c/c++使用FFmpeg库推流本地文件，实现跳转和倍速播放的完整代码

以下是使用FFmpeg库推流本地文件，并实现跳转和倍速播放的完整代码。

#include <iostream>
#include <string>

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

using namespace std;

int main(int argc, char *argv[]) {
    if (argc < 5) {
        cerr << "Usage: " << argv[0] << " input_file output_url seek_time speed\n";
        return -1;
    }

    const char *input_file = argv[1];
    const char *output_url = argv[2];
    const double seek_time = atof(argv[3]);
    const double speed = atof(argv[4]);

    av_register_all();

    AVFormatContext *fmt_ctx = nullptr;

    if (avformat_open_input(&fmt_ctx, input_file, nullptr, nullptr) != 0) {
        cerr << "Failed to open input file" << endl;
        return -1;
    }

    if (avformat_find_stream_info(fmt_ctx, nullptr) < 0) {
        cerr << "Failed to retrieve input stream information" << endl;
        return -1;
    }

    AVStream *stream = nullptr;
    int stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &stream, 0);
    if (stream_index < 0) {
        cerr << "Failed to find video stream" << endl;
        return -1;
    }

    AVCodecParameters *codecpar = stream->codecpar;
    AVCodec *decoder = avcodec_find_decoder(codecpar->codec_id);
    if (decoder == nullptr) {
        cerr << "Failed to find decoder" << endl;
        return -1;
    }

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

    if (avcodec_open2(codec_ctx, decoder, nullptr) < 0) {
        cerr << "Failed to open codec" << endl;
        return -1;
    }

    AVFrame *frame = av_frame_alloc();
    if (frame == nullptr) {
        cerr << "Failed to allocate frame" << endl;
        return -1;
    }

    AVPacket *pkt = av_packet_alloc();
    if (pkt == nullptr) {
        cerr << "Failed to allocate packet" << endl;
        return -1;
    }

    AVDictionary *opts = nullptr;
    av_dict_set(&opts, "bufsize", "1024000", 0);
    av_dict_set(&opts, "maxrate", "1024000", 0);

    AVFormatContext *out_fmt_ctx = nullptr;
    if (avformat_alloc_output_context2(&out_fmt_ctx, nullptr, "flv", output_url) < 0) {
        cerr << "Failed to allocate output context" << endl;
        return -1;
    }

    AVStream *out_stream = avformat_new_stream(out_fmt_ctx, nullptr);
    if (out_stream == nullptr) {
        cerr << "Failed to create output stream" << endl;
        return -1;
    }

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

    if (avio_open(&out_fmt_ctx->pb, output_url, AVIO_FLAG_WRITE) < 0) {
        cerr << "Failed to open output url" << endl;
        return -1;
    }

    if (avformat_write_header(out_fmt_ctx, &opts) < 0) {
        cerr << "Failed to write output header" << endl;
        return -1;
    }

    av_dump_format(fmt_ctx, 0, input_file, 0);

    int64_t seek_target = seek_time * AV_TIME_BASE;

    if (av_seek_frame(fmt_ctx, stream_index, seek_target, AVSEEK_FLAG_BACKWARD) < 0) {
        cerr << "Failed to seek to " << seek_time << endl;
        return -1;
    }

    SwsContext *sws_ctx = sws_getContext(codec_ctx->width, codec_ctx->height, codec_ctx->pix_fmt,
                                         codec_ctx->width, codec_ctx->height, AV_PIX_FMT_YUV420P, 0, nullptr, nullptr, nullptr);
    if (sws_ctx == nullptr) {
        cerr << "Failed to allocate sws context" << endl;
        return -1;
    }

    AVRational frame_rate = stream->r_frame_rate;
    AVRational time_base = stream->time_base;
    AVRational out_time_base = out_stream->time_base;

    int64_t next_pts = 0;
    double speed_factor = 1.0 / speed;

    while (av_read_frame(fmt_ctx, pkt) >= 0) {
        if (pkt->stream_index != stream_index) {
            av_packet_unref(pkt);
            continue;
        }

        if (avcodec_send_packet(codec_ctx, pkt) < 0) {
            cerr << "Failed to send packet to decoder" << endl;
            return -1;
        }

        while (avcodec_receive_frame(codec_ctx, frame) == 0) {
            double pts = static_cast<double>(frame->pts) * time_base.num / time_base.den;
            double dts = static_cast<double>(frame->pkt_dts) * time_base.num / time_base.den;
            double duration = static_cast<double>(frame->pkt_duration) * time_base.num / time_base.den;

            if (pts < seek_time) {
                av_frame_unref(frame);
                continue;
            }

            if (duration > 0) {
                duration *= speed_factor;
                frame->pkt_duration = static_cast<int64_t>(duration * time_base.den / time_base.num);
            }

            if (pts >= next_pts) {
                int64_t pts_ms = static_cast<int64_t>(pts * 1000);
                int64_t out_pts = av_rescale_q(pts_ms, {1, 1000}, out_time_base);
                int64_t delay_ms = static_cast<int64_t>((pts - next_pts) * 1000 * speed_factor);
                int64_t delay = av_rescale_q(delay_ms, {1, 1000}, out_time_base);

                av_usleep(delay);

                AVFrame *out_frame = av_frame_alloc();
                if (out_frame == nullptr) {
                    cerr << "Failed to allocate output frame" << endl;
                    return -1;
                }

                out_frame->format = AV_PIX_FMT_YUV420P;
                out_frame->width = codec_ctx->width;
                out_frame->height = codec_ctx->height;
                av_frame_get_buffer(out_frame, 0);

                sws_scale(sws_ctx, frame->data, frame->linesize, 0, codec_ctx->height, out_frame->data, out_frame->linesize);

                out_frame->pts = out_pts;

                if (avcodec_send_frame(out_stream->codec, out_frame) < 0) {
                    cerr << "Failed to send frame to encoder" << endl;
                    return -1;
                }

                while (avcodec_receive_packet(out_stream->codec, pkt) == 0) {
                    pkt->stream_index = out_stream->index;
                    av_interleaved_write_frame(out_fmt_ctx, pkt);

                    av_packet_unref(pkt);
                }

                av_frame_unref(out_frame);

                next_pts += static_cast<int64_t>(duration * AV_TIME_BASE);
            }

            av_frame_unref(frame);
        }

        av_packet_unref(pkt);
    }

    av_write_trailer(out_fmt_ctx);

    av_packet_free(&pkt);
    av_frame_free(&frame);
    avcodec_free_context(&codec_ctx);
    avformat_close_input(&fmt_ctx);

    avio_closep(&out_fmt_ctx->pb);
    avformat_free_context(out_fmt_ctx);

    sws_freeContext(sws_ctx);

    return 0;
}

使用方法：

./push_stream input_file output_url seek_time speed

其中，`input_file` 是输入的本地文件名，`output_url` 是输出的推流地址，`seek_time` 是跳转的时间（单位秒），`speed` 是倍速播放的速度。例如：

./push_stream input.mp4 rtmp://127.0.0.1/live/test 30 2.0

表示将 `input.mp4` 推流到 `rtmp://127.0.0.1/live/test`，从第 30 秒开始播放，以两倍速度播放。