文章目录

• 代码
• makefile

经过这几天的验证，终于走通了FFmpeg读取USB摄像头H264帧，然后用rtmp推流。使用的版本是4.0.2，网上的示例要么是命令形式的，要么是读取YUV格式的数据，然后在编码的，所以只能自己摸索了。
FFmpeg的源码在ubuntu16.04上的编译就不说了，这个网上的文章很多，这里我要说的是，好像FFmpeg对v4l2的封装，不能从摄像头多种输出格式数据中，选择

V4L2_PIX_FMT_H264

这种格式的数据输出，只能是默认的输出，这点还没有研究明白。
没办法只能写v4l2的操作，将数据保存到内存中，在用FFmpeg从内存中读取数据，最后用rtmp推流。
这里要非常感谢雷神的两篇博客：

• 最简单的基于FFmpeg的推流器（以推送RTMP为例）
• 最简单的基于FFmpeg的内存读写的例子：内存转码器

可以说没有这两篇博客，我还要摸索很久，可惜他不在世了；他的贡献现在还在让我们受益。

代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>
#include <fcntl.h>
#include <malloc.h>
#include <math.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/poll.h>
#include <linux/types.h>
#include <linux/videodev2.h>
#include <libavutil/time.h>
#include <libavutil/imgutils.h>
#include <libavutil/mathematics.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavdevice/avdevice.h>

#define DEV_TYPE		"video4linux2"
#define DEV_NAME		"/dev/video1"
#define MAX_CHANNEL 	(4)
#define AV_IO_BUF_SIZE	(96*1024)
#define CLEAR(x) 		memset(&(x), 0, sizeof(x))

struct buffer {
void   *start;
size_t length;
};

struct usbcamera_node
{
int channel;
char id[32];
int usb_port;
//V4L2
char devname[32];
int fd;
struct v4l2_format fmt;
struct v4l2_streamparm parm;
struct v4l2_requestbuffers req;
struct buffer *buffers;
int n_buffers;
int poll_index[MAX_CHANNEL];

};

struct usbcamera_node usbcamra;
struct pollfd usbcamra_poll_fd[MAX_CHANNEL];
nfds_t usbcamra_poll_fd_num = 0;
unsigned int frame_len = 0;
unsigned int frame_cnt = 0;

int avError(int errNum);

static int xioctl(int fh, int request, void *arg)
{
int r;
do
{
r = ioctl(fh, request, arg);
} while (-1 == r && EINTR == errno);

return r;
}

static int video_init(struct usbcamera_node *camera_node)
{
struct v4l2_capability cap;
struct v4l2_fmtdesc fmtdesc;
int ret = 0;

// open the video device with the API of open()
camera_node->fd = open(camera_node->devname, O_RDWR | O_NONBLOCK, 0);

if (-1 == camera_node->fd)
{
fprintf(stderr, "Cannot open '%s': %d, %s\n", camera_node->devname, errno, strerror(errno));
return -1;
}

// inquire video device capability with the API of ioctl
if (-1 == xioctl(camera_node->fd, VIDIOC_QUERYCAP, &cap))
{
fprintf(stderr, "%s is no V4L2 device\n", camera_node->devname);
return -1;
}

// Set video device settings
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE))
{
fprintf(stderr, "%s is no video capture device\n", camera_node->devname);
return -1;
}

if (!(cap.capabilities & V4L2_CAP_STREAMING))
{
fprintf(stderr, "%s does not support streaming i/o\n", camera_node->devname);
return -1;
}

printf("\nVIDOOC_QUERYCAP\n");
printf("the camera driver is: %s\n", cap.driver);
printf("the camera card is: %s\n", cap.card);
printf("the camera bus info is: %s\n", cap.bus_info);
printf("the version is: %d\n", cap.version);
printf("the capabilities is: 0x%x\n", cap.capabilities);
printf("the device_caps is: 0x%x\n", cap.device_caps);

fmtdesc.index = 0; //form number
fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;//frame type
while(ioctl(camera_node->fd, VIDIOC_ENUM_FMT, &fmtdesc) != -1)
{
printf("VIDIOC_ENUM_FMT success! fmtdesc.index:%d, fmtdesc.type:%d, fmtdesc.flags:%d, "
"fmtdesc.description:%s, fmtdesc.pixelformat:%d\n",
fmtdesc.index, fmtdesc.type, fmtdesc.flags, fmtdesc.description, fmtdesc.pixelformat);
fmtdesc.index ++;
}

if (-1 == xioctl(camera_node->fd, VIDIOC_S_FMT, &camera_node->fmt))
{
fprintf(stderr, "%s set fmt failed\n", camera_node->devname);
return -1;
}

printf("VIDIOC_S_FMT success! width:%d, height:%d, pixelformat:%x, field:%d, bytesperline:%d, "
"sizeimage:%d, colorspace:%d, priv:%d, flags:%x, ycbcr_enc:%d, quantization:%d, xfer_func:%d\n",
camera_node->fmt.fmt.pix.width, camera_node->fmt.fmt.pix.height, camera_node->fmt.fmt.pix.pixelformat,
camera_node->fmt.fmt.pix.field, camera_node->fmt.fmt.pix.bytesperline, camera_node->fmt.fmt.pix.sizeimage,
camera_node->fmt.fmt.pix.colorspace, camera_node->fmt.fmt.pix.priv, camera_node->fmt.fmt.pix.flags,
camera_node->fmt.fmt.pix.ycbcr_enc, camera_node->fmt.fmt.pix.quantization, camera_node->fmt.fmt.pix.xfer_func);

struct v4l2_streamparm parm = {0};
parm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
xioctl(camera_node->fd, VIDIOC_G_PARM, &parm);
parm.parm.capture.timeperframe.numerator = 1;
parm.parm.capture.timeperframe.denominator = camera_node->parm.parm.capture.timeperframe.denominator;
ret = xioctl(camera_node->fd, VIDIOC_S_PARM, &parm);
if(ret !=0 )
{
printf("line:%d parm set error, errno:%d, str:%s\n", __LINE__, errno, strerror(errno));
return -1;
}
printf("fd %d ret %d set Frame rate %.3f fps\n", camera_node->fd, ret,
1.0 * parm.parm.capture.timeperframe.denominator / parm.parm.capture.timeperframe.numerator);

// Require the Driver of V4L2 buffers for MMAP
if (-1 == xioctl(camera_node->fd, VIDIOC_REQBUFS, &camera_node->req))
{
if (EINVAL == errno)
{
fprintf(stderr, "%s does not support memory mapping\n", "USBCAMERA");
return -1;
}
else
{
return -1;
}
}

// Make the buffers map to the user space
for (camera_node->n_buffers = 0; camera_node->n_buffers < camera_node->req.count; ++camera_node->n_buffers)
{
struct v4l2_buffer buf;

CLEAR(buf);

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = camera_node->n_buffers;

if (-1 == xioctl(camera_node->fd, VIDIOC_QUERYBUF, &buf))
{
ret = -1;
break;
}

camera_node->buffers[camera_node->n_buffers].length = buf.length;
camera_node->buffers[camera_node->n_buffers].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE ,MAP_SHARED, camera_node->fd, buf.m.offset);
printf("mmap buffer index:%d buf %p length %d\n", camera_node->n_buffers, camera_node->buffers[camera_node->n_buffers].start, buf.length);

if (MAP_FAILED == camera_node->buffers[camera_node->n_buffers].start)
{
ret = -1;
break;
}
}
if((ret == -1) && (camera_node->n_buffers != 0))
{
for(ret = 0; ret < camera_node->n_buffers; ret++)
{
munmap(camera_node->buffers[camera_node->n_buffers].start, camera_node->buffers[camera_node->n_buffers].length);
printf("munmap buffer index:%d buf %p length %ld\n",
camera_node->n_buffers, camera_node->buffers[camera_node->n_buffers].start,
camera_node->buffers[camera_node->n_buffers].length);
}
return -1;
}

return 0;
}

static int start_capturing(struct usbcamera_node *camera_node)
{
unsigned int i;
enum v4l2_buf_type type;
int n_buffers = 0;

n_buffers = camera_node->n_buffers;
printf("start_capturing fd %d n_buffers %d\n", camera_node->fd, n_buffers);
for (i = 0; i < n_buffers; ++i)
{
struct v4l2_buffer buf;

CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;

if (-1 == xioctl(camera_node->fd, VIDIOC_QBUF, &buf))
{
printf("fd %d VIDIOC_QBUF faild\n", camera_node->fd);
return -1;
}
}
printf("fd %d VIDIOC_QBUF OK!\n", camera_node->fd);

type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl(camera_node->fd, VIDIOC_STREAMON, &type))
{
printf("fd %d VIDIOC_STREAMON faild\n", camera_node->fd);
return -1;
}
printf("fd %d VIDIOC_STREAMON Ok!\n", camera_node->fd);
return 0;
}

static int stop_capturing(struct usbcamera_node *camera_node)
{
enum v4l2_buf_type type;

type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl(camera_node->fd, VIDIOC_STREAMOFF, &type))
{
printf("fd %d VIDIOC_STREAMOFF faild\n", camera_node->fd);
return -1;
}
printf("fd %d VIDIOC_STREAMOFF Ok!\n", camera_node->fd);
return 0;
}

static int read_frame(struct usbcamera_node *camera_node, unsigned char *pbuf, unsigned int ch, struct timeval *tvl)
{
struct v4l2_buffer buf;
int count = 0;
int n_buffers = 0;

n_buffers = camera_node->n_buffers;
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (-1 == xioctl(camera_node->fd, VIDIOC_DQBUF, &buf))
{
switch (errno) {
case EAGAIN:
return 0;
case EIO:
/* Could ignore EIO, see spec. */
/* fall through */
default:
{
printf("VIDIOC_DQBUF faild\n");
return -1;
}
}
}

if(buf.index > n_buffers)
{
printf("buf.indx < n_buffers %d %d\n", buf.index, n_buffers);
return -1;
}

memcpy(pbuf, camera_node->buffers[buf.index].start, buf.bytesused);
tvl->tv_sec = buf.timestamp.tv_sec;
tvl->tv_usec = buf.timestamp.tv_usec;
count = buf.bytesused;

if (-1 == xioctl(camera_node->fd, VIDIOC_QBUF, &buf))
{
printf("VIDIOC_QBUF faild\n");
}

return count;
}

void free_camra_resource(struct usbcamera_node *camera_node)
{
int cnt = 0;
for(cnt = 0; cnt < camera_node->n_buffers; cnt++)
{
munmap(camera_node->buffers[cnt].start, camera_node->buffers[cnt].length);
printf("munmap buffer index:%d buf %p length %ld\n",
cnt, camera_node->buffers[cnt].start,
camera_node->buffers[cnt].length);
}
}

int read_buffer(void *opaque, uint8_t *pbuf, int buf_size)
{
struct timeval tvl;
if(poll(usbcamra_poll_fd, usbcamra_poll_fd_num, -1) == -1)
{
printf("usbcamra poll failed !!!!!!!!!!!!!\n");
return AVERROR_EXTERNAL;
}

if((usbcamra_poll_fd[0].revents & POLLERR) == POLLERR)
{
printf("usbcamra_poll_fd[0].revents 0x%x\n", usbcamra_poll_fd[0].revents);
return AVERROR_EXTERNAL;
}

if(usbcamra_poll_fd[0].revents && POLLIN)
{
frame_len = read_frame(&usbcamra, pbuf, 0, &tvl);
printf("frame_cnt:%d, frame_len:%d, tvl.tv_sec:%ld ", frame_cnt, frame_len, tvl.tv_sec);
printf("%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x "
"%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x \n",
pbuf[0],pbuf[1],pbuf[2],pbuf[3],pbuf[4],pbuf[5],pbuf[6],pbuf[7],pbuf[8],pbuf[9],pbuf[10],pbuf[11],
pbuf[12],pbuf[13],pbuf[14],pbuf[15],pbuf[16],pbuf[17],pbuf[18],pbuf[19],pbuf[20],pbuf[21],pbuf[22],
pbuf[23],pbuf[24],pbuf[25],pbuf[26],pbuf[27],pbuf[28],pbuf[29],pbuf[30],pbuf[31]);
}
frame_cnt++;
usbcamra_poll_fd[0].revents = 0;

if(frame_len > buf_size)
{
printf("frame_len is too big then buf_size\n");
return buf_size;
}
return (int)frame_len;

}

//ffmpeg -f v4l2 -list_formats all -i /dev/video0
//程序执行：./ffmpeg_usb_rtmp /dev/video0 1280 720 30 1500000
int main(int argc, char* argv[])
{
int videoindex = -1;
unsigned int frame_rate = 0;
//所有代码执行之前要调用av_register_all和avformat_network_init
//初始化所有的封装和解封装 flv mp4 mp3 mov。不包含编码和解码
av_register_all();
avformat_network_init();

if(argc != 5)
{
usbcamra.fmt.fmt.pix.width = 1280;
usbcamra.fmt.fmt.pix.height = 720;
frame_rate = 30;
}
else
{
usbcamra.fmt.fmt.pix.width = atoi(argv[2]);
usbcamra.fmt.fmt.pix.height = atoi(argv[3]);
frame_rate = atoi(argv[4]);
}

sprintf(usbcamra.devname, "%s", argv[1]);
printf("width:%d, height:%d, dev:%s", usbcamra.fmt.fmt.pix.width, usbcamra.fmt.fmt.pix.height, usbcamra.devname);

usbcamra.fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
usbcamra.fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_H264;
usbcamra.fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;

CLEAR(usbcamra.parm);
usbcamra.parm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
usbcamra.parm.parm.capture.timeperframe.numerator = 1;
usbcamra.parm.parm.capture.timeperframe.denominator = frame_rate;
CLEAR(usbcamra.req);
usbcamra.req.count = 16;
usbcamra.req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
usbcamra.req.memory = V4L2_MEMORY_MMAP;
usbcamra.buffers = calloc(usbcamra.req.count, sizeof(struct buffer));
if(!usbcamra.buffers)
{
fprintf(stderr, "calloc faild, errno:%d, str:%s\n", errno, strerror(errno));
return -1;
}

video_init(&usbcamra);
start_capturing(&usbcamra);
usbcamra_poll_fd[0].fd = usbcamra.fd;
usbcamra_poll_fd[0].events = POLLIN;
usbcamra_poll_fd_num = 1;

//输出的地址
const char *outUrl = "rtmp://192.168.1.102:1935/live";

//AVFormatContext **ps  输入封装的上下文。包含所有的格式内容和所有的IO。如果是文件就是文件IO，网络就对应网络IO
AVFormatContext *ifmt_ctx = NULL;

ifmt_ctx = avformat_alloc_context();
unsigned char* inbuffer=NULL;
inbuffer = (unsigned char*)av_malloc(AV_IO_BUF_SIZE);
if(inbuffer == NULL)
{
avformat_free_context(ifmt_ctx);
printf("line:%d av_malloc failed!\n", __LINE__);
return -1;
}
AVIOContext *avio_in = avio_alloc_context(inbuffer, AV_IO_BUF_SIZE, 0, NULL, read_buffer, NULL, NULL);
if(avio_in == NULL)
{
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
printf("line:%d avio_alloc_context failed!\n", __LINE__);
return -1;
}

ifmt_ctx->pb = avio_in;
ifmt_ctx->flags = AVFMT_FLAG_CUSTOM_IO;

//打开文件，解封文件头
int ret = avformat_open_input(&ifmt_ctx, NULL, NULL, NULL);
if (ret < 0)
{
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
avio_context_free(&avio_in);
return avError(ret);
}
printf("avformat_open_input success!\n");

ret = avformat_find_stream_info(ifmt_ctx, NULL);
if (ret != 0)
{
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
avio_context_free(&avio_in);
return avError(ret);
}
//打印视频视频信息
//0打印所有  inUrl 打印时候显示，
av_dump_format(ifmt_ctx, 0, NULL, 0);

AVFormatContext * ofmt_ctx = NULL;
//如果是输入文件 flv可以不传，可以从文件中判断。如果是流则必须传
//创建输出上下文
ret = avformat_alloc_output_context2(&ofmt_ctx, NULL, "flv", outUrl);
if (ret < 0)
{
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
avio_context_free(&avio_in);
avformat_free_context(ofmt_ctx);
return avError(ret);
}
printf("avformat_alloc_output_context2 success!\n");
printf("ifmt_ctx->nb_streams:%d\n", ifmt_ctx->nb_streams);
//查找到当前输入流中的视频流，并记录视频流的索引
unsigned int i;
for (i = 0; i < ifmt_ctx->nb_streams; i++)
{
//获取输入视频流
AVStream *in_stream = ifmt_ctx->streams[i];
if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
videoindex = i;
}
//为输出上下文添加音视频流（初始化一个音视频流容器）
AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
if (!out_stream)
{
printf("未能成功添加音视频流\n");
ret = AVERROR_UNKNOWN;
}

//将输入编解码器上下文信息 copy 给输出编解码器上下文
//ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
ret = avcodec_parameters_copy(out_stream->codecpar, in_stream->codecpar);
//ret = avcodec_parameters_from_context(out_stream->codecpar, in_stream->codec);
//ret = avcodec_parameters_to_context(out_stream->codec, in_stream->codecpar);
if (ret < 0)
{
printf("copy 编解码器上下文失败\n");
}
out_stream->codecpar->codec_tag = 0;

out_stream->codec->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER) {
out_stream->codec->flags = out_stream->codec->flags | AV_CODEC_FLAG_GLOBAL_HEADER;
}
}

printf("videoindex:%d\n", videoindex);
av_dump_format(ofmt_ctx, 0, outUrl, 1);

//打开IO
ret = avio_open(&ofmt_ctx->pb, outUrl, AVIO_FLAG_WRITE);
if (ret < 0)
{
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
avio_context_free(&avio_in);
avformat_free_context(ofmt_ctx);
return avError(ret);
}

//写入头部信息
ret = avformat_write_header(ofmt_ctx, 0);
if (ret < 0)
{
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
avio_context_free(&avio_in);
avformat_free_context(ofmt_ctx);
avError(ret);
}

printf("avformat_write_header Success!\n");
//推流每一帧数据
//int64_t pts  [ pts*(num/den)  第几秒显示]
//int64_t dts  解码时间 [P帧(相对于上一帧的变化) I帧(关键帧，完整的数据) B帧(上一帧和下一帧的变化)]  有了B帧压缩率更高。
AVPacket pkt;
//获取当前的时间戳  微妙
long long start_time = av_gettime();
long long frame_index = 0;
while (1)
{
//输入输出视频流
AVStream *in_stream, *out_stream;
//获取解码前数据
ret = av_read_frame(ifmt_ctx, &pkt);
if (ret < 0) break;

//PTS（Presentation Time Stamp）显示播放时间
//DTS（Decoding Time Stamp）解码时间
//没有显示时间（比如未解码的 H.264 ）
if (pkt.pts == AV_NOPTS_VALUE)
{
//AVRational time_base：时基。通过该值可以把PTS，DTS转化为真正的时间。
AVRational time_base1 = ifmt_ctx->streams[videoindex]->time_base;
//计算两帧之间的时间
int64_t calc_duration = (double)AV_TIME_BASE / av_q2d(ifmt_ctx->streams[videoindex]->r_frame_rate);
//配置参数
pkt.pts = (double)(frame_index*calc_duration) / (double)(av_q2d(time_base1)*AV_TIME_BASE);
pkt.dts = pkt.pts;
pkt.duration = (double)calc_duration / (double)(av_q2d(time_base1)*AV_TIME_BASE);
}

if (pkt.stream_index == videoindex)
{
AVRational time_base = ifmt_ctx->streams[videoindex]->time_base;
AVRational time_base_q = { 1,AV_TIME_BASE };
//计算视频播放时间
int64_t pts_time = av_rescale_q(pkt.dts, time_base, time_base_q);
//计算实际视频的播放时间
int64_t now_time = av_gettime() - start_time;

AVRational avr = ifmt_ctx->streams[videoindex]->time_base;
printf("avr.num:%d, avr.den:%d, pkt.dts:%ld, pkt.pts:%ld, pts_time:%ld\n",
avr.num,    avr.den,    pkt.dts,     pkt.pts,     pts_time);
if (pts_time > now_time)
{
//睡眠一段时间（目的是让当前视频记录的播放时间与实际时间同步）
printf("pts_time:%ld, now_time:%ld\n", pts_time, now_time);
av_usleep((unsigned int)(pts_time - now_time));
}
}

in_stream = ifmt_ctx->streams[pkt.stream_index];
out_stream = ofmt_ctx->streams[pkt.stream_index];

//计算延时后，重新指定时间戳
pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, (AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, (AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
pkt.duration = (int)av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
//字节流的位置，-1 表示不知道字节流位置,由程序自行探测
pkt.pos = -1;
if (pkt.stream_index == videoindex) {
printf("Send %8lld video frames to output URL\n", frame_index);
frame_index++;
}

ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
if (ret < 0)
{
printf("发送数据包出错\n");
break;
}
av_free_packet(&pkt);
}

stop_capturing(&usbcamra);
free_camra_resource(&usbcamra);
avformat_free_context(ifmt_ctx);
av_free((void*)inbuffer);
avio_context_free(&avio_in);
avformat_free_context(ofmt_ctx);
return 0;
}

int avError(int errNum) {
char buf[1024];
av_strerror(errNum, buf, sizeof(buf));
printf("failed!\n");
return -1;
}

程序运行方式：./ffmpeg_usb_rtmp /dev/video0 1280 720 30 1500000
有些USB摄像头支持命令设置H264编码率，但是这里没有写出来，因为不同厂家，命令不同，貌似v4l2没有这样统一的命令去设置编码率。
以上代码仅仅是测试读取USB摄像头H264帧进行rtmp推流的验证，直接在readbuffer函数使用poll读取数据，当帧率设置为30 时，存在丢帧播放花屏，这是因为使用的单线程，发送rtmp流的时候，不能去读数据，因此会丢帧。
另外也没有添加音频合成，然后在推流，后面接着弄吧，最终验证完之后，还要移植到imx6平台上。

makefile

TARGET		 = ffmpeg_usb_rtmp
LIB_PATH 	 = /usr/local/lib/

FFMPEG_LIBS = -lavutil -lavdevice -lavformat -lavcodec -lswresample -lavfilter -lswscale
SDL_LIBS	= -lSDL2
EXTRA_LIBS  = -lz -lm -lpthread -lstdc++ -lm -lrt -lpcre
ALL_LIBS	= $(EXTRA_LIBS) $(SDL_LIBS) $(FFMPEG_LIBS)

COMPILE_OPTS = -v -g -Wall -Wno-deprecated-declarations

C_COMPILER   = gcc
C_FLAGS 	 = $(CFLAGS) $(COMPILE_OPTS)
LD_FLAGS 	 = -L$(LIB_PATH) $(LDFLAGS)

SRC = ffmpeg_usb_rtmp.c

ALL:
$(C_COMPILER) $(C_FLAGS) $(LD_FLAGS) $(SRC) -o $(TARGET) $(ALL_LIBS)
clean:
rm -rf $(TARGET) *.o *.mp4 *.wav *.h264 *.avi *.flv

学习ffmpeg的路还有很长！