系列相关博文：
最近在学习FFMPEG，发现网上的很多例子都是基于读文件的。直接从摄像头中读取数据的却很少。之前写过通过v4l2采集摄像头数据然后调用x264编码成视频文件的例子。在FFMPEG中，它将很多的V4L2操作函数已经封装好，这里提供一个最简的例程。需要注意的是，我采用的FFMPEG的版本是最新的ffmpeg-3.2.4 版本，不同版本的库，接口函数有有些不一样。
- /*=============================================================================
- # FileName: read_device.c
- # Desc: use ffmpeg read a frame data from v4l2
- # Author: licaibiao
- # LastChange: 2017-03-15
- =============================================================================*/
- #include <stdio.h>
- #include <string.h>
- #include <stdlib.h>
- #include <unistd.h>
- #include "avformat.h"
- #include "avcodec.h"
- #include "avdevice.h"
- char* input_name= "video4linux2";
- char* file_name = "/dev/video0";
- char* out_file = "test.jpeg";
- void captureOneFrame(void){
- AVFormatContext *fmtCtx = NULL;
- AVPacket *packet;
- AVInputFormat *inputFmt;
- FILEFILE *fp;
- int ret;
- inputFmt = av_find_input_format (input_name);
- if (inputFmt == NULL) {
- printf("can not find_input_format\n");
- return;
- }
- if (avformat_open_input ( &fmtCtx, file_name, inputFmt, NULL) < 0){
- printf("can not open_input_file\n"); return;
- }
- /* print device information*/
- av_dump_format(fmtCtx, 0, file_name, 0);
- packet = (AVPacket *)av_malloc(sizeof(AVPacket));
- av_read_frame(fmtCtx, packet);
- printf("data length = %d\n",packet->size);
- fp = fopen(out_file, "wb");
- if (fp < 0) {
- printf("open frame data file failed\n");
- return ;
- }
- fwrite(packet->data, 1, packet->size, fp);
- fclose(fp);
- av_free_packet(packet);
- avformat_close_input(&fmtCtx);
- }
- int main(void){
- avcodec_register_all();
- avdevice_register_all();
- captureOneFrame();
- return 0;
- }
Makefile文件如下：
- OUT_APP = test
- INCLUDE_PATH = /usr/local/include/
- INCLUDE = -I$(INCLUDE_PATH)libavutil/ -I$(INCLUDE_PATH)libavdevice/ \
- -I$(INCLUDE_PATH)libavcodec/ -I$(INCLUDE_PATH)libswresample \
- -I$(INCLUDE_PATH)libavfilter/ -I$(INCLUDE_PATH)libavformat \
- -I$(INCLUDE_PATH)libswscale/
- FFMPEG_LIBS = -lavformat -lavutil -lavdevice -lavcodec -lswresample -lavfilter -lswscale
- SDL_LIBS =
- LIBS = $(FFMPEG_LIBS)$(SDL_LIBS)
- COMPILE_OPTS = $(INCLUDE)
- C = c
- OBJ = o
- C_COMPILER = cc
- C_FLAGS = $(COMPILE_OPTS) $(CPPFLAGS) $(CFLAGS)
- LINK = cc -o
- LINK_OPTS = -lz -lm -lpthread
- LINK_OBJ = read_device.o
- .$(C).$(OBJ):
- $(C_COMPILER) -c -g $(C_FLAGS) $<
- $(OUT_APP): $(LINK_OBJ)
- $(LINK)$@ $(LINK_OBJ) $(LIBS) $(LINK_OPTS)
- clean:
- -rm -rf *.$(OBJ) $(OUT_APP) core *.core *~ *.jpeg
编译运行结果如下：
- licaibiao@ubuntu:~/test/FFMPEG/device$ ./test
- [video4linux2,v4l2 @ 0x1d18040] Time per frame unknown
- Input #0, video4linux2,v4l2, from '/dev/video0':
- Duration: N/A, bitrate: N/A
- Stream #0:0: Video: mjpeg, none, 640x480, 1000k tbn
- data length = 27697
- licaibiao@ubuntu:~/test/FFMPEG/device$ ls
- Makefile read_device.c read_device.o test test.jpeg webcm.c
- licaibiao@ubuntu:~/test/FFMPEG/device$
我使用的摄像头输出的是mjpeg格式数据，将它保存到test.jpeg 文件。打开如下：