From 80430058f5eefb55147218a85225adeb6b616f4d Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Tue, 15 Feb 2022 22:47:48 +0100
Subject: [PATCH] Try to handle EAGAIN from avcodec_send_packet() properly.

The docs say on EAGAIN we should call avcodec_receive_frame()
and then re-send the same packet again.  This should do that.

This is a fix for errors trigged by the accompanying test.
---
 src/lib/ffmpeg_decoder.cc    | 38 +++++++++++++++++++++---------------
 src/lib/ffmpeg_examiner.cc   | 33 +++++++++++++++++--------------
 test/ffmpeg_examiner_test.cc |  7 +++++++
 3 files changed, 47 insertions(+), 31 deletions(-)

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index b2a1bbbe0..d49878217 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -533,24 +533,30 @@ FFmpegDecoder::decode_and_process_video_packet (AVPacket* packet)
 
 	auto context = video_codec_context();
 
-	int r = avcodec_send_packet (context, packet);
-	if (r < 0) {
-		LOG_WARNING("avcodec_send_packet returned %1 for a video packet", r);
-	}
-
-	while (true) {
-		r = avcodec_receive_frame (context, _video_frame);
-		if (r == AVERROR(EAGAIN) || r == AVERROR_EOF || (r < 0 && !packet)) {
-			/* More input is required, no more frames are coming, or we are flushing and there was
-			 * some error which we just want to ignore.
-			 */
-			return false;
-		} else if (r < 0) {
-			throw DecodeError (N_("avcodec_receive_frame"), N_("FFmpeg::decode_and_process_video_packet"), r);
+	bool pending = false;
+	do {
+		int r = avcodec_send_packet (context, packet);
+		if (r < 0) {
+			LOG_WARNING("avcodec_send_packet returned %1 for a video packet", r);
 		}
 
-		process_video_frame ();
-	}
+		/* EAGAIN means we should call avcodec_receive_frame and then re-send the same packet */
+		pending = r == AVERROR(EAGAIN);
+
+		while (true) {
+			r = avcodec_receive_frame (context, _video_frame);
+			if (r == AVERROR(EAGAIN) || r == AVERROR_EOF || (r < 0 && !packet)) {
+				/* More input is required, no more frames are coming, or we are flushing and there was
+				 * some error which we just want to ignore.
+				 */
+				return false;
+			} else if (r < 0) {
+				throw DecodeError (N_("avcodec_receive_frame"), N_("FFmpeg::decode_and_process_video_packet"), r);
+			}
+
+			process_video_frame ();
+		}
+	} while (pending);
 
 	return true;
 }
diff --git a/src/lib/ffmpeg_examiner.cc b/src/lib/ffmpeg_examiner.cc
index 3c6d185f4..fab999006 100644
--- a/src/lib/ffmpeg_examiner.cc
+++ b/src/lib/ffmpeg_examiner.cc
@@ -221,22 +221,25 @@ FFmpegExaminer::video_packet (AVCodecContext* context, string& temporal_referenc
 		return false;
 	}
 
-	int r = avcodec_send_packet (context, packet);
-	if (r < 0 && !(r == AVERROR_EOF && !packet)) {
-		/* We could cope with AVERROR(EAGAIN) and re-send the packet but I think it should never happen.
-		 * AVERROR_EOF can happen during flush if we've already sent a flush packet.
-		 */
-		throw DecodeError (N_("avcodec_send_packet"), N_("FFmpegExaminer::video_packet"), r);
-	}
+	bool pending = false;
+	do {
+		int r = avcodec_send_packet (context, packet);
+		if (r < 0) {
+			LOG_WARNING("avcodec_send_packet returned %1 for a video packet", r);
+		}
 
-	r = avcodec_receive_frame (context, _video_frame);
-	if (r == AVERROR(EAGAIN)) {
-		/* More input is required */
-		return true;
-	} else if (r == AVERROR_EOF) {
-		/* No more output is coming */
-		return false;
-	}
+		/* EAGAIN means we should call avcodec_receive_frame and then re-send the same packet */
+		pending = r == AVERROR(EAGAIN);
+
+		r = avcodec_receive_frame (context, _video_frame);
+		if (r == AVERROR(EAGAIN)) {
+			/* More input is required */
+			return true;
+		} else if (r == AVERROR_EOF) {
+			/* No more output is coming */
+			return false;
+		}
+	} while (pending);
 
 	if (!_first_video) {
 		_first_video = frame_time (_video_frame, _format_context->streams[_video_stream.get()]);
diff --git a/test/ffmpeg_examiner_test.cc b/test/ffmpeg_examiner_test.cc
index c460830fb..2c244f541 100644
--- a/test/ffmpeg_examiner_test.cc
+++ b/test/ffmpeg_examiner_test.cc
@@ -76,3 +76,10 @@ BOOST_AUTO_TEST_CASE (ffmpeg_examiner_vob_test)
 	auto examiner = make_shared<FFmpegExaminer>(content);
 }
 
+
+/** Check that another file can be examined without error */
+BOOST_AUTO_TEST_CASE (ffmpeg_examiner_mkv_test)
+{
+	auto content = make_shared<FFmpegContent>(TestPaths::private_data() / "sample.mkv");
+	auto examiner = make_shared<FFmpegExaminer>(content);
+}
-- 
2.30.2