一个RTSP服务器（六）一个传输AAC的RTSP服务器

从零开始写一个RTSP服务器（七）多播传输RTP包

从零开始写一个RTSP服务器（八）一个多播的RTSP服务器

从零开始写一个RTSP服务器（九）一个RTP OVER RTSP/TCP的RTSP服务器

从零开始写一个RTSP服务器（三）RTP传输H.264

文章目录

• 从零开始写一个RTSP服务器（三）RTP传输H.264
• • 一、RTP封装
  • • 1.1 RTP数据结构
    • 1.2 源码
    • • rtp.h
      • rtp.c
  • 二、H.264的RTP打包
  • • 2.1 H.264格式
    • 2.2 H.264的RTP打包方式
    • • 单NALU打包
      • 分片打包
    • 2.3 H.264 RTP包的时间戳计算
    • 2.4 源码
    • • rtp_h264.c
  • 三、H.264 RTP打包的sdp描述
  • 四、测试

一、RTP封装

1.1 RTP数据结构

RTP包格式前面已经比较详细的介绍过，参考从零开始写一个RTSP服务器（一）不一样的RTSP协议讲解

看一张RTP头的格式图回忆一下

每个RTP包都包含这样一个RTP头部和RTP数据，为了方便，我将这个头部封装成一个结构体，还有发送包封装成一个函数，下面来看一看

• RTP头结构体

/*
* 作者：_JT_
* 博客：https://blog.csdn.net/weixin_42462202
*/

struct RtpHeader
{
/* byte 0 */
uint8_t csrcLen:4;
uint8_t extension:1;
uint8_t padding:1;
uint8_t version:2;

 <span class="token comment">/* byte 1 */</span>
 uint8_t payloadType<span class="token punctuation">:</span><span class="token number">7</span><span class="token punctuation">;</span>
 uint8_t marker<span class="token punctuation">:</span><span class="token number">1</span><span class="token punctuation">;</span>
 
 <span class="token comment">/* bytes 2,3 */</span>
 uint16_t seq<span class="token punctuation">;</span>
 
 <span class="token comment">/* bytes 4-7 */</span>
 uint32_t timestamp<span class="token punctuation">;</span>
 
 <span class="token comment">/* bytes 8-11 */</span>
 uint32_t ssrc<span class="token punctuation">;</span>

};

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其中的:n是一种位表示法，这个结构体跟RTP的头部一一对应

• RTP的发包函数

  RTP包

  struct RtpPacket
  {
      struct RtpHeader rtpHeader;
      uint8_t payload[0];
  };
  
     
  
     
  1
  2
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  5

  这是我封装的一个RTP包，包含一个RTP头部和RTP载荷，uint8_t payload[0]并不占用空间，它表示rtp头部接下来紧跟着的地址

  RTP的发包函数

  /*
   * 函数功能：发送RTP包
   * 参数 socket：表示本机的udp套接字
   * 参数 ip：表示目的ip地址
   * 参数 port：表示目的的端口号
   * 参数 rtpPacket：表示rtp包
   * 参数 dataSize：表示rtp包中载荷的大小
   * 放回值：发送字节数
   */
  int rtpSendPacket(int socket, char* ip, int16_t port, struct RtpPacket* rtpPacket, uint32_t dataSize)
  {
      struct sockaddr_in addr;
      int ret;
  addr<span class="token punctuation">.</span>sin_family <span class="token operator">=</span> AF_INET<span class="token punctuation">;</span>
  addr<span class="token punctuation">.</span>sin_port <span class="token operator">=</span> <span class="token function">htons</span><span class="token punctuation">(</span>port<span class="token punctuation">)</span><span class="token punctuation">;</span>
  addr<span class="token punctuation">.</span>sin_addr<span class="token punctuation">.</span>s_addr <span class="token operator">=</span> <span class="token function">inet_addr</span><span class="token punctuation">(</span>ip<span class="token punctuation">)</span><span class="token punctuation">;</span>
  
  rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq <span class="token operator">=</span> <span class="token function">htons</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token punctuation">)</span><span class="token punctuation">;</span>
  rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp <span class="token operator">=</span> <span class="token function">htonl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp<span class="token punctuation">)</span><span class="token punctuation">;</span>
  rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc <span class="token operator">=</span> <span class="token function">htonl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc<span class="token punctuation">)</span><span class="token punctuation">;</span>
  
  ret <span class="token operator">=</span> <span class="token function">sendto</span><span class="token punctuation">(</span>socket<span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token keyword">void</span><span class="token operator">*</span><span class="token punctuation">)</span>rtpPacket<span class="token punctuation">,</span> dataSize<span class="token operator">+</span>RTP_HEADER_SIZE<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span>
                  <span class="token punctuation">(</span><span class="token keyword">struct</span> sockaddr<span class="token operator">*</span><span class="token punctuation">)</span><span class="token operator">&amp;</span>addr<span class="token punctuation">,</span> <span class="token keyword">sizeof</span><span class="token punctuation">(</span>addr<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  
  rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq <span class="token operator">=</span> <span class="token function">ntohs</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token punctuation">)</span><span class="token punctuation">;</span>
  rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp <span class="token operator">=</span> <span class="token function">ntohl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp<span class="token punctuation">)</span><span class="token punctuation">;</span>
  rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc <span class="token operator">=</span> <span class="token function">ntohl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc<span class="token punctuation">)</span><span class="token punctuation">;</span>
  
  <span class="token keyword">return</span> ret<span class="token punctuation">;</span>
  
  

}

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仔细看这个函数你应该可以看懂

我们设置好一个包之后，就会调用这个函数发送指定目标

这个函数中多处使用htons等函数，是因为RTP是采用网络字节序（大端模式），所以要将主机字节字节序转换为网络字节序

下面给出源码，rtp.h和rtp.c，这两个文件在后面讲经常使用

1.2 源码

rtp.h

/*
 * 作者：_JT_
 * 博客：https://blog.csdn.net/weixin_42462202
 */

#ifndef RTP_H
#define RTP_H
#include <stdint.h>

#define RTP_VESION 2

#define RTP_PAYLOAD_TYPE_H264 96
#define RTP_PAYLOAD_TYPE_AAC 97

#define RTP_HEADER_SIZE 12
#define RTP_MAX_PKT_SIZE 1400

/*
*

• 0 1 2 3
• 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
• ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±+
• |V=2|P|X| CC |M| PT | sequence number |
• ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±+
• | timestamp |
• ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±+
• | synchronization source (SSRC) identifier |
• +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
• | contributing source (CSRC) identifiers |
• : … :
• ±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±+

/
struct RtpHeader
{
/ byte 0 */
uint8_t csrcLen:4;
uint8_t extension:1;
uint8_t padding:1;
uint8_t version:2;

<span class="token comment">/* byte 1 */</span>
uint8_t payloadType<span class="token punctuation">:</span><span class="token number">7</span><span class="token punctuation">;</span>
uint8_t marker<span class="token punctuation">:</span><span class="token number">1</span><span class="token punctuation">;</span>

<span class="token comment">/* bytes 2,3 */</span>
uint16_t seq<span class="token punctuation">;</span>

<span class="token comment">/* bytes 4-7 */</span>
uint32_t timestamp<span class="token punctuation">;</span>

<span class="token comment">/* bytes 8-11 */</span>
uint32_t ssrc<span class="token punctuation">;</span>

};

struct RtpPacket
{
struct RtpHeader rtpHeader;
uint8_t payload[0];
};

void rtpHeaderInit(struct RtpPacket rtpPacket, uint8_t csrcLen, uint8_t extension,
uint8_t padding, uint8_t version, uint8_t payloadType, uint8_t marker,
uint16_t seq, uint32_t timestamp, uint32_t ssrc);
int rtpSendPacket(int socket, char ip, int16_t port, struct RtpPacket* rtpPacket, uint32_t dataSize);

#endif //RTP_H

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rtp.c

/*
 * 作者：_JT_
 * 博客：https://blog.csdn.net/weixin_42462202
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include “rtp.h”

void rtpHeaderInit(struct RtpPacket* rtpPacket, uint8_t csrcLen, uint8_t extension,
uint8_t padding, uint8_t version, uint8_t payloadType, uint8_t marker,
uint16_t seq, uint32_t timestamp, uint32_t ssrc)
{
rtpPacket->rtpHeader.csrcLen = csrcLen;
rtpPacket->rtpHeader.extension = extension;
rtpPacket->rtpHeader.padding = padding;
rtpPacket->rtpHeader.version = version;
rtpPacket->rtpHeader.payloadType = payloadType;
rtpPacket->rtpHeader.marker = marker;
rtpPacket->rtpHeader.seq = seq;
rtpPacket->rtpHeader.timestamp = timestamp;
rtpPacket->rtpHeader.ssrc = ssrc;
}

int rtpSendPacket(int socket, char ip, int16_t port, struct RtpPacket rtpPacket, uint32_t dataSize)
{
struct sockaddr_in addr;
int ret;

addr<span class="token punctuation">.</span>sin_family <span class="token operator">=</span> AF_INET<span class="token punctuation">;</span>
addr<span class="token punctuation">.</span>sin_port <span class="token operator">=</span> <span class="token function">htons</span><span class="token punctuation">(</span>port<span class="token punctuation">)</span><span class="token punctuation">;</span>
addr<span class="token punctuation">.</span>sin_addr<span class="token punctuation">.</span>s_addr <span class="token operator">=</span> <span class="token function">inet_addr</span><span class="token punctuation">(</span>ip<span class="token punctuation">)</span><span class="token punctuation">;</span>

rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq <span class="token operator">=</span> <span class="token function">htons</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token punctuation">)</span><span class="token punctuation">;</span>
rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp <span class="token operator">=</span> <span class="token function">htonl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp<span class="token punctuation">)</span><span class="token punctuation">;</span>
rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc <span class="token operator">=</span> <span class="token function">htonl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc<span class="token punctuation">)</span><span class="token punctuation">;</span>

ret <span class="token operator">=</span> <span class="token function">sendto</span><span class="token punctuation">(</span>socket<span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token keyword">void</span><span class="token operator">*</span><span class="token punctuation">)</span>rtpPacket<span class="token punctuation">,</span> dataSize<span class="token operator">+</span>RTP_HEADER_SIZE<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span>
                <span class="token punctuation">(</span><span class="token keyword">struct</span> sockaddr<span class="token operator">*</span><span class="token punctuation">)</span><span class="token operator">&amp;</span>addr<span class="token punctuation">,</span> <span class="token keyword">sizeof</span><span class="token punctuation">(</span>addr<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq <span class="token operator">=</span> <span class="token function">ntohs</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token punctuation">)</span><span class="token punctuation">;</span>
rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp <span class="token operator">=</span> <span class="token function">ntohl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp<span class="token punctuation">)</span><span class="token punctuation">;</span>
rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc <span class="token operator">=</span> <span class="token function">ntohl</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>ssrc<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span> ret<span class="token punctuation">;</span>

}

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二、H.264的RTP打包

2.1 H.264格式

H.264由一个一个的NALU组成，每个NALU之间使用00 00 00 01或00 00 01分隔开

每个NALU的第一次字节都有特殊的含义，其内容如下

好，对于H.264格式了解这么多就够了，我们的目的是想从一个H.264的文件中将一个一个的NALU提取出来，然后封装成RTP包，下面介绍如何将NALU封装成RTP包

2.2 H.264的RTP打包方式

H.264可以由三种RTP打包方式

• 单NALU打包

  一个RTP包包含一个完整的NALU

• 聚合打包

  对于较小的NALU，一个RTP包可包含多个完整的NALU

• 分片打包

  对于较大的NALU，一个NALU可以分为多个RTP包发送

注意：这里要区分好概念，每一个RTP包都包含一个RTP头部和RTP荷载，这是固定的。而H.264发送数据可支持三种RTP打包方式

比较常用的是单NALU打包和分片打包，本文也只介绍这两种

单NALU打包

所谓单NALU打包就是将一整个NALU的数据放入RTP包的载荷中

这是最简单的一种方式，无需过多的讲解

分片打包

每个RTP包都有大小限制的，因为RTP一般都是使用UDP发送，UDP没有流量控制，所以要限制每一次发送的大小，所以如果一个NALU的太大，就需要分成多个RTP包发送，如何分成多个RTP包，下面来好好讲一讲

首先要明确，RTP包的格式是绝不会变的，永远多是RTP头+RTP载荷

RTP头部是固定的，那么只能在RTP载荷中去添加额外信息来说明这个RTP包是表示同一个NALU

如果是分片打包的话，那么在RTP载荷开始有两个字节的信息，然后再是NALU的内容

• 第一个字节位FU Indicator，其格式如下
  
  高三位：与NALU第一个字节的高三位相同

  Type：28，表示该RTP包一个分片，为什么是28？因为H.264的规范中定义的，此外还有许多其他Type，这里不详讲

• 第二个字节位FU Header，其格式如下

  

  S：标记该分片打包的第一个RTP包

  E：比较该分片打包的最后一个RTP包

  Type：NALU的Type

2.3 H.264 RTP包的时间戳计算

RTP包的时间戳起始值是随机的

RTP包的时间戳增量怎么计算？

假设时钟频率为90000，帧率为25

频率为90000表示一秒用90000点来表示

帧率为25，那么一帧就是1/25秒

所以一帧有90000*(1/25)=3600个点来表示

因此每一帧数据的时间增量为3600

2.4 源码

rtp_h264.c

这里给出rtp发送H.264的源码

/*
 * 作者：_JT_
 * 博客：https://blog.csdn.net/weixin_42462202
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#include “rtp.h”

#define H264_FILE_NAME “test.h264”
#define CLIENT_IP “127.0.0.1”
#define CLIENT_PORT 9832

#define FPS 25

static inline int startCode3(char* buf)
{
if(buf[0] 0 && buf[1] 0 && buf[2] == 1)
return 1;
else
return 0;
}

static inline int startCode4(char* buf)
{
if(buf[0] 0 && buf[1] 0 && buf[2] 0 && buf[3] 1)
return 1;
else
return 0;
}

static char findNextStartCode(char buf, int len)
{
int i;

<span class="token keyword">if</span><span class="token punctuation">(</span>len <span class="token operator">&lt;</span> <span class="token number">3</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>

<span class="token keyword">for</span><span class="token punctuation">(</span>i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> len<span class="token operator">-</span><span class="token number">3</span><span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
    <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">startCode3</span><span class="token punctuation">(</span>buf<span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token function">startCode4</span><span class="token punctuation">(</span>buf<span class="token punctuation">)</span><span class="token punctuation">)</span>
        <span class="token keyword">return</span> buf<span class="token punctuation">;</span>
    
    <span class="token operator">++</span>buf<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">startCode3</span><span class="token punctuation">(</span>buf<span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> buf<span class="token punctuation">;</span>

<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>

}

static int getFrameFromH264File(int fd, char frame, int size)
{
int rSize, frameSize;
char nextStartCode;

<span class="token keyword">if</span><span class="token punctuation">(</span>fd <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> fd<span class="token punctuation">;</span>

rSize <span class="token operator">=</span> <span class="token function">read</span><span class="token punctuation">(</span>fd<span class="token punctuation">,</span> frame<span class="token punctuation">,</span> size<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">startCode3</span><span class="token punctuation">(</span>frame<span class="token punctuation">)</span> <span class="token operator">&amp;&amp;</span> <span class="token operator">!</span><span class="token function">startCode4</span><span class="token punctuation">(</span>frame<span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>

nextStartCode <span class="token operator">=</span> <span class="token function">findNextStartCode</span><span class="token punctuation">(</span>frame<span class="token operator">+</span><span class="token number">3</span><span class="token punctuation">,</span> rSize<span class="token operator">-</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span>nextStartCode<span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
    <span class="token function">lseek</span><span class="token punctuation">(</span>fd<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token constant">SEEK_SET</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    frameSize <span class="token operator">=</span> rSize<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">else</span>
<span class="token punctuation">{<!-- --></span>
    frameSize <span class="token operator">=</span> <span class="token punctuation">(</span>nextStartCode<span class="token operator">-</span>frame<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">lseek</span><span class="token punctuation">(</span>fd<span class="token punctuation">,</span> frameSize<span class="token operator">-</span>rSize<span class="token punctuation">,</span> <span class="token constant">SEEK_CUR</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">return</span> frameSize<span class="token punctuation">;</span>

}

static int createUdpSocket()
{
int fd;
int on = 1;

fd <span class="token operator">=</span> <span class="token function">socket</span><span class="token punctuation">(</span>AF_INET<span class="token punctuation">,</span> SOCK_DGRAM<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>fd <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>

<span class="token function">setsockopt</span><span class="token punctuation">(</span>fd<span class="token punctuation">,</span> SOL_SOCKET<span class="token punctuation">,</span> SO_REUSEADDR<span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token keyword">const</span> <span class="token keyword">char</span><span class="token operator">*</span><span class="token punctuation">)</span><span class="token operator">&amp;</span>on<span class="token punctuation">,</span> <span class="token keyword">sizeof</span><span class="token punctuation">(</span>on<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span> fd<span class="token punctuation">;</span>

}

static int rtpSendH264Frame(int socket, char ip, int16_t port,
struct RtpPacket rtpPacket, uint8_t* frame, uint32_t frameSize)
{
uint8_t naluType; // nalu第一个字节
int sendBytes = 0;
int ret;

naluType <span class="token operator">=</span> frame<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>frameSize <span class="token operator">&lt;=</span> RTP_MAX_PKT_SIZE<span class="token punctuation">)</span> <span class="token comment">// nalu长度小于最大包场：单一NALU单元模式</span>
<span class="token punctuation">{<!-- --></span>
    <span class="token comment">/*
     *   0 1 2 3 4 5 6 7 8 9
     *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     *  |F|NRI|  Type   | a single NAL unit ... |
     *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     */</span>
    <span class="token function">memcpy</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">,</span> frame<span class="token punctuation">,</span> frameSize<span class="token punctuation">)</span><span class="token punctuation">;</span>
    ret <span class="token operator">=</span> <span class="token function">rtpSendPacket</span><span class="token punctuation">(</span>socket<span class="token punctuation">,</span> ip<span class="token punctuation">,</span> port<span class="token punctuation">,</span> rtpPacket<span class="token punctuation">,</span> frameSize<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>ret <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
        <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>

    rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token operator">++</span><span class="token punctuation">;</span>
    sendBytes <span class="token operator">+</span><span class="token operator">=</span> ret<span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>naluType <span class="token operator">&amp;</span> <span class="token number">0x1F</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">7</span> <span class="token operator">||</span> <span class="token punctuation">(</span>naluType <span class="token operator">&amp;</span> <span class="token number">0x1F</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">8</span><span class="token punctuation">)</span> <span class="token comment">// 如果是SPS、PPS就不需要加时间戳</span>
        <span class="token keyword">goto</span> out<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">else</span> <span class="token comment">// nalu长度小于最大包场：分片模式</span>
<span class="token punctuation">{<!-- --></span>
    <span class="token comment">/*
     *  0                   1                   2
     *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     * | FU indicator  |   FU header   |   FU payload   ...  |
     * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     */</span>

    <span class="token comment">/*
     *     FU Indicator
     *    0 1 2 3 4 5 6 7
     *   +-+-+-+-+-+-+-+-+
     *   |F|NRI|  Type   |
     *   +---------------+
     */</span>

    <span class="token comment">/*
     *      FU Header
     *    0 1 2 3 4 5 6 7
     *   +-+-+-+-+-+-+-+-+
     *   |S|E|R|  Type   |
     *   +---------------+
     */</span>

    <span class="token keyword">int</span> pktNum <span class="token operator">=</span> frameSize <span class="token operator">/</span> RTP_MAX_PKT_SIZE<span class="token punctuation">;</span>       <span class="token comment">// 有几个完整的包</span>
    <span class="token keyword">int</span> remainPktSize <span class="token operator">=</span> frameSize <span class="token operator">%</span> RTP_MAX_PKT_SIZE<span class="token punctuation">;</span> <span class="token comment">// 剩余不完整包的大小</span>
    <span class="token keyword">int</span> i<span class="token punctuation">,</span> pos <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>

    <span class="token comment">/* 发送完整的包 */</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span>i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> pktNum<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span>
    <span class="token punctuation">{<!-- --></span>
        rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">(</span>naluType <span class="token operator">&amp;</span> <span class="token number">0x60</span><span class="token punctuation">)</span> <span class="token operator">|</span> <span class="token number">28</span><span class="token punctuation">;</span>
        rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">=</span> naluType <span class="token operator">&amp;</span> <span class="token number">0x1F</span><span class="token punctuation">;</span>
        
        <span class="token keyword">if</span> <span class="token punctuation">(</span>i <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token comment">//第一包数据</span>
            rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">|</span><span class="token operator">=</span> <span class="token number">0x80</span><span class="token punctuation">;</span> <span class="token comment">// start</span>
        <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>remainPktSize <span class="token operator">==</span> <span class="token number">0</span> <span class="token operator">&amp;&amp;</span> i <span class="token operator">==</span> pktNum <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">//最后一包数据</span>
            rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">|</span><span class="token operator">=</span> <span class="token number">0x40</span><span class="token punctuation">;</span> <span class="token comment">// end</span>

        <span class="token function">memcpy</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>payload<span class="token operator">+</span><span class="token number">2</span><span class="token punctuation">,</span> frame<span class="token operator">+</span>pos<span class="token punctuation">,</span> RTP_MAX_PKT_SIZE<span class="token punctuation">)</span><span class="token punctuation">;</span>
        ret <span class="token operator">=</span> <span class="token function">rtpSendPacket</span><span class="token punctuation">(</span>socket<span class="token punctuation">,</span> ip<span class="token punctuation">,</span> port<span class="token punctuation">,</span> rtpPacket<span class="token punctuation">,</span> RTP_MAX_PKT_SIZE<span class="token operator">+</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>ret <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>

        rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token operator">++</span><span class="token punctuation">;</span>
        sendBytes <span class="token operator">+</span><span class="token operator">=</span> ret<span class="token punctuation">;</span>
        pos <span class="token operator">+</span><span class="token operator">=</span> RTP_MAX_PKT_SIZE<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/* 发送剩余的数据 */</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>remainPktSize <span class="token operator">&gt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
    <span class="token punctuation">{<!-- --></span>
        rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">(</span>naluType <span class="token operator">&amp;</span> <span class="token number">0x60</span><span class="token punctuation">)</span> <span class="token operator">|</span> <span class="token number">28</span><span class="token punctuation">;</span>
        rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">=</span> naluType <span class="token operator">&amp;</span> <span class="token number">0x1F</span><span class="token punctuation">;</span>
        rtpPacket<span class="token operator">-&gt;</span>payload<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">|</span><span class="token operator">=</span> <span class="token number">0x40</span><span class="token punctuation">;</span> <span class="token comment">//end</span>

        <span class="token function">memcpy</span><span class="token punctuation">(</span>rtpPacket<span class="token operator">-&gt;</span>payload<span class="token operator">+</span><span class="token number">2</span><span class="token punctuation">,</span> frame<span class="token operator">+</span>pos<span class="token punctuation">,</span> remainPktSize<span class="token operator">+</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        ret <span class="token operator">=</span> <span class="token function">rtpSendPacket</span><span class="token punctuation">(</span>socket<span class="token punctuation">,</span> ip<span class="token punctuation">,</span> port<span class="token punctuation">,</span> rtpPacket<span class="token punctuation">,</span> remainPktSize<span class="token operator">+</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>ret <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>

        rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>seq<span class="token operator">++</span><span class="token punctuation">;</span>
        sendBytes <span class="token operator">+</span><span class="token operator">=</span> ret<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

out:

<span class="token keyword">return</span> sendBytes<span class="token punctuation">;</span>

}

int main(int argc, char argv[])
{
int socket;
int fd;
int fps = 25;
int startCode;
struct RtpPacket rtpPacket;
uint8_t* frame;
uint32_t frameSize;

fd <span class="token operator">=</span> <span class="token function">open</span><span class="token punctuation">(</span>H264_FILE_NAME<span class="token punctuation">,</span> O_RDONLY<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>fd <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
    <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"failed to open %s\n"</span><span class="token punctuation">,</span> H264_FILE_NAME<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

socket <span class="token operator">=</span> <span class="token function">createUdpSocket</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>socket <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
    <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"failed to create socket\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

rtpPacket <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token keyword">struct</span> RtpPacket<span class="token operator">*</span><span class="token punctuation">)</span><span class="token function">malloc</span><span class="token punctuation">(</span><span class="token number">500000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
frame <span class="token operator">=</span> <span class="token punctuation">(</span>uint8_t<span class="token operator">*</span><span class="token punctuation">)</span><span class="token function">malloc</span><span class="token punctuation">(</span><span class="token number">500000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token function">rtpHeaderInit</span><span class="token punctuation">(</span>rtpPacket<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> RTP_VESION<span class="token punctuation">,</span> RTP_PAYLOAD_TYPE_H264<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span>
                <span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">0x88923423</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">while</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
    frameSize <span class="token operator">=</span> <span class="token function">getFrameFromH264File</span><span class="token punctuation">(</span>fd<span class="token punctuation">,</span> frame<span class="token punctuation">,</span> <span class="token number">500000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>frameSize <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
    <span class="token punctuation">{<!-- --></span>
        <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"read err\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">continue</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">startCode3</span><span class="token punctuation">(</span>frame<span class="token punctuation">)</span><span class="token punctuation">)</span>
        startCode <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
    <span class="token keyword">else</span>
        startCode <span class="token operator">=</span> <span class="token number">4</span><span class="token punctuation">;</span>

    frameSize <span class="token operator">-</span><span class="token operator">=</span> startCode<span class="token punctuation">;</span>
    <span class="token function">rtpSendH264Frame</span><span class="token punctuation">(</span>socket<span class="token punctuation">,</span> CLIENT_IP<span class="token punctuation">,</span> CLIENT_PORT<span class="token punctuation">,</span>
                        rtpPacket<span class="token punctuation">,</span> frame<span class="token operator">+</span>startCode<span class="token punctuation">,</span> frameSize<span class="token punctuation">)</span><span class="token punctuation">;</span>
    rtpPacket<span class="token operator">-&gt;</span>rtpHeader<span class="token punctuation">.</span>timestamp <span class="token operator">+</span><span class="token operator">=</span> <span class="token number">90000</span><span class="token operator">/</span>FPS<span class="token punctuation">;</span>

    <span class="token function">usleep</span><span class="token punctuation">(</span><span class="token number">1000</span><span class="token operator">*</span><span class="token number">1000</span><span class="token operator">/</span>fps<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token function">free</span><span class="token punctuation">(</span>rtpPacket<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">free</span><span class="token punctuation">(</span>frame<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>

}

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三、H.264 RTP打包的sdp描述

sdp文件有什么用？

sdp描述着媒体信息，当使用vlc打开这个sdp文件后，会根据这些信息做相应的操作（创建套接字…）,然后等待接收RTP包

这里给出RTP打包H.264的sdp文件，并描述每一行是什么意思

m=video 9832 RTP/AVP 96 
a=rtpmap:96 H264/90000
a=framerate:25
c=IN IP4 127.0.0.1

 

 
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这个一个媒体级的sdp描述，关于sdp文件描述详情可看从零开始写一个RTSP服务器（一）不一样的RTSP协议讲解

• m=video 9832 RTP/AVP 96

  格式为 m=<媒体类型> <端口号> <传输协议> <媒体格式 >
  媒体类型：video，表示这是一个视频流

  端口号：9832，表示UDP发送的目的端口为9832

  传输协议：RTP/AVP，表示RTP OVER UDP，通过UDP发送RTP包

  媒体格式：表示负载类型(payload type)，一般使用96表示H.264

• a=rtpmap:96 H264/90000

  格式为a=rtpmap:<媒体格式><编码格式>/<时钟频率>

• a=framerate:25

  表示帧率

• c=IN IP4 127.0.0.1

  IN：表示internet

  IP4：表示IPV4

  127.0.0.1：表示UDP发送的目的地址为127.0.0.1

特别注意：这段sdp文件描述的udp发送的目的IP为127.0.0.1，目的端口为9832

四、测试

讲上面给出的源码rtp.c、rtp.h、rtp_h264.c保存下来，然后编译运行

注意：该程序默认打开的是test.h264，如果你没有视频源，可以从RtspServer的example目录下获取

# gcc rtp.c rtp_h264.c
# ./a.out

 

 
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讲上面的sdp文件保存为rtp_h264.sdp，使用vlc打开，即可观看到视频

# vlc rtp_h264.sdp

 

 
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• 运行效果

  

至此，我们已经完成了RTSP协议交互和RTP打包H.264，下一篇文章就可以来实现一个播放H.264的RTSP服务器了