Mjpeg-streamer代码分析.doc

代码分析Mjpeg-streamer程序流程图：main()1参数分析2初始化全局变量global.stop = 0; global.buf = NULL; global.size = 0; global.in.plugin = NULL; /* this mutex and the conditional variable are used to synchronize access to the global picture buffer */3初始化互斥体和条件变量，来同步对global buffer的访问 if( pthread_mutex_init(&global.db, NULL) != 0 ) LOG(could not initialize mutex variablen); closelog(); exit(EXIT_FAILURE); if( pthread_cond_init(&global.db_update, NULL) != 0 ) LOG(could not initialize condition variablen); closelog(); exit(EXIT_FAILURE); 忽略管道断裂信号接受 ctrl +c 中止信号，并关闭系统日志服务的连接打开输入插件，并通过dlopen函数在RTLD_LAZY 指定模式打开指定的动态连接库文件，并返回一个句柄给调用进程使用dlsym获取函数入口地址，使gloabl的输入与动态库相关函数相关联。input_init()打开输出插件并通过dlopen函数，使用dlsym获取函数入口地址，使global的输出与相关函数关联output_init()input_run()开始读取，将图片存放在global buffer。ouput_run()pause()Intput_init()一分配视频数据结构二调用init_videoIn(videoIn, dev, width, height, fps, format,1)进行初始化，参数设置。*dev = /dev/video3, width=640, height=480, fps=5, format=V4L2_PIX_FMT_MJPEG,三 init_v4l2()1 打开设备文件。 int fd=open(/dev/video0,O_RDWR); 2. 取得设备的capability，看看设备具有什么功能，比如是否具有视频输入,或者音频输入输出等。VIDIOC_QUERYCAP,struct v4l2_capability 3. 选择视频输入，一个视频设备可以有多个视频输入。VIDIOC_S_INPUT,struct v4l2_input 4. 设置视频的制式和帧格式，制式包括PAL，NTSC，帧的格式个包括宽度和高度、帧格式等。 VIDIOC_S_STD,VIDIOC_S_FMT,struct v4l2_std_id,struct v4l2_format memset(&vd-fmt, 0, sizeof(struct v4l2_format); vd-fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; vd-fmt.fmt.pix.width = vd-width; vd-fmt.fmt.pix.height = vd-height; vd-fmt.fmt.pix.pixelformat = vd-formatIn; vd-fmt.fmt.pix.field = V4L2_FIELD_ANY; ret = ioctl(vd-fd, VIDIOC_S_FMT, &vd-fmt);5设置帧速率/*set framerate */ struct v4l2_streamparm *setfps; setfps = (struct v4l2_streamparm *) calloc(1, sizeof(struct v4l2_streamparm); memset(setfps, 0, sizeof(struct v4l2_streamparm); setfps-type = V4L2_BUF_TYPE_VIDEO_CAPTURE; setfps-parm.capture.timeperframe.numerator = 1; setfps-parm.capture.timeperframe.denominator = vd-fps; ret = ioctl(vd-fd, VIDIOC_S_PARM, setfps);6. 向驱动申请帧缓冲，NB_BUFFER=4/* * request buffers */ memset(&vd-rb, 0, sizeof(struct v4l2_requestbuffers); vd-rb.count = NB_BUFFER; vd-rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; vd-rb.memory = V4L2_MEMORY_MMAP; ret = ioctl(vd-fd, VIDIOC_REQBUFS, &vd-rb);7. 将申请到的帧缓冲映射到用户空间，这样就可以直接操作采集到的帧了，而不必去复制。vd-memi = mmap(0 /* start anywhere */ , vd-buf.length, PROT_READ, MAP_SHARED, vd-fd, vd-buf.m.offset); if (vd-memi = MAP_FAILED) perror(Unable to map buffer); goto fatal; 8. 将申请到的帧缓冲全部入队列，以便存放采集到的数据.VIDIOC_QBUF,struct v4l2_buffer ret = ioctl(vd-fd, VIDIOC_QBUF, &vd-buf);四分配一个tempbuffer 来重现图片Input_run()1为global全局变量分配一个buf，pglobal-buf = malloc(videoIn-framesizeIn);2 pthread_create(&cam, 0, cam_thread, NULL);创建cam_thread线程3pthread_detach(cam);Cam_thread()1使用uvcGrab来获取图像信息，若是mjpeg格式存入tmpbuffer若是YUYV格式存入framebuffer。while( !pglobal-stop ) /* grab a frame */if( uvcGrab(videoIn) buf中；若视频格式是MJPEG则memcpy_picture将tmpbuffer中的数据复制到pglobal-bufif (videoIn-formatIn = V4L2_PIX_FMT_YUYV) DBG(compressing framen); pglobal-size = compress_yuyv_to_jpeg(videoIn, pglobal-buf, videoIn-framesizeIn, gquality); else DBG(copying framen); pglobal-size = memcpy_picture(pglobal-buf, videoIn-tmpbuffer, videoIn-buf.bytesused); 3 pthread_cond_broadcast信号，给等待的输出线程发送信号。pthread_cond_broadcast(&pglobal-db_update);uvcGrab()1查看isstreaming是否为0，是0 则开启视频捕获，否则获取出队中的缓冲区的数据if (!vd-isstreaming if (video_enable(vd) goto err;memset(&vd-buf, 0, sizeof(struct v4l2_buffer); vd-buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; vd-buf.memory = V4L2_MEMORY_MMAP; ret = ioctl(vd-fd, VIDIOC_DQBUF, &vd-buf);switch (vd-formatIn) case V4L2_PIX_FMT_MJPEG: if (vd-buf.bytesused formatIn) case V4L2_PIX_FMT_MJPEG: if (vd-buf.bytesused tmpbuffer, vd-memvd-buf.index, vd-buf.bytesused); if (debug) fprintf(stderr, bytes in used %d n, vd-buf.bytesused); break; case V4L2_PIX_FMT_YUYV: if (vd-buf.bytesused vd-framesizeIn) memcpy (vd-framebuffer, vd-memvd-buf.index, (size_t) vd-framesizeIn); else memcpy (vd-framebuffer, vd-memvd-buf.index, (size_t) vd-buf.bytesused); break; default: goto err; break; 3把可用的缓冲区重新入队，ret = ioctl(vd-fd, VIDIOC_QBUF, &vd-buf);output_http.sooutput_init()output_parameter *param使用param指针填充context server结构体，打印出基本信息Output_run()创建server_thread 服务器线程pthread_create(&(serversid.threadID), NULL, server_thread, &(serversid);pthread_detach(serversid.threadID);server_thread()TCP服务器：1为服务器创建socket套接字2填充addr结构体3bind绑定4listen设置监听套接字5 accept循环接收连接请求6创建线程client_thread线程，来处理此次的客户端连接。Client_thread()1初始化iobuffer 指针iobuf request指针 req init_iobuffer(&iobuf); init_request(&req);2 读取请求 memset(buffer, 0, sizeof(buffer); if ( (cnt = _readline(lcfd.fd, &iobuf, buffer, sizeof(buffer)-1, 5) = -1 ) close(lcfd.fd); return NULL; 3分析请求资源命令，发送相应的内容 /* determine what to deliver */ if ( strstr(buffer, GET /?action=snapshot) != NULL ) req.type = A_SNAPSHOT; else if ( strstr(buffer, GET /?action=stream) != NULL ) req.type = A_STREAM; else if ( strstr(buffer, GET /?action=command) != NULL ) int len;req.type = A_COMMAND; switch ( req.type ) case A_SNAPSHOT: DBG(Request for snapshotn); send_snapshot(lcfd.fd); break; case A_STREAM: DBG(Request for streamn); send_stream(lcfd.fd); break; case A_COMMAND: if ( lcfd.pc-conf.nocommands ) send_error(lcfd.fd, 501, this server is configured to not accept commands); break; command(lcfd.pc-id, lcfd.fd, req.parameter); break; case A_FILE: if ( lcfd.pc-conf.www_folder = NULL ) send_error(lcfd.fd, 501, no www-folder configured); else send_file(lcfd.pc-id, lcfd.fd, req.parameter); break; default: DBG(unknown requestn); send_snapshot1等待新一帧pthread_cond_wait(&pglobal-db_update, &pglobal-db);2将帧数据拷贝到frame中memcpy(frame, pglobal-buf, frame_size);3互斥体解锁pthread_mutex_unlock( &pglobal-db );4 HTTP响应也是由三个部分组成，分别是：状态行、消息报头、响应正文。将http回应 写入buffer中，先发送http状态行和消息包头，发送帧数据，之后释放frame缓存区 /* write the response */ sprintf(buffer, HTTP/1.0 200 OKrn STD_HEADER Content-type: image/jpegrn rn); /* send header and image now */ if( write(fd, buffer, strlen(buffer) 0 ) free(frame); return; write(fd, frame, frame_size); free(frame);send_streamHTTP响应也是由三个部分组成，分别是：状态行、消息报头、响应正文1 发送回应报头状态行，并返回边界字符串，与上帧图片可以区别开，下一帧图片开始。这是在context type的boundary子属性来指明的。sprintf(buffer, HTTP/1.0 200 OKrn STD_HEADER Content-Type: multipart/x-mixed-replace;boundary= BOUNDARY rn rn - BOUNDARY rn); if ( write(fd, buffer, strlen(buffer) buf, frame_size);3发送类型和长度sprintf(buffer, Content-Type: image/jpegrn Content-Length: %drn rn, frame_size)