Use a predictable RNG when adding noise to low-bitrate images.

The recovery code assumes that encoding a given frame from the
same data will always give the same output; it always encodes frame 0
again to set things up properly and if that frame is a different size
to the previous run everything breaks.

6 files changed, 116 insertions, 21 deletions

diff --git a/src/lib/dcp_video.cc b/src/lib/dcp_video.cc
index 6bbd0d423..1f9f76771 100644
--- a/src/lib/dcp_video.cc
+++ b/src/lib/dcp_video.cc
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2012-2016 Carl Hetherington <cth@carlh.net>
+    Copyright (C) 2012-2021 Carl Hetherington <cth@carlh.net>
 
     This file is part of DCP-o-matic.
 
@@ -18,6 +18,7 @@
 
 */
 
+
 /** @file  src/dcp_video_frame.cc
  *  @brief A single frame of video destined for a DCP.
  *
@@ -28,17 +29,19 @@
  *  of images that require encoding.
  */
 
-#include "dcp_video.h"
+
+#include "compose.hpp"
 #include "config.h"
-#include "exceptions.h"
-#include "encode_server_description.h"
+#include "cross.h"
+#include "dcp_video.h"
+#include "dcpomatic_log.h"
 #include "dcpomatic_socket.h"
+#include "encode_server_description.h"
+#include "exceptions.h"
 #include "image.h"
 #include "log.h"
-#include "dcpomatic_log.h"
-#include "cross.h"
 #include "player_video.h"
-#include "compose.hpp"
+#include "rng.h"
 #include "warnings.h"
 #include <libcxml/cxml.h>
 #include <dcp/raw_convert.h>
@@ -143,6 +146,8 @@ DCPVideo::encode_locally ()
 			break;
 		}
 
+		LOG_GENERAL (N_("Frame %1 encoded size was small (%2); adding noise at level %3"), _index, enc.size(), noise_amount);
+
 		/* 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.
@@ -151,10 +156,11 @@ DCPVideo::encode_locally ()
 		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;
+		dcpomatic::RNG rng(42);
 		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() % noise_amount));
+				*p = std::min(4095, std::max(0, *p + (rng.get() % noise_amount)));
 				++p;
 			}
 		}
diff --git a/src/lib/rng.cc b/src/lib/rng.cc
new file mode 100644
index 000000000..3fc41725d
--- /dev/null
+++ b/src/lib/rng.cc
@@ -0,0 +1,42 @@
+/*
+    Copyright (C) 2020 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 "rng.h"
+#include <stdint.h>
+
+
+using namespace dcpomatic;
+
+
+RNG::RNG (int32_t seed)
+	: _state (static_cast<uint32_t>(seed))
+{
+
+}
+
+
+int32_t RNG::get ()
+{
+	uint32_t const b = ((_state >> 0) ^ (_state >> 1) ^ (_state >> 2) ^ (_state >> 7));
+	_state = (_state >> 1) | (b << 23);
+	return static_cast<int32_t>(_state);
+}
+
diff --git a/src/lib/rng.h b/src/lib/rng.h
new file mode 100644
index 000000000..f3349ce9b
--- /dev/null
+++ b/src/lib/rng.h
@@ -0,0 +1,44 @@
+/*
+    Copyright (C) 2020 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 <stdint.h>
+
+
+namespace dcpomatic {
+
+
+/** @class  RNG
+ *  @brief  Linear-feedback random number generator
+ */
+class RNG
+{
+public:
+	RNG (int32_t seed);
+
+	int32_t get ();
+
+private:
+	uint32_t _state;
+};
+
+
+}
+
diff --git a/src/lib/wscript b/src/lib/wscript
index bff3382e0..1b45152a4 100644
--- a/src/lib/wscript
+++ b/src/lib/wscript
@@ -144,6 +144,7 @@ sources = """
           render_text.cc
           resampler.cc
           rgba.cc
+          rng.cc
           scoped_temporary.cc
           scp_uploader.cc
           screen.cc
diff --git a/test/torture_test.cc b/test/torture_test.cc
index 232435363..434ed0b5e 100644
--- a/test/torture_test.cc
+++ b/test/torture_test.cc
@@ -234,7 +234,7 @@ BOOST_AUTO_TEST_CASE (torture_test1)
 
 	shared_ptr<dcp::MonoPictureAssetReader> picture_reader = picture->start_read ();
 
-	/* First 5 * 24 = 120 frames should be black */
+	/* First 5 * 24 = 120 frames should be black, possibly with a little noise to raise the bitrate */
 
 	shared_ptr<dcp::OpenJPEGImage> ref;
 	for (int i = 0; i < 120; ++i) {
@@ -242,15 +242,17 @@ BOOST_AUTO_TEST_CASE (torture_test1)
 		shared_ptr<dcp::OpenJPEGImage> image = fr->xyz_image ();
 		dcp::Size const size = image->size ();
 		if (i == 0) {
+			/* Check the first frame pixel by pixel... */
 			for (int c = 0; c < 3; ++c) {
 				for (int y = 0; y < size.height; ++y) {
 					for (int x = 0; x < size.width; ++x) {
-						BOOST_REQUIRE_EQUAL (image->data(c)[y * size.height + x], 0);
+						BOOST_REQUIRE (image->data(c)[y * size.height + x] <= 3);
 					}
 				}
 			}
 			ref = image;
 		} else {
+			/* ... then all the others should be the same */
 			for (int c = 0; c < 3; ++c) {
 				BOOST_REQUIRE_MESSAGE (
 					memcmp (image->data(c), ref->data(c), size.width * size.height * sizeof(int)) == 0,
@@ -260,7 +262,7 @@ BOOST_AUTO_TEST_CASE (torture_test1)
 		}
 	}
 
-	/* Then 24 red */
+	/* Then 24 red, perhaps also with some noise */
 
 	for (int i = 120; i < 144; ++i) {
 		shared_ptr<const dcp::MonoPictureFrame> fr = picture_reader->get_frame (i);
@@ -270,15 +272,15 @@ BOOST_AUTO_TEST_CASE (torture_test1)
 			for (int y = 0; y < size.height; ++y) {
 				for (int x = 0; x < size.width; ++x) {
 					BOOST_REQUIRE_MESSAGE (
-						abs(image->data(0)[y * size.height + x] - 2808) <= 2,
+						abs(image->data(0)[y * size.height + x] - 2808) <= 5,
 						"failed on frame " << i << " with image data " << image->data(0)[y * size.height + x]
 						);
 					BOOST_REQUIRE_MESSAGE (
-						abs(image->data(1)[y * size.height + x] - 2176) <= 2,
+						abs(image->data(1)[y * size.height + x] - 2176) <= 5,
 						"failed on frame " << i << " with image data " << image->data(1)[y * size.height + x]
 						);
 					BOOST_REQUIRE_MESSAGE (
-						abs(image->data(2)[y * size.height + x] - 865) <= 2,
+						abs(image->data(2)[y * size.height + x] - 865) <= 5,
 						"failed on frame " << i << " with image data " << image->data(2)[y * size.height + x]
 						);
 				}
diff --git a/test/video_level_test.cc b/test/video_level_test.cc
index 2461bb9b3..0de6e17b3 100644
--- a/test/video_level_test.cc
+++ b/test/video_level_test.cc
@@ -438,7 +438,7 @@ BOOST_AUTO_TEST_CASE (movie_V_to_dcp)
 	pair<int, int> range = dcp_range (movie_V("movie_V_to_dcp"));
 	/* Video range has been correctly expanded to full for the DCP */
 	BOOST_CHECK_EQUAL (range.first, 0);
-	BOOST_CHECK_EQUAL (range.second, 4082);
+	BOOST_CHECK_EQUAL (range.second, 4085);
 }
 
 
@@ -448,8 +448,8 @@ BOOST_AUTO_TEST_CASE (movie_VoF_to_dcp)
 	/* We said that video range data was really full range, so here we are in the DCP
 	 * with video-range data.
 	 */
-	BOOST_CHECK_EQUAL (range.first, 350);
-	BOOST_CHECK_EQUAL (range.second, 3832);
+	BOOST_CHECK_EQUAL (range.first, 348);
+	BOOST_CHECK_EQUAL (range.second, 3833);
 }
 
 
@@ -458,7 +458,7 @@ BOOST_AUTO_TEST_CASE (movie_F_to_dcp)
 	pair<int, int> range = dcp_range (movie_F("movie_F_to_dcp"));
 	/* The nearly-full-range of the input has been preserved */
 	BOOST_CHECK_EQUAL (range.first, 0);
-	BOOST_CHECK_EQUAL (range.second, 4082);
+	BOOST_CHECK_EQUAL (range.second, 4085);
 }
 
 
@@ -475,15 +475,15 @@ BOOST_AUTO_TEST_CASE (image_F_to_dcp)
 {
 	pair<int, int> range = dcp_range (image_F("image_F_to_dcp"));
 	BOOST_CHECK_EQUAL (range.first, 0);
-	BOOST_CHECK_EQUAL (range.second, 4081);
+	BOOST_CHECK_EQUAL (range.second, 4085);
 }
 
 
 BOOST_AUTO_TEST_CASE (image_FoV_to_dcp)
 {
 	pair<int, int> range = dcp_range (image_FoV("image_FoV_to_dcp"));
-	BOOST_CHECK_EQUAL (range.first, 431);
-	BOOST_CHECK_EQUAL (range.second, 4012);
+	BOOST_CHECK_EQUAL (range.first, 429);
+	BOOST_CHECK_EQUAL (range.second, 4014);
 }