From 141e8bdd4ce1542cb927ed88e05bae6dd4d9acfc Mon Sep 17 00:00:00 2001
From: Selim Mustafaev <selim@fastmail.fm>
Date: Sat, 27 Aug 2016 22:59:42 +0300
Subject: [PATCH] Video transcoding kind of works (at least if input video
 frames has correct pts/dts)

---
 main.cpp | 77 +++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 48 insertions(+), 29 deletions(-)

diff --git a/main.cpp b/main.cpp
index 8bc1195..0830a8e 100644
--- a/main.cpp
+++ b/main.cpp
@@ -8,7 +8,7 @@ void checkResult(int res, const char* msg) {
 	if(res < 0) {
 		char errStr[260];
 		av_strerror(res, errStr, 260);
-		std::cout << msg << ": " << errStr << std::endl;
+		std::cerr << msg << ": " << errStr << std::endl;
 	}
 }
 
@@ -49,21 +49,6 @@ int main(int argc, char** argv) {
 	AVCodec* dstVCodec = avcodec_find_encoder(AV_CODEC_ID_H264);
 	if(!dstVCodec) std::cout << "cannot find encoder" << std::endl;
 
-	AVCodecContext* dstVCodecCtx = avcodec_alloc_context3(dstVCodec);
-	if(!dstVCodecCtx) std::cout << "cannot allocate context" << std::endl;
-
-	dstVCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;
-	dstVCodecCtx->width = codecCtx->width;
-	dstVCodecCtx->height = codecCtx->height;
-	dstVCodecCtx->time_base = codecCtx->time_base;
-    outFmtCtx->duration = inFmtCtx->duration;
-
-	res = avcodec_open2(dstVCodecCtx, dstVCodec, nullptr);
-	checkResult(res, "cannot open codec for encoding");
-
-	if(outFmtCtx->oformat->flags & AVFMT_GLOBALHEADER)
-		dstVCodecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;
-
 	AVStream* outVideoStream = avformat_new_stream(outFmtCtx, dstVCodec);
 	if(!outVideoStream) std::cout << "cannot create output video stream" << std::endl;
 
@@ -74,15 +59,29 @@ int main(int argc, char** argv) {
 
 	av_dump_format(outFmtCtx, 0, argv[2], 1);
 
+	AVCodecContext* dstVCodecCtx = outVideoStream->codec;
+	dstVCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;
+	dstVCodecCtx->width = codecCtx->width;
+	dstVCodecCtx->height = codecCtx->height;
+	//dstVCodecCtx->time_base = codecCtx->time_base;
+	outVideoStream->time_base = codecCtx->time_base;
+	outFmtCtx->duration = inFmtCtx->duration;
+
+	if(outFmtCtx->oformat->flags & AVFMT_GLOBALHEADER)
+		dstVCodecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;
+
+	res = avcodec_open2(dstVCodecCtx, dstVCodec, nullptr);
+	checkResult(res, "cannot open codec for encoding");
+
 	res = avformat_write_header(outFmtCtx, nullptr);
 	checkResult(res, "error writing header to output file");
 
-	AVPacket packet;
-	packet.data = nullptr;
-	packet.size = 0;
 	AVFrame* frame = nullptr;
     int gotPicture = 0, gotPacket = 0, decodedFrames = 1;
 	while(true) {
+		AVPacket packet;
+		packet.data = nullptr;
+		packet.size = 0;
 		res = av_read_frame(inFmtCtx, &packet);
 		if(res < 0) break;
 
@@ -99,7 +98,8 @@ int main(int argc, char** argv) {
 
 			if(gotPicture) {
 				frame->pts = av_frame_get_best_effort_timestamp(frame);
-				std::cout << "decoded frame: " << decodedFrames++ << std::endl;
+                frame->pict_type = AV_PICTURE_TYPE_NONE;
+                //std::cout << "decoded frame: " << decodedFrames++ << " pts: " << frame->pts << ", dts: " << frame->pkt_dts << std::endl;
 
 				AVPacket encPacket;
 				encPacket.data = nullptr;
@@ -107,19 +107,12 @@ int main(int argc, char** argv) {
 				av_init_packet(&encPacket);
 				encPacket.stream_index = 0;
 
-				encPacket.pts = decodedFrames;
-				encPacket.dts = decodedFrames;
-
 				res = avcodec_encode_video2(dstVCodecCtx, &encPacket, frame, &gotPacket);
 				av_frame_free(&frame);
 				if(res < 0) break;
 				if(!gotPacket) continue;
 
-				AVStream *st = outFmtCtx->streams[encPacket.stream_index];
-				auto x = st->codec->has_b_frames;
-				auto y = st->codec->max_b_frames;
-
-				//av_packet_rescale_ts(&encPacket, st->codec->time_base, st->time_base);
+				av_packet_rescale_ts(&encPacket, videoStream->time_base, outVideoStream->time_base);
 
 				res = av_interleaved_write_frame(outFmtCtx, &encPacket);
 				checkResult(res, "cannot write frame to output file");
@@ -130,8 +123,34 @@ int main(int argc, char** argv) {
 		av_free_packet(&packet);
 	}
 
-	av_write_trailer(outFmtCtx);
+    // flush encoder
+    if(dstVCodecCtx->codec->capabilities & AV_CODEC_CAP_DELAY) {
+        std::cout << "flushing encoder" << std::endl;
+        int gotFrame = 0;
+        while (1) {
+            AVPacket encPacket;
+            encPacket.data = nullptr;
+            encPacket.size = 0;
+            av_init_packet(&encPacket);
+            encPacket.stream_index = 0;
+            res = avcodec_encode_video2(dstVCodecCtx, &encPacket, nullptr, &gotFrame);
+            if (res < 0) {
+	            std::cout << "avcodec_encode_video2 failed" << std::endl;
+	            break;
+            }
+            if (gotFrame) {
+                //std::cout << "extra frame" << std::endl;
+	            av_packet_rescale_ts(&encPacket, videoStream->time_base, outVideoStream->time_base);
+                res = av_interleaved_write_frame(outFmtCtx, &encPacket);
+	            checkResult(res, "[flush encoder] cannot write frame to output file");
+            } else {
+	            break;
+            }
+        }
+    }
 
+    res = av_write_trailer(outFmtCtx);
+    checkResult(res, "error writing trailer to output file");
 
 	if(codecCtx)
 		avcodec_close(codecCtx);