本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
& ?2 F3 a* C; h% n* v$ [) b+ u- u' i

( V7 R1 k( @* a7 P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
9 y6 b4 z% ~7 u5 [) o3 M h5 t7 Y; O/ y q
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。 ! ~' j$ T. @/ b

% m, D& e4 V7 m8 f% @8 f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。 * e7 B! I4 g4 D& Q) Z( D* V
一、HTTP网页服务器 Z( Z- j/ D: t1 i2 d
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)" E, V1 n( t: T, }. d
- {8 ~4 Y. ~8 B. J1 I$ h# A0 F V; }: \# t
- struct sockaddr_in servaddr;4 E' A0 G: v% B& O/ f. ]- Q* b
- socklen_t addrsize = sizeof(struct sockaddr);. q. W* T6 z5 P& e# r& e# l
- bzero(&servaddr , sizeof(servaddr));$ b. W+ b; F# |, a# J7 x0 }
- servaddr.sin_family = AF_INET;
: \/ Z6 [* S: i) E - servaddr.sin_addr.s_addr = inet_addr(ip);
0 ~8 m! g+ a) L$ ^8 g - servaddr.sin_port = htons(port);
2 }9 {1 ^ {2 N/ o - int ret;; P, m, r: V5 d! `) N8 E0 L, ~* Y
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
9 S5 T3 J/ R: f! |# `4 Y - {
. y- w1 Y/ |& k3 _$ V6 z. } - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);( K, }/ V' x0 i$ Z
- return -1;
% d2 I$ X: d/ i9 s5 n - }
. i% k- M: z4 D0 ~; V - int on = 1;
" m1 K) K0 B6 I, c( r - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
# f! Q9 o( N' g( ^ - {
) \6 H9 L' \. s; G5 N - printf("setsockopt error\n");
Y" s! E! N( {( \8 H2 n) G - }
& `; g7 n0 ~; e7 k3 U$ X - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);3 h6 d. c) H' k2 I& s. G. B8 x
- if(ret == -1)
: ^' E% ^+ g% o' a5 o. e5 d/ z - {- p5 s& Z" C W/ B# E- M: ]# r3 k
- printf("Tcp bind faiLED!\n");8 c1 ~' ^$ I" }; s
- return -1;+ |' w6 [ t* N5 @6 d: O
- }; } X2 y/ a- D1 a" r
- if(listen(*socket_found , 5) == -1)* K/ G; g8 Z0 y7 J7 v: a) p
- {$ ]7 f J% C( u/ d. ?% _& u" }$ z9 \
- printf("Listen failed!\n");
) m* ?# C* v- I! `5 z: F - return -1;
; E2 M$ `0 ?2 s6 D1 ` - }4 S8 X5 T0 L1 t& l- c+ F
- return 0;6 K4 |+ A" N' q" g- P- I
- }
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);$ z3 V% \- D; D: ~3 X' A* X
- void * Thread_TCP_Web_Recv(void *arg)
* x& e% ]+ |; j9 n" A - {
" E+ K% d& N, e6 b9 f - 。。。; S! X/ m) V6 o9 `
- while(1)- O! Y# A( R! v, m' H: d
- {
4 ?8 x: d( ?& F- Z5 p6 K% n5 X - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);1 d' `$ @1 R7 }
- printf("fd_socket_conn = accept()\n");% j; o) K& h5 }$ L
- 。。。
- A: _; Y% L& w" h: e - recv(fd_socket_conn , recvbuf , 1000 , 0);
# u. r0 x# Q3 g - }( B% x: a7 [4 t0 V) K9 R" ]
- 。。。$ ^; \+ d6 u: |+ N# e! A# i
- }
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);/ Z }, Z0 v) r. H8 o
- pic_tmpbuffer = pic.tmpbuffer;
! _! v) U* ?! Y5 w - pic.tmpbytesused = buff.bytesused;: v8 r/ [. d, P7 W+ }2 g
- pic_tmpbytesused = pic.tmpbytesused;9 [ x% L+ x7 g8 N/ I
- pthread_cond_broadcast(&pct);
3 a {6 q. |. m' t - 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;& V9 J% R5 a7 N1 t! P) m ]
- pthread_cond_t pct;0 T: Z. v$ T& Q
- int main(int argc, char* argv[]). g8 V) b9 t$ d! q: \" i
- {
$ w0 @5 S0 L+ w0 _ - ...4 ]) S$ l u/ y4 B1 [( M
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);' @) j0 ^9 ~( k7 S2 u
- pthread_mutex_init(&pmt , NULL);: h$ e; a1 u/ T0 G+ c
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
3 v) ]+ U% d' _0 `, C# B - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
]& }+ u( W* T% y - ...: W* n% N0 r/ U0 Q
- while(1)
$ Q6 Z$ m6 \6 T4 c2 m' k - {
% ?( ? a, i2 E, V2 F - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
+ f! C6 D% Z7 u; Y5 ^+ \ - .../ Z, K( l, h# B# B
- }
' T3 a& k9 B* m- F. K! c - ...
8 F/ E4 C6 L# q2 v( P, a+ ]; [' k - }
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;">
8 G9 G% N3 ~. 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" \) O8 n6 L, b p3 z p; W' @
- "Server: MJPG-Streamer/0.2\r\n" \
2 |1 W1 t0 N/ M9 y# S3 |5 ? - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \8 E! K8 N4 p6 L+ Z; @% y, b) j( z" W
- "Pragma: no-cache\r\n" \6 l# n/ A) O! k$ [3 G- S; o+ v
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"! ?/ T0 q) o" Q, o9 Q$ {. n
- #define BOUNDARY "boundarydonotcross"
9 ]2 [: A) D: G5 c - printf("preparing header\n");6 s) \$ L) q( U, Z. G. q0 ]
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \3 {3 e2 b0 F: H1 j
- "Access-Control-Allow-Origin: *\r\n" \
: }& N! W: z7 R: y1 p! ~ - STD_HEADER \/ b" H3 V b. B: @ Z. C
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \, l, ~; u! q8 l' c5 N
- "\r\n" \
+ j, z1 Q! X% Y2 L2 F - "--" BOUNDARY "\r\n");$ B: u- z0 q! J4 @4 z3 ]) @ V& u
- if(write(fd, buffer, strlen(buffer)) < 0)
$ l8 `' ]# |0 t5 d( z - {
! o& [# f# ^" Z* s# E. Y, p - free(frame);
1 ?0 i6 I, t5 K: o# b2 s1 ~0 [6 W - return;# B& r' f# f; d- K8 _
- }
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" \( J- ?! ~& Q) O- i5 W) @
- "Content-Length: %d\r\n" \4 |: n1 ~, b2 D9 a( {
- "X-Timestamp: %d.%06d\r\n" \. F: ?- U. B8 ~) O; s
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);7 s- V x- c5 D
- printf("sending intemdiate header\n");
4 V& h/ _) d) m" _% D. k7 s3 r) u3 } - if(write(fd, buffer, strlen(buffer)) < 0)
0 C! [4 E. ` t& \! h - break;1 ^6 v, ]- X' `4 h5 O' E
- printf("sending frame\n");5 U2 _5 ^* C* g. v7 b0 I
- if(write(fd, frame, frame_size) < 0)
- t5 E [3 j/ D! l. O' Z - break;
" X. p* T( N3 `' @" Y/ t5 d0 ]! H; n - printf("sending boundary\n");
; D/ L7 n$ h4 V - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");0 @' r$ f! o" Q, Q. U. n- a3 @
- if(write(fd, buffer, strlen(buffer)) < 0) q" i( D w. ~4 H0 O6 ~
- 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。 
- X% z. V$ l; s$ F2 |
, \8 p! J/ l3 [6 G0 R v5 u二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:5 U; I$ |7 u, d" ~9 j+ n' Q! K7 n
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
7 M0 o, p* e8 o3 _0 c4 W - {/ C, N% X1 ^( \3 g7 [: }
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
9 ^/ ~% |: f! ^4 w9 v - if(*socket_found == (~0)); w& b; ^. }$ P! r7 u
- { e- q$ Y; d0 O3 `' E& b) a
- printf("Create udp send socket failed!\n");; X- p7 I( t7 m+ ?6 S2 W
- return -1;
! c; y" y) c0 T. V( s3 W - } F4 Q! W- _( j6 M/ U' _: _: P
- addr->sin_family = AF_INET;5 |# L* J: H3 y/ @
- addr->sin_addr.s_addr = inet_addr(ip);
& g& `4 W' A Y: ?) C, z - addr->sin_port = htons(port);
1 }+ f: h0 E" W+ K0 z T( m - memset(addr->sin_zero, 0, 8);
1 E, O% l( p- H3 j - return 0;
( w1 \4 V: j! U# x q) ?# R - }
复制代码
4 K* e: p, k. k7 ^3 m
- H" `, }# Q- L1 J/ s4 ?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 u7 P% t* I) J# }, @. N& ]6 h" I1 d- `8 @: c% {2 N
, x+ X, x- `( T2 z- while(fend > 0)# O' @: w" T+ a# C5 r, j+ `1 {& v
- {
* f9 |! [- c" n3 T) H+ b" f - memset(picture.data , 0 , sizeof(picture.data));" d: x4 {8 m3 F$ v$ r& F
- fread(picture.data , UDP_FRAME_LEN , 1, fp);; x! Q6 }1 g! ^. P+ T
- if(fend >= UDP_FRAME_LEN)
s5 I- }, d3 k, ]4 `6 S - {
8 B- V8 g* O7 O& G2 w+ \( D - picture.length = UDP_FRAME_LEN;$ r, ]9 J( n. x
- picture.fin = 0;% O: }9 J7 F9 A
- }' |/ j C' w: {, Z. x+ h7 [
- else+ x2 s& K* N) q4 L; [
- {1 h. D3 n/ X3 T+ D" {
- picture.length = fend;
8 c+ G4 ]8 N6 o9 X5 c% F5 Z - picture.fin = 1;
* j& _+ e+ o7 v2 |3 z - }% s* R8 l& C3 b' N& i
- //printf("sendbytes = %d \n",sendbytes);
1 g. e8 W# l' q; r - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
% z8 C% q9 h% z B( t/ E9 ~ - if(sendbytes == -1)4 ^/ j0 ]( D5 t5 n
- {% d) w, y% y' u/ h
- printf("Send Picture Failed!d\n");
0 ?, P M( X) r5 g4 l& v - return -1;
; x! } w K% ~4 r - }/ x0 C4 r- v' V- i) ?- l! N
- else
' v. @7 d- }3 m: o% L# G - {& `" c8 [% Z' S8 t( N) n- r
- fend -= UDP_FRAME_LEN;
. c4 w* Q6 g( |# M) o9 G! s$ Z - }" i3 F1 p% ^2 J
- }
复制代码 4 {7 J+ E! |) o) c
" W. V3 n6 x' z - } w/ Q! S/ X% U
0 t5 S0 `. A% e$ u! |# ziMX8MPlus 核心板: https://www.forlinx.com/product/136.html |