利用x264的库，以下代码可实现将YUV420P的yuv文件编码为264文件。

#include "stdafx.h"
#include <Windows.h>

#include "stdint.h"

#ifdef __cplusplus
extern "C"
{
    #include "x264.h"
};
#else
    #include "x264.h"
#endif

int _tmain(int argc, _TCHAR* argv[])
{
    SYSTEMTIME st;
    GetLocalTime(&st);

    char szYUVFile[256] = {0};
    char sz264File[256] = {0};

    sprintf(szYUVFile, ".\\sample_640x360_yuv420p.yuv");
    sprintf(sz264File, ".\\output_%04d%02d%02d_%02d%02d%02d.264", 
            st.wYear, st.wMonth, st.wDay, st.wHour, st.wMinute, st.wSecond);

    FILE *fpYUV = fopen(szYUVFile, "rb");
    if (!fpYUV)
    {
        printf("fopen %s fail.\n", szYUVFile);
        return -1;
    }

    FILE *fp264 = fopen(sz264File, "wb");
    if (!fp264)
    {
        printf("fopen %s fail.\n", sz264File);
        return -1;
    }

    int nWidth  = 640;
    int nHeight = 360;

    x264_picture_t pic;
    x264_picture_t pic_out;

    x264_picture_init(&pic);

    int nRet = x264_picture_alloc(&pic, X264_CSP_I420, nWidth, nHeight);
    if (nRet < 0)
    {
        printf("x264_picture_alloc fail\n");
        return -1;
    }

    /*x264_param_t default_264_param;
    x264_param_default(&default_264_param);*/

    x264_param_t param;

    /* Get default params for preset/tuning */
    if( x264_param_default_preset( &param, "medium", NULL ) < 0 )
    {
        printf("x264_param_default_preset fail. \n");

        return -1;
    }

    /* Configure non-default params */
    //param.i_bitdepth  = 8;
    param.i_csp            = X264_CSP_I420;
    param.i_width          = nWidth;
    param.i_height         = nHeight;
    param.b_vfr_input      = 0;
    param.b_repeat_headers = 1;
    param.b_annexb         = 1;

    /* Apply profile restrictions. */
    if( x264_param_apply_profile( &param, "high" ) < 0 )
    {
        printf("x264_param_apply_profile fail. \n");
        return -1;
    }

    int luma_size   = nWidth * nHeight;
    int chroma_size = luma_size / 4;

    x264_t     *p264_t = NULL;
    x264_nal_t *pnal_t = NULL;
    int        iNAL    = 0;

    int i_frame = 0;
    int i_frame_size;

    // 打开编码器
    p264_t = x264_encoder_open(&param);
    if (NULL == p264_t)
    {
        printf("x264_encoder_open fail.\n");
        return -1;
    }

    // 返回SPS PPS信息
    /*int nNALsInBytes = x264_encoder_headers(p264_t, &pnal_t, &iNAL);
    if (nNALsInBytes < 0)
    {
    printf("x264_encoder_headers fail. \m");
    return -1;
    }*/

    x264_nal_t *nal;
    int i_nal;

    /* Encode frames */
    for( ;; i_frame++ )
    {
        /* Read input frame */
        if( fread( pic.img.plane[0], 1, luma_size, fpYUV ) != luma_size )
        {
            break;
        }

        if( fread( pic.img.plane[1], 1, chroma_size, fpYUV ) != chroma_size )
        {
            break;
        }

        if( fread( pic.img.plane[2], 1, chroma_size, fpYUV ) != chroma_size )
        {
            break;
        }

        pic.i_pts = i_frame;
        i_frame_size = x264_encoder_encode( p264_t, &nal, &i_nal, &pic, &pic_out );
        if( i_frame_size < 0 )
        {
            break;
        }

        if (i_frame_size > 0)
        {
            if( !fwrite( nal->p_payload, i_frame_size, 1, fp264 ) )
            {
                return -1;
            }
        }
    }

    /* Flush delayed frames */
    while( x264_encoder_delayed_frames( p264_t ) )
    {
        i_frame_size = x264_encoder_encode( p264_t, &nal, &i_nal, NULL, &pic_out );
        if( i_frame_size < 0 )
        {
            break;
        }

        if (i_frame_size > 0)
        {
            if( !fwrite( nal->p_payload, i_frame_size, 1, fp264 ) )
            {
                return -1;
            }
        }
    }

    // 关闭编码器
    x264_encoder_close(p264_t);
    x264_picture_clean(&pic);

    if (fpYUV)
    {
        fclose(fpYUV);
        fpYUV = NULL;
    }
    
    if (fp264)
    {
        fclose(fp264);
        fp264 = NULL;
    }

    getchar();

    return 0;
} 

References:

https://github.com/leixiaohua1020/simplest_encoder/tree/master/simplest_x264_encoder
x264官方提供的example.c