added example of saving preview of video file in png picture

examples/CMakeLists.txt

@@ -1,5 +1,9 @@
 project(ffConv)
-
 add_executable(ffConv ffConv.cpp)
 add_dependencies(ffConv ffcpp)
 target_link_libraries(ffConv ffcpp)
+
+project(ffPreview)
+add_executable(ffPreview ffPreview.cpp)
+add_dependencies(ffPreview ffcpp)
+target_link_libraries(ffPreview ffcpp)

examples/ffPreview.cpp

@@ -0,0 +1,48 @@
+#include "ffcpp/ffcpp.h"
+#include "ffcpp/MediaFile.h"
+#include "ffcpp/Scaler.h"
+
+namespace ff = ffcpp;
+
+size_t KEY_FRAME_TO_SAVE = 0;
+
+int main(int argc, char** argv) {
+	ff::init();
+	ff::MediaFile input(argv[1], ff::Mode::Read);
+	ff::MediaFile output(argv[2], ff::Mode::Write);
+
+	ff::Stream& vStream = input.videoStream();
+	ff::Codec& vDecoder = vStream.codec();
+
+	ff::Stream& outVStream = output.addVideoStream(AV_CODEC_ID_PNG, vDecoder.width(), vDecoder.height(), vStream.timeBase(), AV_PIX_FMT_RGB24);
+	ff::Codec& vEncoder = outVStream.codec();
+
+	output.writeHeader();
+
+	size_t curKeyFrame = 0;
+	ff::Scaler scaler(vDecoder, vEncoder);
+	while(auto packet = input.readPacket()) {
+		AVMediaType packetType = input.packetType(packet);
+		if(packetType == AVMEDIA_TYPE_VIDEO) {
+			auto frame = vDecoder.decode(packet);
+			if(frame.isKeyFrame() && (frame.pts() > 0 || KEY_FRAME_TO_SAVE == 0)) {
+				if(curKeyFrame == KEY_FRAME_TO_SAVE) {
+					frame = scaler.scale(frame);
+					frame.setPictureType(AV_PICTURE_TYPE_NONE);
+					auto encPacket = vEncoder.encode(frame);
+					if(!encPacket) continue;
+					encPacket.setStreamIndex(0);
+					encPacket.rescaleTimestamps(vStream.timeBase(), outVStream.timeBase());
+					output.writePacket(encPacket);
+					break;
+				} else {
+					++curKeyFrame;
+				}
+			}
+		}
+	}
+
+	output.writeTrailer();
+
+	return 0;
+}

include/ffcpp/Frame.h

@@ -28,6 +28,8 @@ namespace ffcpp {
 		void setPictureType(AVPictureType type);
 		int samplesCount() const;
 		void setPts(int pts);
+		bool isKeyFrame() const;
+		int pts() const;
 	};
 
 }

src/Frame.cpp

@@ -74,4 +74,12 @@ namespace ffcpp {
 		_frame->pts = pts;
 	}
 
+	bool Frame::isKeyFrame() const {
+		return (_frame->key_frame == 1);
+	}
+
+	int Frame::pts() const {
+		return _frame->pts;
+	}
+
 }