本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 # I/ q, |9 m# p4 p# c
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' h+ r L, x. X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.html2 u+ p: Q. H0 ]7 q6 ^& D7 ^, A
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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。 0 U: g' ?& |' s5 a. l. E

4 y" ^5 t. M& Y( A1 v: d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。
/ I9 s8 Y$ n8 o一、HTTP网页服务器
' `9 R# ^$ Y7 p C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)7 p2 C/ F4 j9 i. f [6 c8 s: B+ o
- {* W# z: |3 I4 c: y* e8 p
- struct sockaddr_in servaddr;9 L. l% g7 F2 A+ t ?3 X
- socklen_t addrsize = sizeof(struct sockaddr);1 {" o; L) L% d& e
- bzero(&servaddr , sizeof(servaddr));
3 Q& C8 I) q, M' O# u+ X9 b$ t( ~ - servaddr.sin_family = AF_INET;) j2 ]) w4 p: o, J- l
- servaddr.sin_addr.s_addr = inet_addr(ip);
7 K" Z4 N0 T/ e M) j. I: e' R - servaddr.sin_port = htons(port);* Y3 k( u% u3 {0 f% y; s
- int ret;5 W+ j/ o+ {- V$ M
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
, l- o' A) v5 P X W1 [ - {
& ^# Q K2 ?8 J1 t - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);/ Q0 X! }+ Q8 @$ U# |
- return -1;* d4 t# P, z0 T/ J; m1 P
- }
; }, U; Z' a+ s3 I) _ - int on = 1;* ]& ~# [5 l8 r: k1 M
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
$ I3 e9 G( Z- J( G- ~3 J# a - {
9 C& Y2 ~3 G f* o) |) L# M - printf("setsockopt error\n");5 X* F$ e( h8 z' V7 K4 v
- }
5 P: t1 @8 L- d! g1 s - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);/ c- u7 n& F$ w7 b9 ^; {. ^, o
- if(ret == -1)' N% B+ C- X- Y! J
- {- r/ m" u) z" w) J6 y& Y
- printf("Tcp bind faiLED!\n");
3 g7 @* l" t ?* u) g - return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");0 ~- D% k' Q* m0 I0 l( Y! v
- return -1;
f/ h6 [; |, d; Z# [- W) @ - }
6 Z0 q6 G' x3 L# L* }* U - return 0;9 P( s% _8 j5 p+ \- B- J
- }
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);% L$ Q+ Y, N9 x g$ O! l2 i1 \
- void * Thread_TCP_Web_Recv(void *arg)
- b/ C- m8 g4 K2 x' `9 v( r6 X' ^ - {
) M; f' T6 Y: O0 R3 P% Y. f: @ - 。。。
2 N" \+ Q; H: J# O' i1 R% p7 q - while(1)
% C4 r8 i4 h! V, A - {
8 C! i ]6 C% a5 A - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);3 k7 z% @4 R) L
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。5 V7 L3 U6 r; A! w+ C* S s" _% `
- }
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);
7 O0 @; n$ j5 A7 B: j - pic_tmpbuffer = pic.tmpbuffer;
1 X1 C9 w' @ M+ e, u- b/ @ - pic.tmpbytesused = buff.bytesused;; \& X" j4 {2 U+ ]5 B# D: f
- pic_tmpbytesused = pic.tmpbytesused;
* t$ q% `$ }) i9 L1 z - pthread_cond_broadcast(&pct);( g- c$ h9 @& P4 B2 v
- 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; T7 U" ^" m$ c8 U7 c# \- q4 u
- pthread_cond_t pct;; S: E6 {$ f" z; w
- int main(int argc, char* argv[])3 u- U, e9 W ?) U; a& m1 ~! G
- {
0 p2 |5 F" r! X) I - ...
1 h5 S8 O. D2 q& f - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);2 b6 k1 r3 E( L( f) A: t9 J
- pthread_mutex_init(&pmt , NULL);* A' S4 {) i: G+ L! f
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);. \; b1 Z9 q, p+ j( P$ I
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);5 T7 L0 b+ b8 O+ h8 w4 _
- ...
1 g' I$ B! H# W! v0 x& [) i - while(1)( ` ^- ~% U7 P- B3 l9 |& D
- {
1 h' C/ _! ~; I - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
9 C. _$ E- p4 L* Q - ...
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- ...5 X) G1 r* ]. s& I6 f5 _
- }
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;">6 B- I7 R1 ~) M2 Z0 s
- </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" \
6 @+ w X2 } y, [* X- X - "Server: MJPG-Streamer/0.2\r\n" \
/ E* K+ e _$ l! k" H - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
0 n/ g9 M6 E q9 S2 u1 d' q - "Pragma: no-cache\r\n" \
% j& @0 H K, G - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n". o6 ^3 G# @3 R5 C! A' h& }
- #define BOUNDARY "boundarydonotcross"
0 E3 s! N% a3 j6 { - printf("preparing header\n");
: }8 ~ b- K1 k, o9 T% Y - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
- N" F- p1 R# B# @ - "Access-Control-Allow-Origin: *\r\n" \+ d+ x5 w/ C1 s% c) A+ R* \- B
- STD_HEADER \, d4 u' v4 y# @0 C: \) y: z6 I
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \* \9 i3 c6 `8 L+ B$ T
- "\r\n" \ u- k* K0 |4 \2 M) J( e+ T
- "--" BOUNDARY "\r\n");
8 G$ I6 v5 C9 d. s1 t# ? - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
& m3 T. N: ~/ `; ?* }; k, `8 J - return;
; l6 ]( t y. P' B c: N3 @ - }
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" \
/ a; a1 W6 v% m1 f4 w$ x9 ~ - "Content-Length: %d\r\n" \+ ?2 r1 a+ V& B, d
- "X-Timestamp: %d.%06d\r\n" \- f9 d4 ^$ H3 |# F
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);0 e! z, [! P; O2 O
- printf("sending intemdiate header\n");. a& _7 y* V: g# S% \; l( Z
- if(write(fd, buffer, strlen(buffer)) < 0)
0 J) M/ g+ H/ t I# `- w - break;9 j x. x# s# T7 }( K$ V/ @
- printf("sending frame\n");; \( d. F* v9 j/ y* m/ f* @
- if(write(fd, frame, frame_size) < 0)
0 ]( V4 `% U, |: T* ? - break;5 o: [" B9 D: A" g
- printf("sending boundary\n");
9 j9 v% j, u, J3 E - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");9 F$ C4 k b+ P3 K7 m
- if(write(fd, buffer, strlen(buffer)) < 0)! c* i Z* P& }9 g+ m; `
- 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。  4 }6 B$ y, C8 A
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:! W k6 R+ F' j' F5 L1 u8 W+ O: m2 D
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)- g1 o3 ~/ W B
- {! R# I8 w& @; Q- i
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);/ @( e6 b) m$ T7 E' C4 _
- if(*socket_found == (~0))
* @0 k/ y6 w+ Z - {
) t8 b X) R7 n3 F: s - printf("Create udp send socket failed!\n");
, y+ L% Y! y- N. |; [; I - return -1;7 b: G4 y5 U6 N _
- } _8 |) E: G2 v" r
- addr->sin_family = AF_INET;
' `: Q, c: B8 F% { |) W - addr->sin_addr.s_addr = inet_addr(ip);
, i8 R6 f' t0 Q* Y! L - addr->sin_port = htons(port);$ i8 d2 Y/ y8 H* t [. }
- memset(addr->sin_zero, 0, 8);
/ B x- U5 q7 E9 O9 ~$ X$ k - return 0;
' x+ K) Z ~# l& @( V. a - }
复制代码 5 d1 i: ?4 n2 s4 g- M4 n Y5 M/ y
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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:0 X" K* h3 [3 f8 J9 V5 J1 Y
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9 F7 R5 ~* s/ @" P! k' {$ u
- while(fend > 0)% w& A- b3 x; k. Z7 {
- {
* B5 p; o2 E7 p4 b) c; A$ l - memset(picture.data , 0 , sizeof(picture.data));8 {. w3 V1 d4 \' i* U* @
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
' z# N, U' t% l3 @* S7 V& l - if(fend >= UDP_FRAME_LEN)
& ?- C' Z% g A& { }# z - {5 k4 g {/ n. ^* K% X p
- picture.length = UDP_FRAME_LEN;
( {6 ~6 m. J- i! C! G) Z - picture.fin = 0;
7 ?5 I9 @ g5 D4 I8 W - }' H8 F9 F' q ~4 B2 [' G w* _
- else# u v3 B$ f0 k, B2 b5 e
- {
9 k2 |* V" O$ e ]5 \7 M3 t - picture.length = fend;
, e* A8 J2 [% U+ Y" u- N" Y, `1 J+ g - picture.fin = 1;
) v' x" n5 j* }5 m- m, k - }
8 P: i$ C" n0 X& V1 T! l0 f - //printf("sendbytes = %d \n",sendbytes);" B0 f/ n) h) G
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
+ p; k- X+ F7 e3 N4 N; X+ i - if(sendbytes == -1)
) F% b* U9 j; m/ Q; f1 _1 i - {
, u0 Y) f$ S* k: Y# n+ z - printf("Send Picture Failed!d\n");
6 l3 d- m. i% r+ f) W" j: I - return -1;
# v# l4 P4 ?8 H+ a; a: i. S% p9 x - }9 R1 R' f* |, I3 g
- else
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- fend -= UDP_FRAME_LEN;& y( m/ t) e* G
- }
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复制代码 % s7 T9 I7 E& }/ e
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |