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最近在學習FFMPEG,發現網上的很多例子都是基于讀檔案的。直接從攝像頭中讀取資料的卻很少。之前寫過通過v4l2采集攝像頭資料然後調用x264編碼成視訊檔案的例子。在FFMPEG中,它将很多的V4L2操作函數已經封裝好,這裡提供一個最簡的例程。需要注意的是,我采用的FFMPEG的版本是最新的ffmpeg-3.2.4 版本,不同版本的庫,接口函數有有些不一樣。
/*=============================================================================
# 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檔案如下:
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) $(OUT_APP) core *.core *~ *.jpeg
編譯運作結果如下:
licaibiao@ubuntu:~/test/FFMPEG/device$ ./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$
我使用的攝像頭輸出的是mjpeg格式資料,将它儲存到test.jpeg 檔案。打開如下:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiM0YTM1UTN1ETNxMDM3EDMy8CX0Vmbu4GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.jpg)