From acfbd1c01020ea95d9e7eb3d63ddb14b9407732a Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Mon, 1 Feb 2021 01:24:55 +0100
Subject: [PATCH] Add noise to very small J2K frames (#1902).

---
 src/lib/dcp_video.cc     | 40 ++++++++++++++++++++++++++++------
 test/low_bitrate_test.cc | 47 ++++++++++++++++++++++++++++++++++++++++
 test/wscript             |  1 +
 3 files changed, 81 insertions(+), 7 deletions(-)
 create mode 100644 test/low_bitrate_test.cc

diff --git a/src/lib/dcp_video.cc b/src/lib/dcp_video.cc
index 58e10f0ed..cb1517727 100644
--- a/src/lib/dcp_video.cc
+++ b/src/lib/dcp_video.cc
@@ -124,15 +124,41 @@ DCPVideo::encode_locally ()
 {
 	auto const comment = Config::instance()->dcp_j2k_comment();
 
-	auto enc = dcp::compress_j2k (
-		convert_to_xyz (_frame, boost::bind(&Log::dcp_log, dcpomatic_log.get(), _1, _2)),
-		_j2k_bandwidth,
-		_frames_per_second,
-		_frame->eyes() == Eyes::LEFT || _frame->eyes() == Eyes::RIGHT,
-		_resolution == Resolution::FOUR_K,
-		comment.empty() ? "libdcp" : comment
+	ArrayData enc = {};
+	int constexpr minimum_size = 65536;
+
+	auto xyz = convert_to_xyz (_frame, boost::bind(&Log::dcp_log, dcpomatic_log.get(), _1, _2));
+	while (true) {
+		enc = dcp::compress_j2k (
+			xyz,
+			_j2k_bandwidth,
+			_frames_per_second,
+			_frame->eyes() == Eyes::LEFT || _frame->eyes() == Eyes::RIGHT,
+			_resolution == Resolution::FOUR_K,
+			comment.empty() ? "libdcp" : comment
 		);
 
+		if (enc.size() >= minimum_size) {
+			break;
+		}
+
+		/* The JPEG2000 is too low-bitrate for some decoders <cough>DSS200</cough> so add some noise
+		 * and try again.  This is slow but hopefully won't happen too often.  We have to do
+		 * convert_to_xyz() again because compress_j2k() corrupts its xyz parameter.
+		 */
+
+		xyz = convert_to_xyz (_frame, boost::bind(&Log::dcp_log, dcpomatic_log.get(), _1, _2));
+		auto size = xyz->size ();
+		auto pixels = size.width * size.height;
+		for (auto c = 0; c < 3; ++c) {
+			auto p = xyz->data(c);
+			for (auto i = 0; i < pixels; ++i) {
+				*p = std::min(4095, std::max(0, *p + rand() % 2));
+				++p;
+			}
+		}
+	}
+
 	switch (_frame->eyes()) {
 	case Eyes::BOTH:
 		LOG_DEBUG_ENCODE (N_("Finished locally-encoded frame %1 for mono"), _index);
diff --git a/test/low_bitrate_test.cc b/test/low_bitrate_test.cc
new file mode 100644
index 000000000..f7edecb62
--- /dev/null
+++ b/test/low_bitrate_test.cc
@@ -0,0 +1,47 @@
+/*
+    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/dcp_video.h"
+#include "lib/image.h"
+#include "lib/player_video.h"
+#include "lib/raw_image_proxy.h"
+extern "C" {
+#include <libavutil/pixfmt.h>
+}
+#include <boost/test/unit_test.hpp>
+#include <iostream>
+
+
+using std::make_shared;
+
+
+BOOST_AUTO_TEST_CASE (low_bitrate_test)
+{
+	auto image = make_shared<Image>(AV_PIX_FMT_RGB24, dcp::Size(1998, 1080), true);
+	image->make_black ();
+	auto proxy = make_shared<RawImageProxy>(image);
+	auto frame = make_shared<PlayerVideo>(proxy, Crop(), boost::optional<double>(), dcp::Size(1998, 1080), dcp::Size(1998, 1080), Eyes::BOTH, Part::WHOLE, boost::optional<ColourConversion>(), VideoRange::FULL, std::weak_ptr<Content>(), boost::optional<Frame>(), false);
+	auto dcp_video = make_shared<DCPVideo>(frame, 0, 24, 100000000, Resolution::TWO_K);
+	auto j2k = dcp_video->encode_locally();
+	BOOST_REQUIRE (j2k.size() >= 65536);
+}
+
+
diff --git a/test/wscript b/test/wscript
index f47eaea73..70aad81a3 100644
--- a/test/wscript
+++ b/test/wscript
@@ -94,6 +94,7 @@ def build(bld):
                  j2k_bandwidth_test.cc
                  job_test.cc
                  kdm_naming_test.cc
+                 low_bitrate_test.cc
                  markers_test.cc
                  no_use_video_test.cc
                  optimise_stills_test.cc
-- 
2.30.2