ffmpeg 解码rtsp

可以使用 ffmpeg 库来解码 RTSP 视频流。下面是一个简单的 C++ 代码示例，使用 ffmpeg 库解码 RTSP 视频流：

#include <iostream>
#include <thread>
#include <chrono>

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

int main(int argc, char *argv[]) {
    AVFormatContext *pFormatCtx = nullptr;
    AVCodecContext *pCodecCtxOrig = nullptr;
    AVCodecContext *pCodecCtx = nullptr;
    AVCodec *pCodec = nullptr;
    AVFrame *pFrame = nullptr;
    AVPacket *packet = nullptr;

    // RTSP URL
    const char *url = "rtsp://example.com/stream";

    // Register all formats and codecs
    av_register_all();
    avformat_network_init();

    // Open RTSP stream
    if (avformat_open_input(&pFormatCtx, url, nullptr, nullptr) != 0) {
        std::cerr << "Could not open input stream" << std::endl;
        return -1;
    }

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, nullptr) < 0) {
        std::cerr << "Could not find stream information" << std::endl;
        return -1;
    }

    // Find the first video stream
    int videoStreamIndex = -1;
    for (int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStreamIndex = i;
            break;
        }
    }

    // Check if video stream was found
    if (videoStreamIndex == -1) {
        std::cerr << "Could not find video stream" << std::endl;
        return -1;
    }

    // Get a pointer to the codec context for the video stream
    pCodecCtxOrig = pFormatCtx->streams[videoStreamIndex]->codec;

    // Find the decoder for the video stream codec
    pCodec = avcodec_find_decoder(pCodecCtxOrig->codec_id);
    if (!pCodec) {
        std::cerr << "Unsupported codec" << std::endl;
        return -1;
    }

    // Copy context
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0) {
        std::cerr << "Could not copy codec context" << std::endl;
        return -1;
    }

    // Open codec
    if (avcodec_open2(pCodecCtx, pCodec, nullptr) < 0) {
        std::cerr << "Could not open codec" << std::endl;
        return -1;
    }

    // Allocate video frame
    pFrame = av_frame_alloc();

    // Allocate packet
    packet = av_packet_alloc();

    // Read frames from the stream
    while (av_read_frame(pFormatCtx, packet) >= 0) {
        // Check if packet belongs to video stream
        if (packet->stream_index == videoStreamIndex) {
            // Send packet to decoder
            avcodec_send_packet(pCodecCtx, packet);

            // Receive decoded frame
            int ret = avcodec_receive_frame(pCodecCtx, pFrame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                // Not enough data yet, or end of file
                continue;
            } else if (ret < 0) {
                std::cerr << "Error decoding frame" << std::endl;
                break;
            }

            // Convert frame to RGB
            SwsContext *sws_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                                                 pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_RGB24,
                                                 SWS_BILINEAR, nullptr, nullptr, nullptr);
            if (!sws_ctx) {
                std::cerr << "Could not initialize the conversion context" << std::endl;
                break;
            }

            AVFrame *rgbFrame = av_frame_alloc();
            if (!rgbFrame) {
                std::cerr << "Could not allocate RGB frame" << std::endl;
                break;
            }

            av_image_alloc(rgbFrame->data, rgbFrame->linesize, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_RGB24, 1);

            sws_scale(sws_ctx, (const uint8_t *const *) pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
                      rgbFrame->data, rgbFrame->linesize);

            // Display frame
            std::cout << "Frame width: " << pCodecCtx->width << ", height: " << pCodecCtx->height << std::endl;

            // Free RGB frame
            av_freep(&rgbFrame->data[0]);
            av_frame_free(&rgbFrame);
            sws_freeContext(sws_ctx);
        }

        // Free packet
        av_packet_unref(packet);

        // Sleep for a short time to simulate real-time playback
        std::this_thread::sleep_for(std::chrono::milliseconds(33));
    }

    // Free resources
    av_packet_free(&packet);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avcodec_free_context(&pCodecCtx);
    avformat_close_input(&pFormatCtx);
    avformat_network_deinit();

    return 0;
}

这个代码示例使用了 ffmpeg 库中的 AVFormatContext、AVCodecContext、AVCodec、AVFrame 和 AVPacket 等数据类型，以及相关的函数来打开 RTSP 视频流，解码视频帧，并展示出来。这个代码示例中，我们将解码出来的视频帧转换为 RGB 格式，并输出帧的宽度和高度。你可以根据自己的需求来修改这个代码示例。