本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 7 h7 L! K6 S' Q" p1 o* s, F
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) I. u+ W- Q/ S1 n |7 B$ K作者|donatello1996 来源 | 电子发烧友 题图|飞凌嵌入式 iMX8MPlus 核心板: https://www.forlinx.com/product/136.html* m( ^9 b( \, [; Q' T
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本文采用的硬件板卡为飞凌嵌入式OKMX8MP-C开发板,系统版本Linux5.4.70+Qt5.15.0,主要介绍基于HTTP网页服务器和UDP上位机的MJPG码流传输。 MJPG格式作为一种持续传输的视频码流,在远程监控领域中应用较广,而实现这种远程监控的第三方应用最常见的有两种:浏览器HTTP网页、UDP上位机。 % i* b9 X8 P5 ?# Q' e9 ^/ j

! @9 a% f% t2 V1 N2 c; U两者各有优势,对比鲜明,其中: 这两种应用各有优缺点,对于嵌入式开发者来说,两者都必须掌握。
6 ?+ D6 W4 n" n; e一、HTTP网页服务器
* F, c8 r; j1 E* a先说下HTTP网页服务器获取MJPG码流的代码,首先是OKMX8MP-C在开发板端建立TCP服务器: - int TCP_Server_Found(socklen_t* socket_found , char* ip , int port)
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- struct sockaddr_in servaddr;" o; W6 [0 z; v8 h, b2 l% E7 n
- socklen_t addrsize = sizeof(struct sockaddr);
' a+ k9 l, Q$ H; m - bzero(&servaddr , sizeof(servaddr));
2 [5 U2 w9 t- u; G5 U) A1 g2 Y' q - servaddr.sin_family = AF_INET;3 K6 h4 Y0 f" f; ^
- servaddr.sin_addr.s_addr = inet_addr(ip);- S; F4 N! l7 t& M% M( F, ^. Y
- servaddr.sin_port = htons(port);8 N4 E) k; X9 D
- int ret;
3 J3 i* O4 D. V9 P, Y7 Z& u - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)* r; n! j9 _- u' O7 Z6 Y i6 ]
- {
# p7 x0 Z- m' U2 B% F1 D+ t - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
( @+ R* W4 K( g# J- [6 j# M4 g - return -1;5 F, d. r5 Y, F4 R; d) b
- }
) ?/ ], |3 a1 d! ` - int on = 1;: e' p, ~! \4 e% r1 B: p; }1 e
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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$ z: m7 ~# K& M$ _1 \ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);8 N9 j( p7 d3 w# ^9 Z" ]" }, Q' U
- if(ret == -1)1 Y; | V# W/ H* y
- {
" S0 L5 v# l# H/ X - printf("Tcp bind faiLED!\n");. _( G3 q3 d" c1 _
- return -1;
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- if(listen(*socket_found , 5) == -1)$ f0 L* {: l$ _. E
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- printf("Listen failed!\n");+ q9 U# u$ B% h: V8 B' o) b
- return -1;
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9 Y( S; Z( a1 f' C7 ?& D - return 0;+ [+ _4 K) H% B
- }
复制代码其中setsockopt()函数是可选的,一般只用于规避socket()函数的建立错误。 建立了TCP服务器后,返回的socklen_t型实参在后面的HTTP网页服务器中需要用到。 HTTP网页服务器所属的TCP操作是需要另起轮询线程来让客户端进行accept()握手操作的,accept()之前的listen()倒是只需要执行一次即可,accept()握手操作和recv()接收操作需要创建一个死循环线程: - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);+ C& I. W5 M9 Z V7 Q3 v
- void * Thread_TCP_Web_Recv(void *arg)
+ a \# {+ [5 X" c - {
/ W* o, x) K3 I - 。。。
7 I! ?' B# [4 D; W - while(1)
7 H% B7 }# r5 Q! c P - {
7 |; s& |0 @0 M& ] - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
% e/ s" {6 L+ H+ n- X( a- Y - printf("fd_socket_conn = accept()\n");' S1 Q7 _1 b" {- P
- 。。。
0 q- c) m- l) z3 @- `8 f8 Z* } - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- }
复制代码MJPG帧可以使用Grab操作获取,获取到的MJPG帧需要在TCP线程中读,在Grab操作线程中写,这种被多个线程访问的资源需要加锁防止读写冲突,即资源被Grab操作写入时,需要上锁,不允许其它线程访问,操作完成时需要解锁,允许其它线程访问: - pthread_mutex_lock(&pmt);
* m( t' y9 e; q& K" `9 @ - pic_tmpbuffer = pic.tmpbuffer;1 Z3 z+ P; u# u4 w# K5 D
- pic.tmpbytesused = buff.bytesused;
/ e U$ f) B$ y' w: [' x# l - pic_tmpbytesused = pic.tmpbytesused; U) J7 T, W+ p. i! h, Y
- pthread_cond_broadcast(&pct);$ A! O# q; i3 r+ z# h
- pthread_mutex_unlock(&pmt);
复制代码线程互斥锁使用之前需要初始化: - pthread_mutex_t pmt;
& D/ {; e$ Z- ]2 i9 b9 t' j, C- K - pthread_cond_t pct;
' o7 I% d6 D: v+ m - int main(int argc, char* argv[])
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- ...
( b8 N; \ z! E7 _) M6 g - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);$ g" ]4 y7 c- L* V% v7 _7 _, a% {
- pthread_mutex_init(&pmt , NULL);! ^, {$ ~" C2 \# B' c" k1 Z. o' Q
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);9 i; {4 }% }* c4 q: [ `
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);2 r6 Z k2 e4 ~6 _
- ...
( {6 F/ M; ~' c$ d - while(1)7 _& k2 ?! C& h( ?
- {
( m5 W) S2 _- w" ` P: M+ a) S - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);9 o3 R& J# N8 C3 @3 `
- ...
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% u" O/ b: p' b - ...
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复制代码然后是发送的细节,发送图片文件之前,需要先发送HTTP标准头,这个相当于给发送图片或者其它类型的流数据铺路: - <p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"><span style="text-indent: 32px;">' x# |! u' L0 O$ n, V$ D! x
- </span></p><p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"></p>
复制代码- #define STD_HEADER "Connection: close\r\n" \3 ?/ L! H S' C K# q+ M; o
- "Server: MJPG-Streamer/0.2\r\n" \9 ?# E7 f: I0 w: W+ R/ J! m
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
r C' ]* ]$ _+ o. u* Q - "Pragma: no-cache\r\n" \
( @7 V8 I6 I6 [* F( @ - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
0 v8 \, d, S4 { - #define BOUNDARY "boundarydonotcross"& Y! \% b2 F! x
- printf("preparing header\n");
C$ e$ q1 N# Y - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ H: t% f3 h% O6 W# A3 T
- "Access-Control-Allow-Origin: *\r\n" \
0 {& j0 z q5 r7 q- D - STD_HEADER \
( f2 N& e0 Q$ K) n. g' [: a - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \. m! k- H! G% K( e) R3 s2 D
- "\r\n" \: L0 u' R E' W# O' D, L( o; d- }
- "--" BOUNDARY "\r\n");
% t3 p6 s5 O% E6 j& t - if(write(fd, buffer, strlen(buffer)) < 0)( H, i) U' A% o: ^% w
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- free(frame);- u( ]- w0 C- C
- return;
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复制代码发送完HTTP标准头之后,就需要发送内容头(Content-Type),这处的Content-Type为image/jpeg,同样,HTTP标准协议里面image支持的类型远不止jpeg一种,发送完内容头之后就是正文和boundary结尾,这样帧完整的HTTP头发送到指定的TCP GET地址,就会在浏览器中显示刚刚发送的图片: - <pre class="prettyprint lang-cpp" style="box-sizing: border-box; font-family: Monaco, Menlo, Consolas, "Courier New", monospace; font-size: 16px; white-space: pre-wrap; line-height: 1.38462; color: rgb(51, 51, 51); word-break: break-all; background-color: rgb(245, 245, 245); border: 0px; border-radius: 4px; vertical-align: baseline;"> sprintf(buffer, "Content-Type: image/jpeg\r\n" \
7 t& p* z; j" @/ O: h& I& g - "Content-Length: %d\r\n" \
( ~; |5 h" u+ e' L - "X-Timestamp: %d.%06d\r\n" \$ e* j: J8 M4 g* }. k
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);) j3 g/ W: l6 c' ?$ i
- printf("sending intemdiate header\n");
. k! I5 m/ f4 P3 g. f; A" v - if(write(fd, buffer, strlen(buffer)) < 0)- L. b4 }1 M: f5 }8 Q
- break;6 x; g1 ?3 a, i, B! `
- printf("sending frame\n");" [0 A6 U/ |2 R) b( r; n
- if(write(fd, frame, frame_size) < 0)
" V3 I+ o( S# ~: S - break;! z0 S0 | n) f) K4 o; z
- printf("sending boundary\n");3 c4 L* y7 `+ x1 x5 c4 ~0 {" D
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");* ?. j) W) X" k' \; Q2 A" D
- if(write(fd, buffer, strlen(buffer)) < 0)
2 d& u( {( q6 s H: x6 g: U - break;</pre><p style="box-sizing: border-box; border: 0px; font-size: 16px; vertical-align: baseline; line-height: 26px; color: rgb(51, 51, 51); font-family: " helvetica="" neue",="" helvetica,="" tahoma,="" arial,="" "microsoft="" yahei",="" "hiragino="" sans="" gb",="" "wenquanyi="" micro="" hei",="" sans-serif;"=""></p>
复制代码另外需要说明的是,TCP服务器线程在发送MJPEG流的时候是死循环发送的,因此TCP客户端在发送完GET指令之后,就会收到TCP服务器循环发送的图像缓存,TCP客户端会陷入忙等待状态无法再对外发送任何GET或者POST指令,从客户端使用者角度来看的效果就是网页一直在等待。 
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
& }3 g7 L- ^% U- {- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
1 c. [! z i( | - {
: a1 w9 d! D6 o2 d - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* C1 g& O: Q. l! S
- if(*socket_found == (~0))
' D% _' z* y) t - {
o" K. ?; R( P6 P8 }% R - printf("Create udp send socket failed!\n");
0 v. q6 L8 r( ]9 e5 ]/ n/ o) o - return -1;4 J% c2 Z, |1 l
- }
' {+ C# @6 k: A1 q - addr->sin_family = AF_INET;
" M9 l2 x& }2 k# Q1 H1 y, ^ - addr->sin_addr.s_addr = inet_addr(ip);. r9 t& J' P/ U
- addr->sin_port = htons(port);
' t8 A; ?" {- G6 D - memset(addr->sin_zero, 0, 8);
" d9 X M) S1 U8 P/ b - return 0;
! h# M8 b* ?( }8 I& [ - }
复制代码 & M5 m! r# W* C6 U
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而UDP文件发送则要比HTTP发送简单得多,只需要将文件切片,每一片为固定长度的UDP帧长度,逐帧发送即可:
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- while(fend > 0)0 l5 a. J3 {2 j4 U% F
- {
3 ^1 o5 ], |/ \/ @/ g+ |+ {6 |: Q - memset(picture.data , 0 , sizeof(picture.data));
. {/ q% }8 m7 e3 X - fread(picture.data , UDP_FRAME_LEN , 1, fp);# u. [1 a. Z! i7 w; `6 u
- if(fend >= UDP_FRAME_LEN)+ A; d5 ^7 R8 v7 g
- {
5 O9 u! p- s4 ]( t - picture.length = UDP_FRAME_LEN;7 Q: q: [% E' M% Q
- picture.fin = 0;
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# E3 M$ g* N0 T& w - else3 q( Q, ?3 e. ?, X1 t" ~$ z6 \
- {
& z( v" s- I- z - picture.length = fend;
6 B$ k# z3 L0 _" g - picture.fin = 1;
% R$ L& c; K' ~) `! h9 q - }
# a3 J1 z3 C; M* c3 [ - //printf("sendbytes = %d \n",sendbytes);
h: i8 P6 X8 G# p- b - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
, x% s. s4 o9 D4 Z - if(sendbytes == -1)/ [* y8 k2 y; l3 W+ v
- {% H2 w% l5 T! e7 b
- printf("Send Picture Failed!d\n");
6 W# p3 _2 j( t. E# u - return -1;+ N3 a+ M" |* n# n4 O; D+ m9 X
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- else
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- fend -= UDP_FRAME_LEN;* M! ^& N2 E5 h
- }
% |1 ^, e ~; W D; d# c+ O3 { - }
复制代码
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z$ v) _' ^. a1 YiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |