c++ ffmpeg 取一帧存为jgp

以下是使用C++和FFmpeg将一帧YUV数据保存为JPEG图片的示例代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <fstream>

extern "C" {
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}

void save_frame_as_jpeg(uint8_t* frame_data, int width, int height, const char* output_filename) {
    AVCodec* codec;
    AVCodecContext* codec_context;
    AVFrame* frame;
    AVPacket packet;
    struct SwsContext* sws_context;

    av_register_all();

    // 初始化输入帧
    frame = av_frame_alloc();
    frame->width = width;
    frame->height = height;
    frame->format = AV_PIX_FMT_YUV420P;

    // 分配缓冲区
    int buffer_size = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, width, height, 1);
    uint8_t* buffer = (uint8_t*)av_malloc(buffer_size);
    av_image_fill_arrays(frame->data, frame->linesize, buffer, AV_PIX_FMT_YUV420P, width, height, 1);

    // 将YUV数据复制到输入帧
    int y_size = width * height;
    memcpy(frame->data[0], frame_data, y_size); // Y
    memcpy(frame->data[1], frame_data + y_size, y_size / 4); // U
    memcpy(frame->data[2], frame_data + y_size + y_size / 4, y_size / 4); // V

    // 初始化输出文件
    AVFormatContext* format_context = nullptr;
    avformat_alloc_output_context2(&format_context, nullptr, nullptr, output_filename);
    if (!format_context) {
        std::cerr << "Failed to allocate output format context" << std::endl;
        return;
    }

    // 查找JPEG编码器
    codec = avcodec_find_encoder(AV_CODEC_ID_MJPEG);
    if (!codec) {
        std::cerr << "Failed to find JPEG encoder" << std::endl;
        return;
    }

    // 初始化编码器上下文
    codec_context = avcodec_alloc_context3(codec);
    codec_context->pix_fmt = AV_PIX_FMT_YUVJ420P;
    codec_context->width = width;
    codec_context->height = height;
    codec_context->time_base = {1, 25}; // 假设帧率为25fps

    // 打开编码器
    if (avcodec_open2(codec_context, codec, nullptr) < 0) {
        std::cerr << "Failed to open JPEG encoder" << std::endl;
        return;
    }

    // 创建输出流
    AVStream* stream = avformat_new_stream(format_context, codec);
    if (!stream) {
        std::cerr << "Failed to create output stream" << std::endl;
        return;
    }

    // 将编码器上下文复制到输出流
    avcodec_parameters_from_context(stream->codecpar, codec_context);

    // 打开输出文件
    if (avio_open(&format_context->pb, output_filename, AVIO_FLAG_WRITE) < 0) {
        std::cerr << "Failed to open output file" << std::endl;
        return;
    }

    // 写入文件头
    avformat_write_header(format_context, nullptr);

    // 初始化SWS上下文
    sws_context = sws_getContext(width, height, AV_PIX_FMT_YUV420P, width, height, AV_PIX_FMT_YUVJ420P, 0, nullptr, nullptr, nullptr);
    if (!sws_context) {
        std::cerr << "Failed to initialize SWS context" << std::endl;
        return;
    }

    // 将输入帧转换为输出帧
    AVFrame* output_frame = av_frame_alloc();
    output_frame->width = width;
    output_frame->height = height;
    output_frame->format = AV_PIX_FMT_YUVJ420P;
    av_image_fill_arrays(output_frame->data, output_frame->linesize, nullptr, AV_PIX_FMT_YUVJ420P, width, height, 1);
    sws_scale(sws_context, frame->data, frame->linesize, 0, height, output_frame->data, output_frame->linesize);

    // 编码并写入输出文件
    av_init_packet(&packet);
    packet.data = nullptr;
    packet.size = 0;
    avcodec_send_frame(codec_context, output_frame);
    while (avcodec_receive_packet(codec_context, &packet) == 0) {
        av_write_frame(format_context, &packet);
        av_packet_unref(&packet);
    }

    // 写入文件尾
    av_write_trailer(format_context);

    // 清理资源
    av_frame_free(&frame);
    av_frame_free(&output_frame);
    avcodec_free_context(&codec_context);
    avformat_free_context(format_context);
    av_free(buffer);
    sws_freeContext(sws_context);
}

int main() {
    // 假设已经获取到一帧YUV数据，存储在frame_data中
    uint8_t* frame_data = nullptr;
    int width = 640;
    int height = 480;

    // 保存为JPEG图片
    save_frame_as_jpeg(frame_data, width, height, "output.jpg");

    return 0;
}