1st, Motivation and First Steps

// Copyright 2020 Lisandro Bravo.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <memory>
#include <string>
#include <vector>

#include "absl/strings/str_split.h"
#include "mediapipe/calculators/video/opencv_video_encoder_calculator.pb.h"
#include "mediapipe/framework/calculator_framework.h"
#include "mediapipe/framework/formats/image_frame.h"
#include "mediapipe/framework/formats/image_frame_opencv.h"
#include "mediapipe/framework/formats/video_stream_header.h"
#include "mediapipe/framework/port/file_helpers.h"
#include "mediapipe/framework/port/opencv_highgui_inc.h"
#include "mediapipe/framework/port/opencv_imgproc_inc.h"
#include "mediapipe/framework/port/opencv_video_inc.h"
#include "mediapipe/framework/port/ret_check.h"
#include "mediapipe/framework/port/source_location.h"
#include "mediapipe/framework/port/status.h"
#include "mediapipe/framework/port/status_builder.h"
#include "mediapipe/framework/tool/status_util.h"

namespace mediapipe {

// Encodes the input video stream and produces a media file.
// The media file can be output to the output_file_path specified as a side
// packet. Currently, the calculator only supports one video stream (in
// mediapipe::ImageFrame).
//
// Example config to generate the output video file:
//
// node {
//   calculator: "OpenCvVideoImShowCalculator"
//   input_stream: "VIDEO:video"
//   input_stream: "VIDEO_PRESTREAM:video_header"
//   input_side_packet: "OUTPUT_FILE_PATH:output_file_path"
//   node_options {
//     [type.googleapis.com/mediapipe.OpenCvVideoImShowCalculatorOptions]: {
//        codec: "avc1"
//        video_format: "mp4"
//     }
//   }
// }
class OpenCvVideoImShowCalculator : public CalculatorBase {
 public:
  static ::mediapipe::Status GetContract(CalculatorContract* cc);
  ::mediapipe::Status Open(CalculatorContext* cc) override;
  ::mediapipe::Status Process(CalculatorContext* cc) override;
  ::mediapipe::Status Close(CalculatorContext* cc) override;

 private:
  ::mediapipe::Status SetUpVideoWriter();

  std::string output_file_path_;
  int four_cc_;

  std::unique_ptr<cv::VideoWriter> writer_;
};

::mediapipe::Status OpenCvVideoImShowCalculator::GetContract(
    CalculatorContract* cc) {
  RET_CHECK(cc->Inputs().HasTag("VIDEO"));
  cc->Inputs().Tag("VIDEO").Set<ImageFrame>();
  if (cc->Inputs().HasTag("VIDEO_PRESTREAM")) {
    cc->Inputs().Tag("VIDEO_PRESTREAM").Set<VideoHeader>();
  }
  //RET_CHECK(cc->InputSidePackets().HasTag("OUTPUT_FILE_PATH"));
  //cc->InputSidePackets().Tag("OUTPUT_FILE_PATH").Set<std::string>();
  return ::mediapipe::OkStatus();
}

::mediapipe::Status OpenCvVideoImShowCalculator::Open(CalculatorContext* cc) {
  OpenCvVideoEncoderCalculatorOptions options =
      cc->Options<OpenCvVideoEncoderCalculatorOptions>();
  RET_CHECK(options.has_codec() && options.codec().length() == 4)
      << "A 4-character codec code must be specified in "
         "OpenCvVideoEncoderCalculatorOptions";
  const char* codec_array = options.codec().c_str();
  four_cc_ = mediapipe::fourcc(codec_array[0], codec_array[1], codec_array[2],
                               codec_array[3]);
  RET_CHECK(!options.video_format().empty())
      << "Video format must be specified in "
         "OpenCvVideoEncoderCalculatorOptions";
 /* output_file_path_ =
      cc->InputSidePackets().Tag("OUTPUT_FILE_PATH").Get<std::string>();
  std::vector<std::string> splited_file_path =
      absl::StrSplit(output_file_path_, '.');
  RET_CHECK(splited_file_path.size() >= 2 &&
            splited_file_path[splited_file_path.size() - 1] ==
                options.video_format())
      << "The output file path is invalid.";*/
  // If the video header will be available, the video metadata will be fetched
  // from the video header directly. The calculator will receive the video
  // header packet at timestamp prestream.
  if (cc->Inputs().HasTag("VIDEO_PRESTREAM")) {
    return ::mediapipe::OkStatus();
  }
  return SetUpVideoWriter();
}

::mediapipe::Status OpenCvVideoImShowCalculator::Process(
    CalculatorContext* cc) {
  if (cc->InputTimestamp() == Timestamp::PreStream()) {
    //const VideoHeader& video_header =
    //    cc->Inputs().Tag("VIDEO_PRESTREAM").Get<VideoHeader>();
    return SetUpVideoWriter();
  }

  const ImageFrame& image_frame =
      cc->Inputs().Tag("VIDEO").Value().Get<ImageFrame>();
  ImageFormat::Format format = image_frame.Format();
  cv::Mat frame;
  if (format == ImageFormat::GRAY8) {
    frame = formats::MatView(&image_frame);
    if (frame.empty()) {
      return ::mediapipe::InvalidArgumentErrorBuilder(MEDIAPIPE_LOC)
             << "Receive empty frame at timestamp "
             << cc->Inputs().Tag("VIDEO").Value().Timestamp()
             << " in OpenCvVideoImShowCalculator::Process()";
    }
  } else {
    cv::Mat tmp_frame = formats::MatView(&image_frame);
    if (tmp_frame.empty()) {
      return ::mediapipe::InvalidArgumentErrorBuilder(MEDIAPIPE_LOC)
             << "Receive empty frame at timestamp "
             << cc->Inputs().Tag("VIDEO").Value().Timestamp()
             << " in OpenCvVideoImShowCalculator::Process()";
    }
    if (format == ImageFormat::SRGB) {
      cv::cvtColor(tmp_frame, frame, cv::COLOR_RGB2BGR);
    } else if (format == ImageFormat::SRGBA) {
      cv::cvtColor(tmp_frame, frame, cv::COLOR_RGBA2BGR);
    } else {
      return ::mediapipe::InvalidArgumentErrorBuilder(MEDIAPIPE_LOC)
             << "Unsupported image format: " << format;
    }
  }
  cv::imshow("MediaPipe",frame);
  cv::waitKey(25);
  
  return ::mediapipe::OkStatus();
}

::mediapipe::Status OpenCvVideoImShowCalculator::Close(CalculatorContext* cc) {
  //cv::destroyAllWindows();
  return ::mediapipe::OkStatus();
}

::mediapipe::Status OpenCvVideoImShowCalculator::SetUpVideoWriter() {

  cv::namedWindow("MediaPipe",cv::WINDOW_GUI_EXPANDED);
  return ::mediapipe::OkStatus();
}

REGISTER_CALCULATOR(OpenCvVideoImShowCalculator);
}  // namespace mediapipe