FFMPEG+Qt 实时显示本机USB摄像头1080p画面以及同步录制mp4视频

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1、前言

  本文通过FFMPEG(7.0.2)与Qt(5.13.2)实现在windows10系统下，实时预览以及录制1080p视频。
  本文程序只对视频数据进行处理，不考虑音频数据。

1.1 目标

  在win10平台，用FFMPEG和Qt实现实时显示USB摄像头画面以及同步录制mp4视频。

1.2 一些说明

  本程序实现USB摄像头数据视频流获取及显示，录制、显示的视频质量与USB相机有关，本人摄像头为1920*1080@30Hz。
  USB相机默认视频流格式会有差别，如果需要特定格式及分辨率的时候，需要手动设置。
  大部分USB摄像头有MJPG和YUV两种格式，为了追求高分辨率，可以将摄像头参数设置为MJPG输入。需要通过以下代码实现。即配置AVDictionary。需要同时配置相机的帧率、分辨率和格式，不能只设置输入格式！要不然不成功。

AVDictionary* options = NULL;
av_dict_set(&options, "input_format", "mjpeg", 0);
av_dict_set(&options, "framerate", "30", 0);
av_dict_set(&options, "video_size", "1920x1080", 0);avformat_open_input(&pFormatCtx_, in_file.c_str(), ifmt, &options);

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2、效果

  先看演示效果视频：

3、代码

  本项目全部代码请到此处获取：https://download.csdn.net/download/wang_chao118/89921908

3.1 思路

  通过Qt进行画面可视化，FFMPEG对USB视频流进行解码、编码以及存储。将FFMPEG的循环操作放到一个子线程中，与现实线程隔离。
  通过Qt的信号槽机制，将FFMPEG循环操作过程中解码出的单帧图像转化成QImage*通过信号传递至主线程进行图像绘制。

thread_ = new std::thread(&CameraThread::Run, this);

QObject::connect(camera_thread_, &CameraThread::frameReady, &w, &Widget::updatePic);

3.2 工程目录

  本项目中将FFMPEG相关上下文的初始化、解码、编码、记录循环功能集成在一个CameraThread类中。
  CameraThread类继承Thread类。Thread类中实现子线程的初始化、开始、停止、运行等基础功能。

3.3 核心代码

  CameraThread::Start()函数用于初始化FFMPEG的各类上下文，设置解码器、编码器参数等，在Qt界面中只要点击“开始录制”按钮就会调用该函数，点击“停止录制”按钮调用CameraThread::Stop()函数，对上下文进行清理。

int CameraThread::Start()
{start_pts = 0;int ret = 0;/******************************************打开摄像头设备********************************************/const AVInputFormat* m_inputFormat = av_find_input_format("dshow");inputContext = avformat_alloc_context();AVDictionary *options = nullptr;ret = avformat_open_input(&inputContext, url_.c_str(), m_inputFormat, &options);if (ret < 0){qDebug()<<"avformat_open_input failed, ret: "<<ret;return -1;}// 获取摄像头流信息ret = avformat_find_stream_info(inputContext, nullptr);if (ret < 0){qDebug()<<"Could not retrieve input stream information";return -1;}int videoStreamId = -1;videoStreamId = av_find_best_stream(inputContext, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, NULL);inputStream = inputContext->streams[videoStreamId];codecParameters = inputStream->codecpar;// 获取摄像头的实际分辨率和帧率int actual_width = codecParameters->width;int actual_height = codecParameters->height;AVRational actual_frame_rate = inputStream->r_frame_rate;qDebug()<< "Camera Resolution: " << actual_width << "x" << actual_height;qDebug()<< "Camera Frame Rate: " << actual_frame_rate.num << "/" << actual_frame_rate.den << " fps";/******************************************创建解码器********************************************/// 查找解码器auto codec_id = inputStream->codecpar->codec_id;const AVCodec* decoder = avcodec_find_decoder(codec_id);if (!decoder) {qDebug()<<"Unsupported codec !";return -1;}// 创建解码器上下文decoderContext = avcodec_alloc_context3(decoder);ret = avcodec_parameters_to_context(decoderContext, codecParameters);if (ret<0) {qDebug()<<"Failed to copy codec parameters to decoder context.";return -1;}qDebug() << " output pix_fmt=" << av_get_pix_fmt_name((AVPixelFormat)codecParameters->format) <<" "<< codecParameters->format;ret = avcodec_open2(decoderContext, decoder, nullptr);if (ret<0) {qDebug()<<"Failed to open decoder.";return -1;}/******************************************创建编码器********************************************/// 查找 H.264 编码器const AVCodec* pEncoderH264 = avcodec_find_encoder(AV_CODEC_ID_H264);if (pEncoderH264 == NULL) {qDebug() << "Unsupported encodec.";return -1;}//视频编码器上下文encoderContext = avcodec_alloc_context3(pEncoderH264);encoderContext->time_base.num = inputStream->time_base.num;encoderContext->time_base.den = inputStream->time_base.den;encoderContext->has_b_frames = 0;
//    encoderContext->gop_size = 50;encoderContext->codec_id = pEncoderH264->id;encoderContext->pix_fmt = (AVPixelFormat)inputStream->codecpar->format;qDebug()<<"111111111111111111111111111111: "<<encoderContext->pix_fmt;encoderContext->width = inputStream->codecpar->width;encoderContext->height = inputStream->codecpar->height;
//    encoderContext->bit_rate = 0;encoderContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;encoderContext->framerate = inputStream->avg_frame_rate;//编码帧率按照采集帧率来
//    encoderContext->bit_rate = 5000000;               //数值越小文件越小//编码器不用等待缓冲区填满，接收到数据即开始编码av_opt_set(encoderContext->priv_data, "tune", "zerolatency", 0);
//    av_opt_set(encoderContext->priv_data, "crf", "23", 0);               //数值越大越模糊，存储文件越小qDebug() << "encoder h246 information:";qDebug() << " encode fps=" << (encoderContext->framerate.num / encoderContext->framerate.den) ;qDebug() << " w=" << encoderContext->width << ", h=" << encoderContext->height;qDebug() << " input pix format=" << av_get_pix_fmt_name(encoderContext->pix_fmt) <<" "<< encoderContext->pix_fmt ;ret = avcodec_open2(encoderContext, pEncoderH264, NULL);if (ret < 0) {qDebug() <<"avcodec_open2";return -1;}/******************************************创建视频输出文件********************************************/const AVOutputFormat* outputFormat = av_guess_format("mp4", NULL, NULL);outputContext = avformat_alloc_context();outputContext->oformat = const_cast<AVOutputFormat*>(outputFormat);// 创建输出流outputStream = avformat_new_stream(outputContext, encoderContext->codec);if (!outputStream){qDebug() <<"Failed to create output stream";return -1;}avcodec_parameters_from_context(outputStream->codecpar, encoderContext);outputStream->time_base = av_inv_q(inputStream->r_frame_rate);// 创建输出 MP4 文件mp4_count++;m_mp4_file_name = m_mp4_file_name_header + std::to_string(mp4_count) + ".mp4";ret = avio_open(&outputContext->pb, m_mp4_file_name.c_str(), AVIO_FLAG_WRITE);if(ret <0){qDebug() <<"Failed to create output file.";return -1;}ret = avformat_write_header(outputContext, NULL);if(ret <0){qDebug() <<"Failed to write header";return -1;}/******************************************开线程****************************************************/thread_ = new std::thread(&CameraThread::Run, this);if (!thread_){qDebug()<<"new std::thread(&CameraThread::Run, this) failed";return -1;}return 0;
}

  CameraThread::Run()函数是循环录制过程的执行函数，主要是从FFMPEG上下文中取出视频数据包AVPacket，解码至视频帧AVFrame，再按相应格式（H264）编码成AVPacket，然后再保存至文件中。

void CameraThread::Run()
{qDebug() << "Run into CameraThread::Run()!";int ret = 0;SwsContext *sws_ctx = nullptr;while (!abort_){// 读取视频帧ret = av_read_frame(inputContext, captured_packet);if (ret < 0){qDebug() << "av_read_frame error";continue; // 如果读取失败，跳过到下一帧}// start capture pts from 0// 初始化 start_ptsif (start_pts == 0){start_pts = captured_packet->pts; // 仅在第一次读取时设置}captured_packet->pts -= start_pts;qDebug()<<"captured_packet->pts: "<<captured_packet->pts;av_log(nullptr, AV_LOG_INFO, "packet size is %d\n", captured_packet->size);// 解码 MJPEG 数据ret = avcodec_send_packet(decoderContext, captured_packet);if (ret < 0){qDebug() << "Error sending packet for decoding.";av_packet_unref(captured_packet); // 释放 packet 内存continue; // 继续读取下一个包}auto decoded_frame = av_frame_alloc();ret = avcodec_receive_frame(decoderContext, decoded_frame); // decoded_frame 自带引用计数if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF){av_frame_free(&decoded_frame); // 确保在这些情况下也释放内存av_packet_unref(captured_packet); // 释放 packet 内存continue;}else if (ret < 0){qDebug() << "avcodec_receive_frame failed!";av_frame_free(&decoded_frame);av_packet_unref(captured_packet); // 释放 packet 内存break;}// 编码 H264 数据ret = avcodec_send_frame(encoderContext, decoded_frame);if (ret < 0){qDebug() << "Error sending frame for encoding.";av_frame_free(&decoded_frame);av_packet_unref(captured_packet); // 释放 packet 内存continue;}/******************************************发送QImage***********************************************/// 转换解码后的帧为 QImageif (!sws_ctx){sws_ctx = sws_getContext(decoded_frame->width, decoded_frame->height,(AVPixelFormat)decoded_frame->format,decoded_frame->width, decoded_frame->height,AV_PIX_FMT_RGB32, SWS_BILINEAR, nullptr, nullptr, nullptr);}QImage image(decoded_frame->width, decoded_frame->height, QImage::Format_RGB32);uint8_t *dst[4] = { image.bits(), nullptr, nullptr, nullptr };int dstStride[4] = { image.bytesPerLine(), 0, 0, 0 };sws_scale(sws_ctx, decoded_frame->data, decoded_frame->linesize, 0,decoded_frame->height, dst, dstStride);// 发射信号emit frameReady(image);/******************************************存视频****************************************************/ret = avcodec_receive_packet(encoderContext, h264_pkt);if (ret < 0){qDebug() << "avcodec_receive_packet error.";av_frame_free(&decoded_frame);av_packet_unref(captured_packet); // 释放 packet 内存continue;}ret = av_write_frame(outputContext, h264_pkt);if (ret < 0){qDebug() << "write error.";}// 释放 decoded_frame 和 packet 内存av_frame_free(&decoded_frame);av_packet_unref(captured_packet); // 释放 packet 内存}
}

4、全部代码获取

  本项目全部代码请到此处获取：https://download.csdn.net/download/wang_chao118/89921908