使用avilib封装MJPEG数据应用实例
发布日期：2021-06-29 12:42:13
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分类：技术文章
本文共 10847 字，大约阅读时间需要 36 分钟。
avilib 是一个很小的封装模块，它可以将一些图片数据封装成视频格式。在一些比较差的摄像头中，他们只支持V4L2_PIX_FMT_MJPEG 输出JPEG格式数据，以这种格式输出的数据，并不是标准的JPEG图片数据。因此，如果只是把MJPEG输出的所有文件存成一个文件，那么这个文件其实并不能播放。据网上的一些资料介绍，说是缺少Huffman 表，需要自己手动插入一个Huffman表。在一些嵌入式设备中，他们直接将MPEG模式下输出的数据，然后通过JPEG解码库解码成RGB数据，然后直接丢到LCD的BUFF中就可以了（这种方法我没有测试过，只是看网上资料这么介绍）。
本人主要开发嵌入式设备，且刚接触图形编码时间不久，暂时还没有使用一些大的图片格式转换库，库文件是在网上找的，avilib只有一个文件编译之后的大小也只有几十K，他可以直接将v4l2 MPEG模式输出的数据封装成avi格式视屏。它提供的接口有：
void AVI_set_video(avi_t *AVI, int width, int height, double fps, char *compressor);void AVI_set_audio(avi_t *AVI, int channels, long rate, int bits, int format, long mp3rate);int AVI_write_frame(avi_t *AVI, char *data, long bytes, int keyframe);int AVI_dup_frame(avi_t *AVI);int AVI_write_audio(avi_t *AVI, char *data, long bytes);int AVI_append_audio(avi_t *AVI, char *data, long bytes);long AVI_bytes_remain(avi_t *AVI);int AVI_close(avi_t *AVI);long AVI_bytes_written(avi_t *AVI);avi_t *AVI_open_input_file(char *filename, int getIndex);avi_t *AVI_open_fd(int fd, int getIndex);int avi_parse_input_file(avi_t *AVI, int getIndex);long AVI_audio_mp3rate(avi_t *AVI);long AVI_video_frames(avi_t *AVI);int AVI_video_width(avi_t *AVI);int AVI_video_height(avi_t *AVI);double AVI_frame_rate(avi_t *AVI);char* AVI_video_compressor(avi_t *AVI);int AVI_audio_channels(avi_t *AVI);int AVI_audio_bits(avi_t *AVI);int AVI_audio_format(avi_t *AVI);long AVI_audio_rate(avi_t *AVI);long AVI_audio_bytes(avi_t *AVI);long AVI_audio_chunks(avi_t *AVI);long AVI_max_video_chunk(avi_t *AVI);long AVI_frame_size(avi_t *AVI, long frame);long AVI_audio_size(avi_t *AVI, long frame);int AVI_seek_start(avi_t *AVI);int AVI_set_video_position(avi_t *AVI, long frame);long AVI_get_video_position(avi_t *AVI, long frame);long AVI_read_frame(avi_t *AVI, char *vidbuf, int *keyframe);int AVI_set_audio_position(avi_t *AVI, long byte);int AVI_set_audio_bitrate(avi_t *AVI, long bitrate);long AVI_read_audio(avi_t *AVI, char *audbuf, long bytes);long AVI_audio_codech_offset(avi_t *AVI);long AVI_audio_codecf_offset(avi_t *AVI);long AVI_video_codech_offset(avi_t *AVI);long AVI_video_codecf_offset(avi_t *AVI);int AVI_read_data(avi_t *AVI, char *vidbuf, long max_vidbuf, char *audbuf, long max_audbuf, long *len);void AVI_print_error(char *str);char *AVI_strerror();char *AVI_syserror();int AVI_scan(char *name);int AVI_dump(char *name, int mode);char *AVI_codec2str(short cc);int AVI_file_check(char *import_file);void AVI_info(avi_t *avifile);uint64_t AVI_max_size();int avi_update_header(avi_t *AVI);int AVI_set_audio_track(avi_t *AVI, int track);int AVI_get_audio_track(avi_t *AVI);int AVI_audio_tracks(avi_t *AVI);下面是一个简单的测试程序：
/*=============================================================================# FileName: main.c# Desc: this program aim to get image from USB camera,# used the V4L2 interface.# Author: Licaibiao# Version: # LastChange: 2016-12-10 # History:=============================================================================*/#include编译运行结果：#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "avilib.h"#define FILE_VIDEO "/dev/video0"#define JPG "./out/image%d.jpg"typedef struct{ void *start; int length;}BUFTYPE;BUFTYPE *usr_buf;static unsigned int n_buffer = 0; avi_t *out_fd = NULL; struct timeval time;float get_main_time(struct timeval* start , int update){ float dt; struct timeval now; gettimeofday(&now, NULL); dt = (float)(now.tv_sec - start->tv_sec); dt += (float)(now.tv_usec - start->tv_usec) * 1e-6; if (update > 0) { start->tv_sec = now.tv_sec; start->tv_usec = now.tv_usec; } return dt;}/*set video capture ways(mmap)*/int init_mmap(int fd){ /*to request frame cache, contain requested counts*/ struct v4l2_requestbuffers reqbufs; memset(&reqbufs, 0, sizeof(reqbufs)); reqbufs.count = 6; /*the number of buffer*/ reqbufs.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; reqbufs.memory = V4L2_MEMORY_MMAP; if(-1 == ioctl(fd,VIDIOC_REQBUFS,&reqbufs)) { perror("Fail to ioctl 'VIDIOC_REQBUFS'"); exit(EXIT_FAILURE); } n_buffer = reqbufs.count; printf("n_buffer = %d\n", n_buffer); //usr_buf = calloc(reqbufs.count, sizeof(usr_buf)); usr_buf = calloc(reqbufs.count, sizeof(BUFTYPE));/*** (4) *** / if(usr_buf == NULL) { printf("Out of memory\n"); exit(-1); } /*map kernel cache to user process*/ for(n_buffer = 0; n_buffer < reqbufs.count; ++n_buffer) { //stand for a frame struct v4l2_buffer buf; memset(&buf, 0, sizeof(buf)); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = n_buffer; /*check the information of the kernel cache requested*/ if(-1 == ioctl(fd,VIDIOC_QUERYBUF,&buf)) { perror("Fail to ioctl : VIDIOC_QUERYBUF"); exit(EXIT_FAILURE); } usr_buf[n_buffer].length = buf.length; usr_buf[n_buffer].start = (char *)mmap(NULL,buf.length,PROT_READ | PROT_WRITE,MAP_PRIVATE, fd,buf.m.offset); if(MAP_FAILED == usr_buf[n_buffer].start) { perror("Fail to mmap"); exit(EXIT_FAILURE); } }}int open_camera(void){ int fd; /*open video device with block */ fd = open(FILE_VIDEO, O_RDONLY); if(fd < 0) { fprintf(stderr, "%s open err \n", FILE_VIDEO); exit(EXIT_FAILURE); }; return fd;}int init_camera(int fd){ struct v4l2_capability cap; /* decive fuction, such as video input */ struct v4l2_format tv_fmt; /* frame format */ struct v4l2_fmtdesc fmtdesc; /* detail control value */ struct v4l2_control ctrl; int ret; /*show all the support format*/ memset(&fmtdesc, 0, sizeof(fmtdesc)); fmtdesc.index = 0 ; /* the number to check */ fmtdesc.type=V4L2_BUF_TYPE_VIDEO_CAPTURE; /* check video decive driver capability */ if(ret=ioctl(fd, VIDIOC_QUERYCAP, &cap)<0) { fprintf(stderr, "fail to ioctl VIDEO_QUERYCAP \n"); exit(EXIT_FAILURE); } /*judge wherher or not to be a video-get device*/ if(!(cap.capabilities & V4L2_BUF_TYPE_VIDEO_CAPTURE)) { fprintf(stderr, "The Current device is not a video capture device \n"); exit(EXIT_FAILURE); } /*judge whether or not to supply the form of video stream*/ if(!(cap.capabilities & V4L2_CAP_STREAMING)) { printf("The Current device does not support streaming i/o\n"); exit(EXIT_FAILURE); } printf("\ncamera driver name is : %s\n",cap.driver); printf("camera device name is : %s\n",cap.card); printf("camera bus information: %s\n",cap.bus_info); /*display the format device support*/ while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc)!=-1) { printf("\nsupport device %d.%s\n\n",fmtdesc.index+1,fmtdesc.description); fmtdesc.index++; } /*set the form of camera capture data*/ tv_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; /*v4l2_buf_typea,camera must use V4L2_BUF_TYPE_VIDEO_CAPTURE*/ tv_fmt.fmt.pix.width = 320; tv_fmt.fmt.pix.height = 240; tv_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG; /*V4L2_PIX_FMT_YYUV*/ tv_fmt.fmt.pix.field = V4L2_FIELD_NONE; /*V4L2_FIELD_NONE*/ if (ioctl(fd, VIDIOC_S_FMT, &tv_fmt)< 0) { fprintf(stderr,"VIDIOC_S_FMT set err\n"); exit(-1); close(fd); } init_mmap(fd);}int start_capture(int fd){ unsigned int i; enum v4l2_buf_type type; /*place the kernel cache to a queue*/ for(i = 0; i < n_buffer; i++) { struct v4l2_buffer buf; memset(&buf, 0, sizeof(buf)); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = i; if(-1 == ioctl(fd, VIDIOC_QBUF, &buf)) { perror("Fail to ioctl 'VIDIOC_QBUF'"); exit(EXIT_FAILURE); } } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if(-1 == ioctl(fd, VIDIOC_STREAMON, &type)) { printf("i=%d.\n", i); perror("VIDIOC_STREAMON"); close(fd); exit(EXIT_FAILURE); } return 0;}int process_image(void *addr, int length){#if 0 FILE *fp; static int num = 0; char image_name[20]; sprintf(image_name, JPG, num++); if((fp = fopen(image_name, "w")) == NULL) { perror("Fail to fopen"); exit(EXIT_FAILURE); } fwrite(addr, length, 1, fp); usleep(500); fclose(fp); return 0;#endif int res = 0; float ret = 0; //ret = get_main_time(&time , 1); res = AVI_write_frame(out_fd, addr, length,0); //ret = get_main_time(&time , 1); //printf("AVI write time = %f\n",ret); if(res < 0) { perror("Fail to write frame\n"); exit(EXIT_FAILURE); } return 0;}int read_frame(int fd){ struct v4l2_buffer buf; unsigned int i; memset(&buf, 0, sizeof(buf)); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; //put cache from queue if(-1 == ioctl(fd, VIDIOC_DQBUF,&buf)) { perror("Fail to ioctl 'VIDIOC_DQBUF'"); exit(EXIT_FAILURE); } assert(buf.index < n_buffer); //read process space's data to a file process_image(usr_buf[buf.index].start, usr_buf[buf.index].length); if(-1 == ioctl(fd, VIDIOC_QBUF,&buf)) { perror("Fail to ioctl 'VIDIOC_QBUF'"); exit(EXIT_FAILURE); } return 1;}int mainloop(int fd){ int count = 400; while(count-- > 0) { for(;;) { fd_set fds; struct timeval tv; int r; float ret = 0; ret = get_main_time(&time , 1); FD_ZERO(&fds); FD_SET(fd,&fds); /*Timeout*/ tv.tv_sec = 2; tv.tv_usec = 0; r = select(fd + 1,&fds,NULL,NULL,&tv); ret = get_main_time(&time , 1); //printf("AVI write time = %f\n",ret); if(-1 == r) { if(EINTR == errno) continue; perror("Fail to select"); exit(EXIT_FAILURE); } if(0 == r) { fprintf(stderr,"select Timeout\n"); exit(-1); } if(read_frame(fd)) { break; } } } return 0;}void stop_capture(int fd){ enum v4l2_buf_type type; type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if(-1 == ioctl(fd,VIDIOC_STREAMOFF,&type)) { perror("Fail to ioctl 'VIDIOC_STREAMOFF'"); exit(EXIT_FAILURE); }}void close_camera_device(int fd){ unsigned int i; for(i = 0;i < n_buffer; i++) { if(-1 == munmap(usr_buf[i].start,usr_buf[i].length)) { exit(-1); } } free(usr_buf); if(-1 == close(fd)) { perror("Fail to close fd"); exit(EXIT_FAILURE); }}void init_avi(void){ char *filename = "avi_test.avi"; out_fd = AVI_open_output_file(filename); if(out_fd!=NULL) { AVI_set_video(out_fd, 320, 240, 25, "MJPG"); } else { perror("Fail to open AVI\n"); exit(EXIT_FAILURE); }}void close_avi(void){ AVI_close(out_fd);}void main(void){ int fd; fd = open_camera(); init_avi(); init_camera(fd); start_capture(fd); mainloop(fd); stop_capture(fd); close_avi(); close_camera_device(fd);}
root@ubuntu:/home/share/test/v4l2_MJPEG_AVI# make cleanrm -f *.o a.out test core *~ *.aviroot@ubuntu:/home/share/test/v4l2_MJPEG_AVI# makegcc -c -o main.o main.cgcc -c -o avilib.o avilib.cgcc -o test main.o avilib.o root@ubuntu:/home/share/test/v4l2_MJPEG_AVI# ./test camera driver name is : gspca_zc3xxcamera device name is : PC Cameracamera bus information: usb-0000:02:00.0-2.1support device 1.JPEGn_buffer = 6root@ubuntu:/home/share/test/v4l2_MJPEG_AVI# lsavilib.c avilib.h avilib.o avi_test.avi main.c main.o Makefile testroot@ubuntu:/home/share/test/v4l2_MJPEG_AVI#生成的avi_est.avi 文件，在迅雷播放器上播放如下：
这里需要注意，可能是因为我的USB驱动问题，读取JPEG需要的时间过长，导致录制的视频，播放的时候会出现快进的问题。另外，如果在设置v4l2 内存映射的时候，如果申请的buff 块太少也是会导致数据采集过慢的问题。
完整的工程代码可以这里下载：
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