Ignore errors from avcodec_receive_frame when flushing video (#2035).

The test fails if we don't do this; it doesn't really seem 100%
convincing but we are already doing this for audio.

3 files changed, 55 insertions, 2 deletions

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index db88562ea..c5c41fdac 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -548,9 +548,13 @@ FFmpegDecoder::decode_and_process_video_packet (AVPacket* packet)
 	}
 
 	r = avcodec_receive_frame (context, _frame);
-	if (r == AVERROR(EAGAIN) || r == AVERROR_EOF) {
-		/* More input is required, or no more frames are coming */
+	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);
 	}
 
 	/* We assume we'll only get one frame here, which I think is safe */
diff --git a/test/ffmpeg_decoder_error_test.cc b/test/ffmpeg_decoder_error_test.cc
new file mode 100644
index 000000000..b3e9e4293
--- /dev/null
+++ b/test/ffmpeg_decoder_error_test.cc
@@ -0,0 +1,48 @@
+/*
+    Copyright (C) 2021 Carl Hetherington <cth@carlh.net>
+
+    This file is part of DCP-o-matic.
+
+    DCP-o-matic is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    DCP-o-matic is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with DCP-o-matic.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+
+#include "lib/content.h"
+#include "lib/content_factory.h"
+#include "lib/dcpomatic_time.h"
+#include "test.h"
+#include <boost/test/unit_test.hpp>
+
+
+/** @defgroup regression Tests to make sure that old bugs do not reappear */
+
+/** @file  test/ffmpeg_decoder_erro_test.cc
+ *  @brief Check some bugs in the FFmpegDecoder
+ *  @ingroup regression
+ */
+
+
+BOOST_AUTO_TEST_CASE (check_exception_during_flush)
+{
+	auto content = content_factory(TestPaths::private_data() / "3d_thx_broadway_2010_lossless.m2ts").front();
+	auto film = new_test_film2 ("check_exception_during_flush", { content });
+
+	content->set_trim_start (dcpomatic::ContentTime(2310308));
+	content->set_trim_end (dcpomatic::ContentTime(116020));
+
+	make_and_verify_dcp (film);
+}
+
+
diff --git a/test/wscript b/test/wscript
index 6ef9ac752..5774ffebf 100644
--- a/test/wscript
+++ b/test/wscript
@@ -73,6 +73,7 @@ def build(bld):
                  ffmpeg_audio_only_test.cc
                  ffmpeg_audio_test.cc
                  ffmpeg_dcp_test.cc
+                 ffmpeg_decoder_error_test.cc
                  ffmpeg_decoder_seek_test.cc
                  ffmpeg_decoder_sequential_test.cc
                  ffmpeg_encoder_test.cc