From 758c1ba16ab87152621f6c7c62c2e011a2ae2712 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Tue, 11 Jan 2022 16:42:30 +0100
Subject: [PATCH] Fix failure to decode multiple video frames from one packet
 (#2159).

---
 src/lib/ffmpeg_decoder.cc         | 24 ++++++++++++------------
 test/ffmpeg_decoder_error_test.cc | 11 +++++++++++
 test/player_test.cc               |  2 +-
 3 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index f64ccbd3b..b2a1bbbe0 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -538,17 +538,19 @@ FFmpegDecoder::decode_and_process_video_packet (AVPacket* packet)
 		LOG_WARNING("avcodec_send_packet returned %1 for a video packet", r);
 	}
 
-	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);
-	}
+	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 ();
+		process_video_frame ();
+	}
 
 	return true;
 }
@@ -557,8 +559,6 @@ FFmpegDecoder::decode_and_process_video_packet (AVPacket* packet)
 void
 FFmpegDecoder::process_video_frame ()
 {
-	/* We assume we'll only get one frame here, which I think is safe */
-
 	boost::mutex::scoped_lock lm (_filter_graphs_mutex);
 
 	shared_ptr<VideoFilterGraph> graph;
diff --git a/test/ffmpeg_decoder_error_test.cc b/test/ffmpeg_decoder_error_test.cc
index 368f54e3c..414c61384 100644
--- a/test/ffmpeg_decoder_error_test.cc
+++ b/test/ffmpeg_decoder_error_test.cc
@@ -22,6 +22,7 @@
 #include "lib/content.h"
 #include "lib/content_factory.h"
 #include "lib/dcpomatic_time.h"
+#include "lib/player.h"
 #include "test.h"
 #include <boost/test/unit_test.hpp>
 
@@ -46,3 +47,13 @@ BOOST_AUTO_TEST_CASE (check_exception_during_flush)
 }
 
 
+
+BOOST_AUTO_TEST_CASE (check_exception_with_multiple_video_frames_per_packet)
+{
+	auto content = content_factory(TestPaths::private_data() / "chk.mkv").front();
+	auto film = new_test_film2 ("check_exception_with_multiple_video_frames_per_packet", { content });
+	auto player = std::make_shared<Player>(film, film->playlist());
+
+	while (!player->pass()) {}
+}
+
diff --git a/test/player_test.cc b/test/player_test.cc
index cafb14586..0d3af5f8c 100644
--- a/test/player_test.cc
+++ b/test/player_test.cc
@@ -210,7 +210,7 @@ BOOST_AUTO_TEST_CASE (player_interleave_test)
 	player->Audio.connect (bind (&audio, _1, _2));
 	video_frames = audio_frames = 0;
 	while (!player->pass ()) {
-		BOOST_CHECK (abs(video_frames - (audio_frames / 2000)) < 8);
+		BOOST_CHECK (abs(video_frames - (audio_frames / 2000)) <= 8);
 	}
 }
 
-- 
2.30.2