ffmpeg打开摄像头 c++

要在 C++ 中使用 FFmpeg 打开摄像头，你可以使用 FFmpeg 的 libavformat 库和 libavcodec 库。

以下是一个简单的示例程序，它使用 FFmpeg 打开摄像头并将视频流保存为 AVI 文件：

#include <iostream>
extern "C" {
    #include <libavformat/avformat.h>
    #include <libavcodec/avcodec.h>
}
using namespace std;

int main(int argc, char** argv) {
    av_register_all();
    avformat_network_init();

    AVFormatContext* pFormatCtx = avformat_alloc_context();
    AVDictionary* options = NULL;
    av_dict_set(&options, "video_size", "640x480", 0);
    av_dict_set(&options, "framerate", "30", 0);

    AVInputFormat* pInputFmt = av_find_input_format("v4l2");
    if (avformat_open_input(&pFormatCtx, "/dev/video0", pInputFmt, &options) != 0) {
        cerr << "Could not open input stream" << endl;
        return -1;
    }

    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        cerr << "Could not find stream information" << endl;
        return -1;
    }

    AVCodec* pCodec = NULL;
    AVCodecParameters* pCodecParameters = NULL;
    int videoStreamIndex = -1;

    for (unsigned int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStreamIndex = i;
            pCodecParameters = pFormatCtx->streams[i]->codecpar;
            pCodec = avcodec_find_decoder(pCodecParameters->codec_id);
            break;
        }
    }

    if (videoStreamIndex == -1 || pCodec == NULL) {
        cerr << "Could not find video stream or codec" << endl;
        return -1;
    }

    AVCodecContext* pCodecCtx = avcodec_alloc_context3(pCodec);
    if (avcodec_parameters_to_context(pCodecCtx, pCodecParameters) < 0) {
        cerr << "Failed to copy codec parameters to decoder context" << endl;
        return -1;
    }

    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        cerr << "Failed to open codec" << endl;
        return -1;
    }

    AVFrame* pFrame = av_frame_alloc();
    AVPacket packet;

    av_init_packet(&packet);
    packet.data = NULL;
    packet.size = 0;

    AVFormatContext* pOutputFormatCtx = NULL;
    avformat_alloc_output_context2(&pOutputFormatCtx, NULL, NULL, "output.avi");
    if (!pOutputFormatCtx) {
        cerr << "Could not create output context" << endl;
        return -1;
    }
    AVOutputFormat* pOutputFmt = pOutputFormatCtx->oformat;

    AVStream* pOutputStream = avformat_new_stream(pOutputFormatCtx, NULL);
    if (!pOutputStream) {
        cerr << "Could not create output stream" << endl;
        return -1;
    }

    if (avcodec_parameters_copy(pOutputStream->codecpar, pCodecParameters) < 0) {
        cerr << "Failed to copy codec parameters to output stream" << endl;
        return -1;
    }
    pOutputStream->codecpar->codec_tag = 0;

    if (!(pOutputFmt->flags & AVFMT_NOFILE)) {
        if (avio_open(&pOutputFormatCtx->pb, "output.avi", AVIO_FLAG_WRITE) < 0) {
            cerr << "Could not open output file" << endl;
            return -1;
        }
    }

    if (avformat_write_header(pOutputFormatCtx, NULL) < 0) {
        cerr << "Error occurred when opening output file" << endl;
        return -1;
    }

    while (av_read_frame(pFormatCtx, &packet) >= 0) {
        if (packet.stream_index == videoStreamIndex) {
            int ret = avcodec_send_packet(pCodecCtx, &packet);
            if (ret < 0) {
                cerr << "Error sending packet to decoder" << endl;
                break;
            }
            while (ret >= 0) {
                ret = avcodec_receive_frame(pCodecCtx, pFrame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    cerr << "Error during decoding" << endl;
                    return -1;
                }
                if (ret >= 0) {
                    AVPacket newPacket;
                    av_init_packet(&newPacket);
                    newPacket.data = NULL;
                    newPacket.size = 0;

                    if (avcodec_send_frame(pOutputStream->codec, pFrame) >= 0) {
                        while (avcodec_receive_packet(pOutputStream->codec, &newPacket) >= 0) {
                            av_interleaved_write_frame(pOutputFormatCtx, &newPacket);
                            av_packet_unref(&newPacket);
                        }
                    }
                }
            }
        }
        av_packet_unref(&packet);
    }

    av_write_trailer(pOutputFormatCtx);

    avcodec_free_context(&pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}

在这个例子中，我们首先初始化 FFmpeg 库并打开摄像头。然后，我们查找视频流的索引和解码器，并初始化解码器上下文。接下来，我们循环读取视频帧并将它们解码到 AVFrame 中。最后，我们将解码后的帧编码为 AVPacket 并写入 AVI 文件中。

请注意，这只是一个简单的示例程序，可能需要进行修改以适应不同的使用情况。