本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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.html4 y! K$ }5 C7 M% i9 G/ {# x
8 N0 L8 L7 Q( A$ A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。 - M4 l% w; W3 B! {

+ r- [* t8 ~; w" R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。
* Q I$ R- s" A7 s/ u一、HTTP网页服务器. P; J* A; B* m, T
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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9 H% f7 |7 a3 S - struct sockaddr_in servaddr;9 Y2 p# t- f1 J- a
- socklen_t addrsize = sizeof(struct sockaddr);, {& `2 u- E Q4 J) T( |; O
- bzero(&servaddr , sizeof(servaddr));4 _5 W6 j* H7 k$ A3 w- i
- servaddr.sin_family = AF_INET;3 w/ g @8 B) I4 h0 ]; j
- servaddr.sin_addr.s_addr = inet_addr(ip);# {& h+ F; x9 l2 G8 c. k
- servaddr.sin_port = htons(port);
) M, |* i1 U! p4 G - int ret;1 X6 F' \1 T" V! }
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)" {: s- s/ P0 ?- N& e" ~2 `
- {
7 \* s: Z) U& Z8 b) B' }$ @7 V- X - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
- H: i# [$ M& k0 D+ ~6 o6 g - return -1;: }- G! x2 S$ t2 }
- }
6 K2 n# W" {8 o/ r6 B - int on = 1;
1 I2 p6 j; e/ R$ \+ J - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)8 [6 [' K5 T) C% [. ]3 [- C
- {( b+ R& V7 s2 x+ _6 Q! l& k- Q1 b
- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
* w7 O/ s5 G( R& n - if(ret == -1)
: ?& g& s. W& E8 ^6 s - {
0 u# ^/ P+ i7 @) K+ B - printf("Tcp bind faiLED!\n");
: V/ V. I* H" |/ i - return -1;+ l- f% o) k+ O% O5 L; f
- }
1 ]% p. D5 I" r/ y- x; D+ s - if(listen(*socket_found , 5) == -1)/ ]4 F, b# A+ T' a X' T4 N2 P
- {- j3 _7 `. `0 P8 A
- printf("Listen failed!\n");
) s# g1 I7 {. V# v - return -1;
+ [" M" D4 u5 B! ^" R2 u! J4 r9 z5 | - }
' F& L( e) J8 N6 E2 v2 _ - return 0;1 |* X3 y" ?8 ~' s) {
- }
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);
) k% k* ?2 q6 u/ s; A - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
: ]1 \6 w% v& {3 B" e9 M - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
9 H. H9 ~# L4 J# p) a4 a& B - printf("fd_socket_conn = accept()\n");, q& ^$ |0 r, @! f& S( h/ ~7 y6 @
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
1 N5 v' p9 _7 Y9 c - }
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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);
' n& p; k/ `. m @ - pic_tmpbuffer = pic.tmpbuffer;2 w8 H7 g" s1 ]* `/ `
- pic.tmpbytesused = buff.bytesused;
8 G) ]( m, t* ~* p - pic_tmpbytesused = pic.tmpbytesused;
! w" Z; {: l' e5 t - pthread_cond_broadcast(&pct);
; A1 g5 N0 t! ^7 }+ f# l4 j - 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;% q4 z, P' f: i& {# f; P
- pthread_cond_t pct;
' b( L' |7 h% u - int main(int argc, char* argv[])- h6 z" T0 |& k8 p; r3 ^
- {
; Y: o9 a% D7 c& X s% r7 [ - ...
& i: A& v/ Q, B& R$ Y, Z - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
! \: v. t/ K' H* I) r7 g/ o - pthread_mutex_init(&pmt , NULL);9 g% |! I8 A) [9 u5 a
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
. V+ U3 l5 H# |" h/ d$ c4 S! K - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);* \& n5 _+ U9 d
- ...( i0 o, H* a" u5 l( d3 m5 }' e
- while(1)# ?% k. E7 k9 `; r: q" a, E
- {
' {* F7 e. B$ Z) b; I3 Q - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);3 d n9 w% M7 z7 V- O* t5 E
- ...
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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;"># U* H }1 \ c* `! b* f2 ~
- </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" \1 D8 c. f. _) X3 u+ D# Q& |
- "Server: MJPG-Streamer/0.2\r\n" \
! n- f) _' F5 I% s% z' k - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
6 \. ~; [( W/ j3 E' s! p/ i - "Pragma: no-cache\r\n" \# z' I5 @4 D6 D9 u% S
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"' R! o7 F7 F4 r; V3 n' e5 U
- #define BOUNDARY "boundarydonotcross"
9 |' N$ J( b8 `* s8 X - printf("preparing header\n");! a% T: Q: I% n8 t
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
5 z7 k! q6 g* F! ^2 \ - "Access-Control-Allow-Origin: *\r\n" \
1 @) }- @* b4 J2 ~( t$ \# b - STD_HEADER \
1 o5 O( H4 j3 z$ F& X5 }. e, v1 b1 D - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
( @9 o/ t3 i# E- W" X6 n - "\r\n" \
9 m* r' o. P4 K - "--" BOUNDARY "\r\n");
9 o$ u: `6 |" F9 ~& G7 g7 U/ ]) ^ - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);6 J9 m h* w/ ^: T' T
- 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" \; z/ P6 k5 a; } X+ H" @' y2 k
- "Content-Length: %d\r\n" \
3 G6 @, _' J1 f - "X-Timestamp: %d.%06d\r\n" \' T9 m3 Y+ w- h+ I5 _7 `
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
Z9 f/ j2 {0 U# X - printf("sending intemdiate header\n");$ I2 ?0 `& Q+ G
- if(write(fd, buffer, strlen(buffer)) < 0)
; N& U0 u( @; v: h - break;/ ?2 f1 e0 h1 r, r! w9 ]3 x) [& t! Z
- printf("sending frame\n");5 D) Y0 l# A( o
- if(write(fd, frame, frame_size) < 0)
[$ U# B: E3 V; ^, d - break;6 |* H" T0 _ q/ ~' Z
- printf("sending boundary\n");
. B* J3 o. k6 S. R. P9 z - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");0 l$ D! \8 {5 {. d; z+ ?/ H; I
- if(write(fd, buffer, strlen(buffer)) < 0)
3 ?# ~$ X3 Q7 F; O8 P, Z- } - 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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p6 A4 A1 v! x' z! H二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:* I! h; ]$ v4 O. N8 J9 |% M
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
) X/ @9 g0 L9 R/ a - {
, {4 h1 s3 x- Z4 q5 x ]- s- W" C! R - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
# A- X+ e* M- F7 H2 M6 ?' k8 G# g$ a- z - if(*socket_found == (~0))7 f4 e! ]4 V8 ?2 O! Q# O
- {
4 k; m" `* O+ D4 _! `8 | - printf("Create udp send socket failed!\n");
8 k& w1 i7 }, _3 S# ?. }+ q( j - return -1;7 V% |5 I- t& A7 r' t; [( L& s, z
- }
3 ?# C( ^1 |. o$ k% V' n - addr->sin_family = AF_INET;3 J( t5 b( {! [
- addr->sin_addr.s_addr = inet_addr(ip);& M% k) G9 N- d% A$ c4 @
- addr->sin_port = htons(port);
" `( `; v6 h6 |/ G+ m0 H% u - memset(addr->sin_zero, 0, 8);
L0 R. [3 |' X1 a) A - return 0;
" R. E. `& I' m- h7 q! L - }
复制代码 3 m& D# {5 q3 r# | P C
0 n% t2 m; {( X. K- T5 F% U! P, t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)
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( K/ ]( ]' B, ^$ a - memset(picture.data , 0 , sizeof(picture.data)); v- u/ J- c9 B) \3 J
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
+ m! H3 u1 A7 E - if(fend >= UDP_FRAME_LEN)
+ e- P- ^$ p; l/ B& t - {5 |$ V/ f- @4 ^( ?$ E
- picture.length = UDP_FRAME_LEN;9 W. q( Y6 ]- L
- picture.fin = 0;
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- else1 d/ A: t+ D5 r% O1 `* F' i) R: o
- {( `; J% \" {6 w% [1 x$ x
- picture.length = fend;4 S0 D. F; ~2 s h
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);) ?0 r7 [) m/ v. o, l
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);* R& \: ]# k( r, y, j- e
- if(sendbytes == -1)& X3 a9 `0 R, U6 h7 p3 b
- {' I: C4 } {) w! @! B+ m% `
- printf("Send Picture Failed!d\n");# I+ I; Z# {! w2 Y: o
- return -1;; U# o/ D, m1 ?$ N
- }
" \( h$ b5 J8 w* M - else+ A3 g$ {( ~7 f9 J
- {
7 N$ S# a1 u. x x7 W# t - fend -= UDP_FRAME_LEN;# y; d/ q) S6 [- B/ v$ @7 P/ g+ }
- }
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复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |