一、程序的邏輯主要分兩部分：
1、通過video4linux2讀取攝像頭的V4L2_PIX_FMT_YUYV格式的原始數據
2、把V4L2_PIX_FMT_YUYV格式的數據轉換成AV_PIX_FMT_YUV422P格式的yuv數據，並存放在AVFrame結構中； 把AVFrame結構送到編碼器；
收取編碼後的h264數據流，並存到文件中
二、代碼中主要用到的庫：
1、通過一個叫uvccapture-0.5庫（我直接改了裏面的代碼），獲取攝像頭的V4L2_PIX_FMT_YUYV格式數據。
2、通過libav編碼
三、主要代碼：
/*
* main.cpp
*
* Created on: 2014-3-2
* Author: xy
*/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <linux/videodev2.h>
//ffplay -f video4linux2 -framerate 30 -video_size hd720 /dev/video0
#ifdef __cplusplus
extern "C" {
#endif
#define __STDC_CONSTANT_MACROS
#ifdef _STDINT_H
#undef _STDINT_H
#endif
# include <stdint.h>
#include "libavformat/avformat.h"
#include "libavdevice/avdevice.h"
#include <libavutil/imgutils.h>
#include <libavutil/opt.h>
#ifdef __cplusplus
}
#endif
//輸入設備
#include "v4l2uvc.h"
int main() {
//v4l2 val
char *videodevice = "/dev/video0";
int width = 640; //320;
int height = 480; //240;
int brightness = 0, contrast = 0, saturation = 0, gain = 0;
int quality = 95;
int format = V4L2_PIX_FMT_YUYV;
struct vdIn *videoIn;
int grabmethod = 1;
//video encoder init
avcodec_register_all();
AVCodec *codec;
AVCodecContext *c = NULL;
int i, ret, x, y, got_output;
FILE *f;
AVFrame *frame;
AVPacket pkt;
uint8_t endcode[] = { 0, 0, 1, 0xb7 };
char filename[] = "test.264";
printf("Encode video file %s\n", filename);
/* find the mpeg1 video encoder */
codec = avcodec_find_encoder(AV_CODEC_ID_H264);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
/* put sample parameters */
c->bit_rate = 400000;
/* resolution must be a multiple of two */
c->width = width; // 352;
c->height = height; // 288;
/* frames per second */
c->time_base = (AVRational) {1,10/*25*/};
c->gop_size = 10; /* emit one intra frame every ten frames */
c->max_b_frames = 0; //1
c->pix_fmt = AV_PIX_FMT_YUV422P; //v4l2是這個格式 AV_PIX_FMT_YUV420P;
//av_opt_set(c->priv_data, "preset", "slow", 0);
av_opt_set(c->priv_data, "tune", "zerolatency", 0); //這個可以讓libav不緩存視頻幀
/********************************************************************************
* 有兩個地方影響libav是不是緩存編碼後的視頻幀，也就是影響實時性：
* 1、av_opt_set(c->priv_data, "tune", "zerolatency", 0);這個比較主要。
* 2、參數中有c->max_b_frames = 1;如果這個幀設爲0,就沒有B幀了，編碼會很快的。
********************************************************************************/
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "wb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
frame->format = c->pix_fmt;
frame->width = c->width;
frame->height = c->height;
/* the image can be allocated by any means and av_image_alloc() is
* just the most convenient way if av_malloc() is to be used */
ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height,
c->pix_fmt, 32);
if (ret < 0) {
fprintf(stderr, "Could not allocate raw picture buffer\n");
exit(1);
}
//v4l2 init
videoIn = (struct vdIn *) calloc(1, sizeof(struct vdIn));
if (init_videoIn(videoIn, (char *) videodevice, width, height, format,
grabmethod) < 0)
exit(1);
printf("w:%d,h:%d\n", c->width, c->height);
time_t timep;
timep = time(NULL);
printf("%s\n", asctime(gmtime(&timep)));
for (i = 0; i < 100; i++) {
//usleep(200000);
//從v4l2中獲取數據格式爲AV_PIX_FMT_YUV422P
if (uvcGrab(videoIn) < 0) {
fprintf(stderr, "Error grabbing\n");
close_v4l2(videoIn);
free(videoIn);
exit(1);
}
unsigned char *yuyv = videoIn->framebuffer;
//把數據複製到libav想要的結構中
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
printf("debug!!!");
fflush(stdout);
#if 0
/* prepare a dummy image */
/* Y */
for (y = 0; y < c->height; y++) {
for (x = 0; x < c->width; x++) {
frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
}
}
/* Cb and Cr */
for (y = 0; y < c->height/2; y++) {
for (x = 0; x < c->width/2; x++) {
frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
}
}
#else
/* prepare image */
/* Y Cb Rb */
for (y = 0; y < c->height; y++) {
for (x = 0; x < c->width; x++) {
frame->data[0][y * frame->linesize[0] + x] = yuyv[y
* frame->linesize[0] * 2 + 2 * x];
}
}
/* Cb and Cr */
for (y = 0; y < c->height; y++) {
for (x = 0; x < c->width / 2; x++) {
//frame->data[0][y * frame->linesize[0] + 2*x ] = yuyv[y*frame->linesize[0]*4+4*x];
//frame->data[0][y * frame->linesize[0] + 2*x+1] = yuyv[y*frame->linesize[0]*4+4*x+2];
frame->data[1][y * frame->linesize[1] + x] = yuyv[y
* frame->linesize[1] * 4 + 4 * x + 1];
frame->data[2][y * frame->linesize[2] + x] = yuyv[y
* frame->linesize[2] * 4 + 4 * x + 3];
}
}
#endif
frame->pts = i;
/* encode the image */
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
//編碼
}
/* get the delayed frames */
for (got_output = 1; got_output; i++) {
fflush(stdout);
ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
timep = time(NULL);
printf("%s\n", asctime(gmtime(&timep)));
/* add sequence end code to have a real mpeg file */
fwrite(endcode, 1, sizeof(endcode), f);
fclose(f);
avcodec_close(c);
av_free(c);
av_freep(&frame->data[0]);
av_frame_free(&frame);
printf("111\n");
free(videoIn);
}
想運行代碼的朋友可以通過這個文章：
http://blog.csdn.net/xyyangkun/article/details/20456725
編譯用到的libav庫
在通過改工程中的makefile：
LIBAVDIR=/home/xy/mywork/av/libav-2014-03-02
指定libav庫的位置就可以了。
使用的讀攝像頭數據的代碼出處：
庫的工程在代碼在：
http://download.csdn.net/detail/xyyangkun/6990791
所在工程已上傳到github:
https://github.com/xyyangkun/read_encoder_sender
提交版本：2e60986a438e731aa53ca7d54bc492c521e7b5bc