//create file
char *out = “./audio1.pcm”;
FILE *outfile = fopen(out,“wb+”);

//定义采集的音频设备序号
char *devicename =  "hw:0";

//register audio device
avdevice_register_all();


//get format
const AVInputFormat *iformat = av_find_input_format("alsa");

//open audio
if( (ret = avformat_open_input(&fmt_ctx, devicename, iformat, NULL)) < 0)
{
    av_strerror(ret, errors, 1024);
    printf("Failed to open audio device, [%d]%s\n", ret, errors);
    return;
};

av_init_packet(&pkt);
//read data form audio
while(ret = (av_read_frame(fmt_ctx, &pkt))== 0&&
        count++ < 5000)
{
     av_log(NULL, AV_LOG_INFO, "pkt size is %d（%p）, count=%d\n",pkt.size,pkt.data, count);
     fwrite(pkt.data, 1, pkt.size, outfile);
     fflush(outfile);
     av_packet_unref(&pkt);//release pkt

}