找到H264编码器 然后创建输出流 然后创建编码器上下文，设置编码器参数 打开编码器

好的，以下是用FFmpeg库实现的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavutil/imgutils.h>

int main(int argc, char *argv[])
{
    AVCodec *codec;
    AVCodecContext *codec_ctx;
    AVFrame *frame;
    AVPacket pkt;
    int ret, i, j, k;
    int width = 640, height = 480;
    int bitrate = 1000000;
    int fps = 25;
    int gop_size = 10;
    int max_b_frames = 0;
    char *output_file = "output.h264";
    FILE *output_fp;

    avcodec_register_all();

    codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        return -1;
    }

    codec_ctx = avcodec_alloc_context3(codec);

    codec_ctx->bit_rate = bitrate;
    codec_ctx->width = width;
    codec_ctx->height = height;
    codec_ctx->time_base = (AVRational){1, fps};
    codec_ctx->gop_size = gop_size;
    codec_ctx->max_b_frames = max_b_frames;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;

    if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
        fprintf(stderr, "Failed to open codec\n");
        return -1;
    }

    frame = av_frame_alloc();
    frame->format = codec_ctx->pix_fmt;
    frame->width = codec_ctx->width;
    frame->height = codec_ctx->height;

    ret = av_frame_get_buffer(frame, 32);
    if (ret < 0) {
        fprintf(stderr, "Failed to allocate picture\n");
        return -1;
    }

    output_fp = fopen(output_file, "wb");
    if (!output_fp) {
        fprintf(stderr, "Failed to open output file\n");
        return -1;
    }

    for (i = 0; i < 100; i++) {
        av_init_packet(&pkt);
        pkt.data = NULL;
        pkt.size = 0;

        ret = av_frame_make_writable(frame);
        if (ret < 0) {
            fprintf(stderr, "Failed to make frame writable\n");
            break;
        }

        for (j = 0; j < height; j++) {
            for (k = 0; k < width; k++) {
                frame->data[0][j * frame->linesize[0] + k] = j + i * 3;
            }
        }

        for (j = 0; j < height / 2; j++) {
            for (k = 0; k < width / 2; k++) {
                frame->data[1][j * frame->linesize[1] + k] = 128 + j + i * 2;
                frame->data[2][j * frame->linesize[2] + k] = 64 + k + i * 5;
            }
        }

        frame->pts = i;

        ret = avcodec_send_frame(codec_ctx, frame);
        if (ret < 0) {
            fprintf(stderr, "Failed to send frame\n");
            break;
        }

        while (ret >= 0) {
            ret = avcodec_receive_packet(codec_ctx, &pkt);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            } else if (ret < 0) {
                fprintf(stderr, "Failed to receive packet\n");
                break;
            }

            fwrite(pkt.data, 1, pkt.size, output_fp);
            av_packet_unref(&pkt);
        }
    }

    avcodec_send_frame(codec_ctx, NULL);

    while (ret >= 0) {
        ret = avcodec_receive_packet(codec_ctx, &pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            break;
        } else if (ret < 0) {
            fprintf(stderr, "Failed to receive packet\n");
            break;
        }

        fwrite(pkt.data, 1, pkt.size, output_fp);
        av_packet_unref(&pkt);
    }

    fclose(output_fp);

    av_frame_free(&frame);
    avcodec_free_context(&codec_ctx);

    return 0;
}

以上代码实现了以下功能：

1. 找到H264编码器
2. 创建编码器上下文，设置编码器参数
3. 打开编码器
4. 创建输出文件
5. 循环编码并输出到文件
6. 关闭编码器和输出文件

你可以根据自己的需要修改代码中的参数和输入数据来进行测试。