generate thumbnial with opencv nicely

CMakeLists.txt

@@ -12,6 +12,10 @@ pkg_check_modules(LIBAV REQUIRED IMPORTED_TARGET
    libswscale
    libavutil
 )
+# open cv
+pkg_check_modules(OPENCV REQUIRED IMPORTED_TARGET
+   opencv4
+)
 
 # compile_commands.json
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
@@ -26,4 +30,5 @@ add_executable(ThumbnailGenerator ${source_files})
 file (GLOB header_files "${source_dir}/*.hpp")
 target_include_directories(ThumbnailGenerator PUBLIC ${source_dir})
 
+target_link_libraries(ThumbnailGenerator PkgConfig::OPENCV)
 target_link_libraries(ThumbnailGenerator PkgConfig::LIBAV)

compile_commands.json

@@ -1,12 +1,12 @@
 [
 {
   "directory": "/home/talksik/code/cpp_thumbnail_generator/build",
-  "command": "/usr/bin/c++  -I/home/talksik/code/cpp_thumbnail_generator/./src -g -o CMakeFiles/ThumbnailGenerator.dir/src/Main.cpp.o -c /home/talksik/code/cpp_thumbnail_generator/src/Main.cpp",
+  "command": "/usr/bin/c++  -I/home/talksik/code/cpp_thumbnail_generator/./src -isystem /usr/include/opencv4 -g -o CMakeFiles/ThumbnailGenerator.dir/src/Main.cpp.o -c /home/talksik/code/cpp_thumbnail_generator/src/Main.cpp",
   "file": "/home/talksik/code/cpp_thumbnail_generator/src/Main.cpp"
 },
 {
   "directory": "/home/talksik/code/cpp_thumbnail_generator/build",
-  "command": "/usr/bin/c++  -I/home/talksik/code/cpp_thumbnail_generator/./src -g -o CMakeFiles/ThumbnailGenerator.dir/src/ThumbnailGenerator.cpp.o -c /home/talksik/code/cpp_thumbnail_generator/src/ThumbnailGenerator.cpp",
+  "command": "/usr/bin/c++  -I/home/talksik/code/cpp_thumbnail_generator/./src -isystem /usr/include/opencv4 -g -o CMakeFiles/ThumbnailGenerator.dir/src/ThumbnailGenerator.cpp.o -c /home/talksik/code/cpp_thumbnail_generator/src/ThumbnailGenerator.cpp",
   "file": "/home/talksik/code/cpp_thumbnail_generator/src/ThumbnailGenerator.cpp"
 }
 ]

src/ThumbnailGenerator.cpp

@@ -1,7 +1,10 @@
 #include "include/ThumbnailGenerator.hpp"
+#include <bits/types/FILE.h>
 #include <iostream>
 #include <libavutil/pixdesc.h>
 #include <libavutil/pixfmt.h>
+#include <opencv4/opencv2/opencv.hpp>
+
 extern "C" {
 #include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
@@ -37,7 +40,8 @@ int ThumbnailGenerator::get_duration_microseconds(std::string input_file_path) {
   return duration;
 }
 
-std::string ThumbnailGenerator::generate_thumbnail(std::string input_file_path) {
+std::string ThumbnailGenerator::generate_thumbnail(std::string input_file_path,
+                                                   int frame_number) {
   std::cout << "generating thumbnail: " << input_file_path << std::endl;
 
   // Open input file and allocate format context
@@ -95,6 +99,7 @@ std::string ThumbnailGenerator::generate_thumbnail(std::string input_file_path)
 
   // Read frames from the video stream
   while (av_read_frame(format_ctx, &packet) >= 0) {
+
     if (packet.stream_index == video_stream_idx) {
       // Decode video frame
       int ret = avcodec_send_packet(codec_ctx, &packet);
@@ -106,6 +111,14 @@ std::string ThumbnailGenerator::generate_thumbnail(std::string input_file_path)
       while (ret >= 0) {
         ret = avcodec_receive_frame(codec_ctx, frame);
 
+        if (codec_ctx->frame_number != frame_number) {
+          std::cout << "skipping frame: " << codec_ctx->frame_number
+                    << std::endl;
+          break;
+        } else {
+          std::cout << "found frame: " << codec_ctx->frame_number << std::endl;
+        }
+
         if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
           break;
         } else if (ret < 0) {
@@ -113,17 +126,42 @@ std::string ThumbnailGenerator::generate_thumbnail(std::string input_file_path)
           break;
         }
 
-        std::cout << "return value: " << ret << std::endl;
         std::cout << "frame->format: " << frame->format << std::endl;
         std::cout << frame->width << "x" << frame->height << std::endl;
         std::cout << frame->linesize[0] << std::endl;
 
+        // cv::Mat convertedMat(frame->height, frame->width, CV_8UC3,
+        //                      frame->data[0], frame->linesize[0]);
+        //
+        // std::cout << "convertedMat: " << convertedMat.cols << "x"
+        //           << convertedMat.rows << std::endl;
+
+        int width = frame->width;
+        int height = frame->height;
+        cv::Mat image(height, width, CV_8UC3);
+        int cvLinesizes[1];
+        cvLinesizes[0] = image.step1();
+        SwsContext *conversion =
+            sws_getContext(width, height, (AVPixelFormat)frame->format, width,
+                           height, AVPixelFormat::AV_PIX_FMT_BGR24,
+                           SWS_FAST_BILINEAR, NULL, NULL, NULL);
+        sws_scale(conversion, frame->data, frame->linesize, 0, height,
+                  &image.data, cvLinesizes);
+        sws_freeContext(conversion);
+
+        cv::imshow("Frame", image);
+        cv::waitKey(25);
+
+        cv::imwrite("output.jpg", image);
+
         // Print basic frame properties
         std::cout << "Frame " << codec_ctx->frame_number
                   << " (type=" << av_get_picture_type_char(frame->pict_type)
                   << ", size=" << frame->pkt_size << " bytes) pts "
                   << frame->pts << " key_frame " << frame->key_frame
                   << std::endl;
+
+        return "generateThumbnail: " + input_file_path;
       }
     }
 

src/include/ThumbnailGenerator.hpp

@@ -5,11 +5,12 @@ class ThumbnailGenerator {
 public:
   ThumbnailGenerator();
   // given a path to a video file, generate a thumbnail
-  std::string generate_thumbnail(std::string path);
+  std::string generate_thumbnail(std::string path, int frame_number = 1);
 
   // reads and simply prints out information about the video frames
   void read_video_frames(std::string path);
 
   int get_duration_microseconds(std::string path);
+
 private:
 };