前面一篇博客介绍在centos上搭建点击打开链接ffmpeg及x264开发环境。以下就来问个样例：

1、利用x264库将YUV格式视频文件编码为h264格式视频文件

2、利用ffmpeh库将h264格式的视频文件解码为yuv格式视频文件

解码和编码前后对文件大小进行比較，如图：

当中yuv420p.yuv为原始文件，大小77M

encode.h264为H264编码后的视频文件，大小1.4M

decode.yuv为ffmpeg解码后的视频文件，大小77M。

从文件的大小非常明显能够看出h264压缩率。在Ｗｉｎｄｏｗｓ平台分辨播放了三个文件，画面看不出差别。

以下是代码＂

/*File : yuvTO264.c

 *Auth : sjin

 *Date : 20141115

 *Mail : 413977243@qq.com

 */

/*利用x264库将YUV文件编码为h264文件

 *

 */

#include <stdint.h>

#include <x264.h>

#include <stdio.h>

#include <unistd.h>

#include <fcntl.h>

#include <stdlib.h>

#include <string.h>

#define CLEAR(x) (memset((&x),0,sizeof(x)))

#define IMAGE_WIDTH   176

#define IMAGE_HEIGHT  144

#define ENCODER_PRESET "veryfast"

/*配置參数

 * 使用默认參数，在这里使用了zerolatency的选项，使用这个选项之后，就不会有

 * delayed_frames，假设你使用不是这个的话，还须要在编码完毕之后得到缓存的

 * 编码帧

 */

#define ENCODER_TUNE   "zerolatency"

#define ENCODER_PROFILE  "baseline"

#define ENCODER_COLORSPACE X264_CSP_I420

typedef struct my_x264_encoder{

        x264_param_t  * x264_parameter;

        char parameter_preset[20];

        char parameter_tune[20];

        char parameter_profile[20];

        x264_t  * x264_encoder;

        x264_picture_t * yuv420p_picture;

        long colorspace;

        unsigned char *yuv;

        x264_nal_t * nal;

} my_x264_encoder;

char *read_filename="yuv420p.yuv";

char *write_filename="encode.h264";

int main(int argc ,char **argv)

{

        int ret;

        int fd_read,fd_write;

        my_x264_encoder * encoder = (my_x264_encoder *)malloc(sizeof(my_x264_encoder));

        if(!encoder){

                printf("cannot malloc my_x264_encoder !\n");

                exit(EXIT_FAILURE);

        }

        CLEAR(*encoder);

        /****************************************************************************

         * Advanced parameter handling functions

         ****************************************************************************/

        /* These functions expose the full power of x264's preset-tune-profile system for

         * easy adjustment of large numbers //free(encoder->yuv420p_picture);of internal parameters.

         *

         * In order to replicate x264CLI's option handling, these functions MUST be called

         * in the following order:

         * 1) x264_param_default_preset

         * 2) Custom user options (via param_parse or directly assigned variables)

         * 3) x264_param_apply_fastfirstpass

         * 4) x264_param_apply_profile

         *

         * Additionally, x264CLI does not apply step 3 if the preset chosen is "placebo"

         * or --slow-firstpass is set. */

        strcpy(encoder->parameter_preset,ENCODER_PRESET);

        strcpy(encoder->parameter_tune,ENCODER_TUNE);

        encoder->x264_parameter = (x264_param_t *)malloc(sizeof(x264_param_t));

        if(!encoder->x264_parameter){

                printf("malloc x264_parameter error!\n");

                exit(EXIT_FAILURE);

        }

    /*初始化编码器*/

        CLEAR(*(encoder->x264_parameter));

        x264_param_default(encoder->x264_parameter);

        if((ret = x264_param_default_preset(encoder->x264_parameter,encoder->parameter_preset,encoder->parameter_tune))<0){

                printf("x264_param_default_preset error!\n");

                exit(EXIT_FAILURE);

        }

    /*cpuFlags 去空缓冲区继续使用不死锁保证*/

        encoder->x264_parameter->i_threads               =X264_SYNC_LOOKAHEAD_AUTO;

    /*视频选项*/

        encoder->x264_parameter->i_width                 =IMAGE_WIDTH;//要编码的图像的宽度

        encoder->x264_parameter->i_height                =IMAGE_HEIGHT;//要编码的图像的高度

        encoder->x264_parameter->i_frame_total   =0;//要编码的总帧数，不知道用0

        encoder->x264_parameter->i_keyint_max    =25;

    /*流參数*/

        encoder->x264_parameter->i_bframe        =5;

        encoder->x264_parameter->b_open_gop      =0;

        encoder->x264_parameter->i_bframe_pyramid=0;

        encoder->x264_parameter->i_bframe_adaptive=X264_B_ADAPT_TRELLIS;

    /*log參数，不须要打印编码信息时直接凝视掉*/

        encoder->x264_parameter->i_log_level    =X264_LOG_DEBUG;

        encoder->x264_parameter->i_fps_den               =1;//码率分母

        encoder->x264_parameter->i_fps_num               =25;//码率分子

        encoder->x264_parameter->b_intra_refresh =1;

        encoder->x264_parameter->b_annexb                =1;

        strcpy(encoder->parameter_profile,ENCODER_PROFILE);

        if((ret=x264_param_apply_profile(encoder->x264_parameter,encoder->parameter_profile))<0){

                printf("x264_param_apply_profile error!\n");

                exit(EXIT_FAILURE);

        }

    /*打开编码器*/

        encoder->x264_encoder = x264_encoder_open(encoder->x264_parameter);

        encoder->colorspace = ENCODER_COLORSPACE;

    /*初始化pic*/

        encoder->yuv420p_picture = (x264_picture_t *)malloc(sizeof(x264_picture_t ));

        if(!encoder->yuv420p_picture){

                printf("malloc encoder->yuv420p_picture error!\n");

                exit(EXIT_FAILURE);

        }

        if((ret = x264_picture_alloc(encoder->yuv420p_picture,encoder->colorspace,IMAGE_WIDTH,IMAGE_HEIGHT))<0){

                printf("ret=%d\n",ret);

                printf("x264_picture_alloc error!\n");

                exit(EXIT_FAILURE);

        }

        encoder->yuv420p_picture->img.i_csp = encoder->colorspace;

        encoder->yuv420p_picture->img.i_plane = 3;

        encoder->yuv420p_picture->i_type = X264_TYPE_AUTO;

    /*申请YUV buffer*/

        encoder->yuv = (uint8_t *)malloc(IMAGE_WIDTH*IMAGE_HEIGHT*3/2);

        if(!encoder->yuv){

                printf("malloc yuv error!\n");

                exit(EXIT_FAILURE);

        }

        CLEAR(*(encoder->yuv));

        encoder->yuv420p_picture->img.plane[0] = encoder->yuv;

        encoder->yuv420p_picture->img.plane[1] = encoder->yuv+IMAGE_WIDTH*IMAGE_HEIGHT;

        encoder->yuv420p_picture->img.plane[2] = encoder->yuv+IMAGE_WIDTH*IMAGE_HEIGHT+IMAGE_WIDTH*IMAGE_HEIGHT/4;

        if((fd_read = open(read_filename,O_RDONLY))<0){

                printf("cannot open input file!\n");

                exit(EXIT_FAILURE);

        }

        if((fd_write = open(write_filename,O_WRONLY | O_APPEND | O_CREAT,0777))<0){

                printf("cannot open output file!\n");

                exit(EXIT_FAILURE);

        }

        int n_nal = 0;

        x264_picture_t pic_out;

        x264_nal_t *my_nal;

        encoder->nal = (x264_nal_t *)malloc(sizeof(x264_nal_t ));

        if(!encoder->nal){

                printf("malloc x264_nal_t error!\n");

                exit(EXIT_FAILURE);

        }

        CLEAR(*(encoder->nal));

    /*编码*/

        while(read(fd_read,encoder->yuv,IMAGE_WIDTH*IMAGE_HEIGHT*3/2)>0){

                encoder->yuv420p_picture->i_pts++;

                if((ret = x264_encoder_encode(encoder->x264_encoder,&encoder->nal,&n_nal,encoder->yuv420p_picture,&pic_out))<0){

                        printf("x264_encoder_encode error!\n");

                        exit(EXIT_FAILURE);

                }

                for(my_nal = encoder->nal; my_nal<encoder->nal+n_nal; ++my_nal){

                        write(fd_write,my_nal->p_payload,my_nal->i_payload);

                }

        }

        free(encoder->yuv);

        free(encoder->yuv420p_picture);

        free(encoder->x264_parameter);

        x264_encoder_close(encoder->x264_encoder);

        free(encoder);

        close(fd_read);

        close(fd_write);

        return 0;

}

/*File : decode_h264.c

 *Auth : sjin

 *Date : 20141115

 *Mail : 413977243@qq.com

 */

/*将h264解码为yuv文件*/

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <fcntl.h>

#include <unistd.h>

#include <libavcodec/avcodec.h>

#include <libavformat/avformat.h>

#include <libavutil/mathematics.h>

#define DECODED_OUTPUT_FORMAT  AV_PIX_FMT_YUV420P

#define INPUT_FILE_NAME "encode.h264"

#define OUTPUT_FILE_NAME "decode.yuv"

/*h264文件的宽度和高度，必须和实际的宽度和高度一致

 *否则将出错

 * */

#define IMAGE_WIDTH  176

#define IMAGE_HEIGHT 144

void error_handle(const char *errorInfo )

{

	printf("%s error!\n",errorInfo);

	exit(EXIT_FAILURE);

}

int main(int argc,char ** argv)

{

	int  write_fd,ret,videoStream;

	AVFormatContext * formatContext=NULL;

	AVCodec * codec;

	AVCodecContext * codecContext;

	AVFrame * decodedFrame;

	AVPacket packet;

	uint8_t *decodedBuffer;

	unsigned int decodedBufferSize;

	int finishedFrame;

    //初始化环境

	av_register_all();

	write_fd = open(OUTPUT_FILE_NAME,O_RDWR | O_CREAT,0666);

	if(write_fd<0){

		perror("open");

		exit(1);

	}

	ret = avformat_open_input(&formatContext, INPUT_FILE_NAME, NULL,NULL);

	if(ret<0)

		error_handle("avformat_open_input error");

	ret = avformat_find_stream_info(formatContext,NULL);

	if(ret<0)

		error_handle("av_find_stream_info");

    //打印输入文件的具体信息

    av_dump_format(formatContext,0,INPUT_FILE_NAME,0);

	videoStream = 0;

	codecContext = formatContext->streams[videoStream]->codec;

	codec = avcodec_find_decoder(AV_CODEC_ID_H264);

	if(codec == NULL)

		error_handle("avcodec_find_decoder error!\n");

	ret = avcodec_open2(codecContext,codec,NULL);

	if(ret<0)

		error_handle("avcodec_open2");

    //分配保存视频帧的空间

	decodedFrame = avcodec_alloc_frame();

	if(!decodedFrame)

		error_handle("avcodec_alloc_frame!");

    //分配解码后视频帧的空间

	decodedBufferSize = avpicture_get_size(DECODED_OUTPUT_FORMAT,IMAGE_WIDTH,IMAGE_HEIGHT);

	decodedBuffer = (uint8_t *)malloc(decodedBufferSize);

	if(!decodedBuffer)

		error_handle("malloc decodedBuffer error!");

	av_init_packet(&packet);

	while(av_read_frame(formatContext,&packet)>=0){

			ret = avcodec_decode_video2(codecContext,decodedFrame,&finishedFrame,&packet);

			if(ret<0)

				error_handle("avcodec_decode_video2 error!");

			if(finishedFrame){

				avpicture_layout((AVPicture*)decodedFrame,DECODED_OUTPUT_FORMAT,IMAGE_WIDTH,IMAGE_HEIGHT,decodedBuffer,decodedBufferSize);

				ret = write(write_fd,decodedBuffer,decodedBufferSize);

				if(ret<0)

					error_handle("write yuv stream error!");

			}

		av_free_packet(&packet);

	}

    /*防止视频解码完毕后丢帧的情况*/

	while(1){

		packet.data = NULL;

		packet.size = 0;

		ret = avcodec_decode_video2(codecContext,decodedFrame,&finishedFrame,&packet);

		if(ret<=0 && (finishedFrame<=0))

			break;

		if(finishedFrame){

			avpicture_layout((AVPicture*)decodedFrame,DECODED_OUTPUT_FORMAT,IMAGE_WIDTH,IMAGE_HEIGHT,decodedBuffer,decodedBufferSize);

			ret = write(write_fd,decodedBuffer,decodedBufferSize);

			if(ret<0)

				error_handle("write yuv stream error!");

		}

		av_free_packet(&packet);

	}

	avformat_close_input(&formatContext);

	free(decodedBuffer);

	av_free(decodedFrame);

	avcodec_close(codecContext);

	return 0;

}

Makefile:

# use pkg-config for getting CFLAGS and LDLIBS

FFMPEG_LIBS=    libavdevice                        \

                libavformat                        \

                libavfilter                        \

                libavcodec                         \

                libswresample                      \

                libswscale                         \

                libavutil                          \

CFLAGS += -Wall -O2 -g

CFLAGS := $(shell pkg-config --cflags $(FFMPEG_LIBS)) $(CFLAGS)

LDLIBS := $(shell pkg-config --libs $(FFMPEG_LIBS)) $(LDLIBS)

EXAMPLES= decode_h264 yuvTO264

OBJS=$(addsuffix .o,$(EXAMPLES))

# the following examples make explicit use of the math library

LDLIBS += -lx264 -m32 -pthread -lm -ldl

.phony:all clean

all: $(OBJS) $(EXAMPLES)

clean:

	rm $(EXAMPLES) $(OBJS)

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