Qt音视频开发05-保存视频文件（yuv/h264/mp4）

可以使用FFmpeg库来保存视频文件，具体实现可以参考以下代码：

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <chrono>
#include <thread>
#include <opencv2/opencv.hpp>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/imgutils.h>
#include <libswscale/swscale.h>

using namespace std;
using namespace cv;

int main(int argc, char* argv[])
{
    // 初始化FFmpeg库
    av_register_all();
    avcodec_register_all();

    // 打开视频文件
    string filename = "test.mp4";
    AVFormatContext* format_ctx = nullptr;
    if (avformat_open_input(&format_ctx, filename.c_str(), nullptr, nullptr) != 0) {
        cerr << "Failed to open video file " << filename << endl;
        return -1;
    }

    // 查找视频流
    int video_stream_index = -1;
    for (unsigned int i = 0; i < format_ctx->nb_streams; i++) {
        if (format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_index = i;
            break;
        }
    }
    if (video_stream_index == -1) {
        cerr << "Failed to find video stream in " << filename << endl;
        avformat_close_input(&format_ctx);
        return -1;
    }

    // 获取视频流的解码器
    AVCodec* codec = avcodec_find_decoder(format_ctx->streams[video_stream_index]->codecpar->codec_id);
    if (codec == nullptr) {
        cerr << "Failed to find codec for video stream in " << filename << endl;
        avformat_close_input(&format_ctx);
        return -1;
    }

    // 打开解码器
    AVCodecContext* codec_ctx = avcodec_alloc_context3(codec);
    if (avcodec_parameters_to_context(codec_ctx, format_ctx->streams[video_stream_index]->codecpar) != 0) {
        cerr << "Failed to copy codec parameters to decoder context in " << filename << endl;
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
    if (avcodec_open2(codec_ctx, codec, nullptr) != 0) {
        cerr << "Failed to open codec for video stream in " << filename << endl;
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }

    // 创建视频文件
    string output_filename = "output.mp4";
    AVFormatContext* output_format_ctx = nullptr;
    if (avformat_alloc_output_context2(&output_format_ctx, nullptr, nullptr, output_filename.c_str()) != 0) {
        cerr << "Failed to create output format context for " << output_filename << endl;
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }

    // 添加视频流
    AVStream* output_stream = avformat_new_stream(output_format_ctx, nullptr);
    if (output_stream == nullptr) {
        cerr << "Failed to create output video stream for " << output_filename << endl;
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        avformat_free_context(output_format_ctx);
        return -1;
    }
    output_stream->id = output_format_ctx->nb_streams - 1;
    if (avcodec_parameters_copy(output_stream->codecpar, format_ctx->streams[video_stream_index]->codecpar) != 0) {
        cerr << "Failed to copy codec parameters to output video stream in " << output_filename << endl;
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        avformat_free_context(output_format_ctx);
        return -1;
    }
    output_stream->codecpar->codec_tag = 0;
    if (avformat_write_header(output_format_ctx, nullptr) != 0) {
        cerr << "Failed to write output file header for " << output_filename << endl;
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        avformat_free_context(output_format_ctx);
        return -1;
    }

    // 分配解码缓存
    AVFrame* frame = av_frame_alloc();
    AVPacket packet;
    av_init_packet(&packet);

    // 读取视频帧并保存
    while (av_read_frame(format_ctx, &packet) == 0) {
        if (packet.stream_index == video_stream_index) {
            if (avcodec_send_packet(codec_ctx, &packet) != 0) {
                cerr << "Failed to send packet to decoder in " << filename << endl;
                break;
            }
            while (avcodec_receive_frame(codec_ctx, frame) == 0) {
                // 将YUV图像转换为BGR图像
                Mat bgr_image(frame->height, frame->width, CV_8UC3);
                SwsContext* sws_ctx = sws_getContext(frame->width, frame->height, (AVPixelFormat)frame->format,
                                                     frame->width, frame->height, AV_PIX_FMT_BGR24,
                                                     SWS_BILINEAR, nullptr, nullptr, nullptr);
                uint8_t* data[AV_NUM_DATA_POINTERS] = { 0 };
                data[0] = bgr_image.data;
                int linesize[AV_NUM_DATA_POINTERS] = { 0 };
                linesize[0] = bgr_image.step;
                sws_scale(sws_ctx, frame->data, frame->linesize, 0, frame->height, data, linesize);
                sws_freeContext(sws_ctx);

                // 保存BGR图像
                AVPacket output_packet;
                av_init_packet(&output_packet);
                output_packet.data = nullptr;
                output_packet.size = 0;
                avcodec_send_frame(codec_ctx, frame);
                while (avcodec_receive_packet(codec_ctx, &output_packet) == 0) {
                    output_packet.stream_index = output_stream->id;
                    av_write_frame(output_format_ctx, &output_packet);
                    av_packet_unref(&output_packet);
                }

                // 显示BGR图像
                imshow("BGR Image", bgr_image);
                waitKey(1);
            }
        }
        av_packet_unref(&packet);
    }

    // 释放资源
    av_write_trailer(output_format_ctx);
    avcodec_free_context(&codec_ctx);
    avformat_close_input(&format_ctx);
    avformat_free_context(output_format_ctx);
    av_frame_free(&frame);
    return 0;
}

这段代码可以读取一个视频文件，将其中的每一帧转换为BGR格式的图像，并保存为另一个视频文件。其中，使用了OpenCV库来显示BGR图像，使用了FFmpeg库来读取和保存视频文件。