c++ 使用ffmpeg录制视频

使用FFmpeg库可以在C++中实现录制视频的功能。下面是一个简单的示例代码，可以录制桌面并将其保存为MP4格式的视频文件：

#include <iostream>
#include <string>
#include <sstream>
#include <ctime>
#include <chrono>
#include <thread>

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

using namespace std;

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

    // 获取当前时间作为文件名
    time_t now = time(nullptr);
    tm* localtm = localtime(&now);
    stringstream ss;
    ss << "output_" << localtm->tm_year + 1900 << "-" << localtm->tm_mon + 1 << "-" << localtm->tm_mday << "_" << localtm->tm_hour << "-" << localtm->tm_min << "-" << localtm->tm_sec << ".mp4";
    string filename = ss.str();

    // 打开视频输出文件
    AVFormatContext* outctx = nullptr;
    int ret = avformat_alloc_output_context2(&outctx, nullptr, nullptr, filename.c_str());
    if (ret < 0) {
        cerr << "Could not create output context: " << av_err2str(ret) << endl;
        return 1;
    }

    // 查找视频编码器
    AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec) {
        cerr << "Could not find encoder" << endl;
        return 1;
    }

    // 创建视频流
    AVStream* stream = avformat_new_stream(outctx, codec);
    if (!stream) {
        cerr << "Could not create stream" << endl;
        return 1;
    }

    // 配置视频编码器参数
    AVCodecContext* codecctx = avcodec_alloc_context3(codec);
    if (!codecctx) {
        cerr << "Could not allocate codec context" << endl;
        return 1;
    }
    codecctx->width = 640;
    codecctx->height = 480;
    codecctx->time_base = { 1, 25 };
    codecctx->framerate = { 25, 1 };
    codecctx->pix_fmt = AV_PIX_FMT_YUV420P;
    codecctx->gop_size = 10;
    codecctx->max_b_frames = 1;
    av_opt_set(codecctx->priv_data, "preset", "ultrafast", 0);
    av_opt_set(codecctx->priv_data, "tune", "zerolatency", 0);
    ret = avcodec_open2(codecctx, codec, nullptr);
    if (ret < 0) {
        cerr << "Could not open codec: " << av_err2str(ret) << endl;
        return 1;
    }

    // 将视频流的编码器参数复制到输出文件的视频流中
    ret = avcodec_parameters_from_context(stream->codecpar, codecctx);
    if (ret < 0) {
        cerr << "Could not copy codec parameters: " << av_err2str(ret) << endl;
        return 1;
    }

    // 打开视频输出文件
    ret = avio_open(&outctx->pb, filename.c_str(), AVIO_FLAG_WRITE);
    if (ret < 0) {
        cerr << "Could not open output file: " << av_err2str(ret) << endl;
        return 1;
    }

    // 写入输出文件的头部信息
    ret = avformat_write_header(outctx, nullptr);
    if (ret < 0) {
        cerr << "Could not write header: " << av_err2str(ret) << endl;
        return 1;
    }

    // 初始化屏幕捕获
    AVFormatContext* inctx = nullptr;
    AVDictionary* options = nullptr;
    av_dict_set(&options, "framerate", "5", 0);
    av_dict_set(&options, "offset_x", "10", 0);
    av_dict_set(&options, "offset_y", "20", 0);
    av_dict_set(&options, "video_size", "640x480", 0);
    ret = avformat_open_input(&inctx, "desktop", nullptr, &options);
    if (ret < 0) {
        cerr << "Could not open input: " << av_err2str(ret) << endl;
        return 1;
    }
    ret = avformat_find_stream_info(inctx, nullptr);
    if (ret < 0) {
        cerr << "Could not find stream info: " << av_err2str(ret) << endl;
        return 1;
    }
    AVCodec* incodec = avcodec_find_decoder(inctx->streams[0]->codecpar->codec_id);
    if (!incodec) {
        cerr << "Could not find decoder" << endl;
        return 1;
    }
    AVCodecContext* incodecctx = avcodec_alloc_context3(incodec);
    if (!incodecctx) {
        cerr << "Could not allocate codec context" << endl;
        return 1;
    }
    ret = avcodec_parameters_to_context(incodecctx, inctx->streams[0]->codecpar);
    if (ret < 0) {
        cerr << "Could not copy codec parameters: " << av_err2str(ret) << endl;
        return 1;
    }
    ret = avcodec_open2(incodecctx, incodec, nullptr);
    if (ret < 0) {
        cerr << "Could not open codec: " << av_err2str(ret) << endl;
        return 1;
    }
    AVFrame* inframe = av_frame_alloc();
    if (!inframe) {
        cerr << "Could not allocate frame" << endl;
        return 1;
    }
    AVPacket* inpacket = av_packet_alloc();
    if (!inpacket) {
        cerr << "Could not allocate packet" << endl;
        return 1;
    }

    // 初始化视频帧转换器
    SwsContext* swsctx = sws_getContext(incodecctx->width, incodecctx->height, incodecctx->pix_fmt, codecctx->width, codecctx->height, codecctx->pix_fmt, SWS_BICUBIC, nullptr, nullptr, nullptr);
    if (!swsctx) {
        cerr << "Could not create sws context" << endl;
        return 1;
    }
    AVFrame* frame = av_frame_alloc();
    if (!frame) {
        cerr << "Could not allocate frame" << endl;
        return 1;
    }
    frame->format = codecctx->pix_fmt;
    frame->width = codecctx->width;
    frame->height = codecctx->height;
    ret = av_frame_get_buffer(frame, 32);
    if (ret < 0) {
        cerr << "Could not allocate frame data: " << av_err2str(ret) << endl;
        return 1;
    }

    // 录制视频
    int64_t pts = 0;
    while (true) {
        // 从屏幕捕获中读取一帧视频
        ret = av_read_frame(inctx, inpacket);
        if (ret < 0) {
            cerr << "Could not read frame: " << av_err2str(ret) << endl;
            break;
        }
        if (inpacket->stream_index != 0) {
            av_packet_unref(inpacket);
            continue;
        }
        ret = avcodec_send_packet(incodecctx, inpacket);
        if (ret < 0) {
            cerr << "Could not send packet: " << av_err2str(ret) << endl;
            break;
        }
        while (ret >= 0) {
            ret = avcodec_receive_frame(incodecctx, inframe);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            }
            else if (ret < 0) {
                cerr << "Could not receive frame: " << av_err2str(ret) << endl;
                break;
            }

            // 将视频帧转换为输出文件的格式
            sws_scale(swsctx, inframe->data, inframe->linesize, 0, incodecctx->height, frame->data, frame->linesize);

            // 编码视频帧并写入输出文件
            frame->pts = pts++;
            ret = avcodec_send_frame(codecctx, frame);
            if (ret < 0) {
                cerr << "Could not send frame: " << av_err2str(ret) << endl;
                break;
            }
            while (ret >= 0) {
                AVPacket pkt = { 0 };
                ret = avcodec_receive_packet(codecctx, &pkt);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                }
                else if (ret < 0) {
                    cerr << "Could not receive packet: " << av_err2str(ret) << endl;
                    break;
                }
                av_packet_rescale_ts(&pkt, codecctx->time_base, stream->time_base);
                pkt.stream_index = stream->index;
                ret = av_interleaved_write_frame(outctx, &pkt);
                if (ret < 0) {
                    cerr << "Could not write frame: " << av_err2str(ret) << endl;
                    break;
                }
                av_packet_unref(&pkt);
            }
        }
        av_packet_unref(inpacket);

        // 暂停一段时间，以控制录制视频的帧率
        this_thread::sleep_for(chrono::milliseconds(200));
    }

    // 写入输出文件的尾部信息
    ret = av_write_trailer(outctx);
    if (ret < 0) {
        cerr << "Could not write trailer: " << av_err2str(ret) << endl;
        return 1;
    }

    // 释放资源
    av_frame_free(&frame);
    sws_freeContext(swsctx);
    av_packet_free(&inpacket);
    av_frame_free(&inframe);
    avcodec_free_context(&incodecctx);
    avformat_close_input(&inctx);
    avio_close(outctx->pb);
    avformat_free_context(outctx);

    return 0;
}

该示例代码使用了FFmpeg库中的AVFormatContext、AVCodecContext、AVStream、AVFrame、AVPacket等结构体和函数，实现了从屏幕捕获视频帧、转换视频帧格式、编码视频帧、写入输出文件等功能。你可以根据自己的需求修改代码中的参数和细节。