[OpenCV+FFMepg]使用FFMepg编码cv::Mat并写入视频

2024-07-01 08:31| 来源: 网络整理| 查看: 265

OpenCV本身就已经包含很多视频读写的基础能力，但是如果需要更全面的音视频编解码的能力，目前最通用的跨平台方案就是OpenCV+FFMpeg，以下就来介绍如何透过FFMpeg对cv::Mat进行编码，并写入到文件中。

首先，需要引入一些必要头文件，注意FFMpeg的header在C++中引入需要加入extern "C"

#include #include #include #include #include extern "C" { #include #include #include #include #include #include }

接著创建一个方法，如下

int writeVideo(const std::string& video_path, std::vector& frames, int width, int height, int fps);

首先需要指定编码的格式，这里以MP4为例，可以根据需求修改

const AVCodec* videoCodec = avcodec_find_encoder(AV_CODEC_ID_MPEG4); AVCodecContext* videoCodecContext = avcodec_alloc_context3(videoCodec); if (!videoCodecContext) { std::cerr width = width; videoCodecContext->height = height; //videoCodecContext->time_base = (AVRational){ 1, fps }; //error C4576: a parenthesized type followed by an initializer list is a non-standard explicit type conversion syntax //videoCodecContext->framerate = (AVRational){ fps, 1 }; videoCodecContext->time_base.num = 1; videoCodecContext->time_base.den = fps; videoCodecContext->framerate.num = fps; videoCodecContext->framerate.den = 1; videoCodecContext->gop_size = 12; videoCodecContext->max_b_frames = 0; videoCodecContext->pix_fmt = AV_PIX_FMT_YUV420P; if (formatContext->oformat->flags & AVFMT_GLOBALHEADER) { videoCodecContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER; }

Encoder的参数可以透过这样设置，详细的介绍可以参考这里

// 设置encoder参数 AVDictionary *param = 0; av_dict_set(¶m, "preset", "medium", 0); av_dict_set(¶m, "tune", "zerolatency", 0); //开启Codec并写入设置 error = avcodec_open2(videoCodecContext, videoCodec, ¶m);

接著就可以开始循环写入cv::Mat

for (const cv::Mat& frame : frames) { // convert the cv::Mat to an AVFrame AVFrame* avFrame = av_frame_alloc(); avFrame->format = videoCodecContext->pix_fmt; avFrame->width = width; avFrame->height = height; error = av_frame_get_buffer(avFrame, 0); checkError(error, "Error allocating frame buffer"); struct SwsContext* frameConverter = sws_getContext(width, height, AV_PIX_FMT_BGR24, width, height, videoCodecContext->pix_fmt, SWS_BICUBIC, nullptr, nullptr, nullptr); uint8_t* srcData[AV_NUM_DATA_POINTERS] = { frame.data }; int srcLinesize[AV_NUM_DATA_POINTERS] = { static_cast(frame.step) }; sws_scale(frameConverter, srcData, srcLinesize, 0, height, avFrame->data, avFrame->linesize); sws_freeContext(frameConverter); ... }

底下附上完整代码

#include #include #include #include #include extern "C" { #include #include #include #include #include #include } // helper function to check for FFmpeg errors inline void checkError(int error, const std::string& message) { if (error < 0) { //std::cerr pix_fmt = AV_PIX_FMT_YUV420P; if (formatContext->oformat->flags & AVFMT_GLOBALHEADER) { videoCodecContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER; } // 设置encoder参数 AVDictionary *param = 0; av_dict_set(¶m, "preset", "medium", 0); av_dict_set(¶m, "tune", "zerolatency", 0); error = avcodec_open2(videoCodecContext, videoCodec, ¶m); checkError(error, "Error opening"); error = avcodec_parameters_from_context(videoStream->codecpar, videoCodecContext); checkError(error, "Error setting video codec parameters"); // open the output file error = avio_open(&formatContext->pb, video_path.c_str(), AVIO_FLAG_WRITE); checkError(error, "Error opening output file"); // write the video file header error = avformat_write_header(formatContext, nullptr); checkError(error, "Error writing video file header"); AVPacket* packet = av_packet_alloc(); if (!packet) { std::cerr pix_fmt; avFrame->width = width; avFrame->height = height; error = av_frame_get_buffer(avFrame, 0); checkError(error, "Error allocating frame buffer"); struct SwsContext* frameConverter = sws_getContext(width, height, AV_PIX_FMT_BGR24, width, height, videoCodecContext->pix_fmt, SWS_BICUBIC, nullptr, nullptr, nullptr); uint8_t* srcData[AV_NUM_DATA_POINTERS] = { frame.data }; int srcLinesize[AV_NUM_DATA_POINTERS] = { static_cast(frame.step) }; sws_scale(frameConverter, srcData, srcLinesize, 0, height, avFrame->data, avFrame->linesize); sws_freeContext(frameConverter); // encode the AVFrame // avFrame->pts = packet->pts; avFrame->pts=frame_count*(videoStream->time_base.den)/((videoStream->time_base.num)*fps); frame_count += 1; error = avcodec_send_frame(videoCodecContext, avFrame); checkError(error, "Error sending frame to video codec"); while (error >= 0) { error = avcodec_receive_packet(videoCodecContext, packet); if (error == AVERROR(EAGAIN) || error == AVERROR_EOF) { break; } checkError(error, "Error encoding video frame"); // write the encoded packet to the output file packet->stream_index = videoStream->index; error = av_interleaved_write_frame(formatContext, packet); checkError(error, "Error writing video packet"); av_packet_unref(packet); } av_frame_free(&avFrame); } // flush the rest of the packets int ret = 0; avcodec_send_frame(videoCodecContext, nullptr); do { av_packet_unref(packet); ret = avcodec_receive_packet(videoCodecContext, packet); if (!ret) { error = av_interleaved_write_frame(formatContext, packet); checkError(error, "Error writing video packet"); } } while (!ret); av_write_trailer(formatContext); avformat_close_input(&formatContext); // clean up av_packet_free(&packet); avcodec_free_context(&videoCodecContext); avformat_free_context(formatContext); avformat_network_deinit(); return EXIT_SUCCESS; } std::vector readVideo(const std::string video_path) { // initialize FFmpeg av_log_set_level(AV_LOG_ERROR); avformat_network_init(); AVFormatContext* formatContext = nullptr; int error = avformat_open_input(&formatContext, video_path.c_str(), nullptr, nullptr); checkError(error, "Error opening input file"); //Read packets of a media file to get stream information. error = avformat_find_stream_info(formatContext, nullptr); checkError(error, "Error avformat find stream info"); // find the video stream AVStream* videoStream = nullptr; for (unsigned int i = 0; i < formatContext->nb_streams; i++) { if (formatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO && !videoStream) { videoStream = formatContext->streams[i]; } } if (!videoStream) { std::cerr codec_id); AVCodecContext* videoCodecContext = avcodec_alloc_context3(videoCodec); if (!videoCodecContext) { std::cerr

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