From b74e511f297624a940135787e8ec76bbc15f2d96 Mon Sep 17 00:00:00 2001
From: KongQun Yang <kqyang@google.com>
Date: Wed, 17 Jan 2018 17:26:03 -0800
Subject: [PATCH] Workaround for possible rounding errors in MSE

There could be rounding errors in MSE which could cut the first key
frame of the representation and thus cut all the frames until the next
key frame, which then leads to a big gap in presentation
timeline which stalls playback.

Adjusting presentationTimeOffset (PTO) by -1, i.e. backing off PTO by 1
to compensate for the possible rounding error. It should not cause any
playback issues as it is small enough. The workaround can be removed
once the problem is handled in all players.

The PTO adjustment is configurable with command line flag:
 --pto_adjustment, with value set to -1 by default.

b/71808910

Change-Id: I9c4d1e2ee84008b859a3638a8146c910cead1f15
---
 packager/mpd/base/simple_mpd_notifier.cc      | 21 +++++++++++++++++--
 .../mpd/base/simple_mpd_notifier_unittest.cc  | 10 ++++++---
 packager/mpd/mpd.gyp                          |  2 ++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/packager/mpd/base/simple_mpd_notifier.cc b/packager/mpd/base/simple_mpd_notifier.cc
index 9faa0bb73e..1449ad9e3d 100644
--- a/packager/mpd/base/simple_mpd_notifier.cc
+++ b/packager/mpd/base/simple_mpd_notifier.cc
@@ -6,6 +6,8 @@
 
 #include "packager/mpd/base/simple_mpd_notifier.h"
 
+#include <gflags/gflags.h>
+
 #include "packager/base/logging.h"
 #include "packager/base/stl_util.h"
 #include "packager/mpd/base/adaptation_set.h"
@@ -15,6 +17,17 @@
 #include "packager/mpd/base/period.h"
 #include "packager/mpd/base/representation.h"
 
+DEFINE_int32(
+    pto_adjustment,
+    -1,
+    "There could be rounding errors in MSE which could cut the first key frame "
+    "of the representation and thus cut all the frames until the next key "
+    "frame, which then leads to a big gap in presentation timeline which "
+    "stalls playback. A small back off may be necessary to compensate for the "
+    "possible rounding error. It should not cause any playback issues if it is "
+    "small enough. The workaround can be removed once the problem is handled "
+    "in all players.");
+
 namespace shaka {
 
 SimpleMpdNotifier::SimpleMpdNotifier(const MpdOptions& mpd_options)
@@ -151,9 +164,13 @@ Representation* SimpleMpdNotifier::AddRepresentationToPeriod(
 
   Representation* representation = nullptr;
   if (original_representation) {
+    uint64_t presentation_time_offset =
+        period->start_time_in_seconds() * media_info.reference_time_scale();
+    if (presentation_time_offset > 0) {
+      presentation_time_offset += FLAGS_pto_adjustment;
+    }
     representation = adaptation_set->CopyRepresentationWithTimeOffset(
-        *original_representation,
-        period->start_time_in_seconds() * media_info.reference_time_scale());
+        *original_representation, presentation_time_offset);
   } else {
     representation = adaptation_set->AddRepresentation(media_info);
   }
diff --git a/packager/mpd/base/simple_mpd_notifier_unittest.cc b/packager/mpd/base/simple_mpd_notifier_unittest.cc
index 8469b7c1c4..3c212a44a3 100644
--- a/packager/mpd/base/simple_mpd_notifier_unittest.cc
+++ b/packager/mpd/base/simple_mpd_notifier_unittest.cc
@@ -4,6 +4,7 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
+#include <gflags/gflags.h>
 #include <gmock/gmock.h>
 #include <google/protobuf/util/message_differencer.h>
 #include <gtest/gtest.h>
@@ -16,6 +17,8 @@
 #include "packager/mpd/base/simple_mpd_notifier.h"
 #include "packager/mpd/test/mpd_builder_test_helper.h"
 
+DECLARE_int32(pto_adjustment);
+
 namespace shaka {
 
 using ::testing::_;
@@ -242,9 +245,10 @@ TEST_F(SimpleMpdNotifierTest, NotifyCueEvent) {
   EXPECT_CALL(*mock_period2,
               GetOrCreateAdaptationSet(EqualsProto(valid_media_info1_), _))
       .WillOnce(Return(mock_adaptation_set2.get()));
-  EXPECT_CALL(*mock_adaptation_set2,
-              CopyRepresentationWithTimeOffset(Ref(*mock_representation),
-                                               kCueEventTimestamp))
+  EXPECT_CALL(
+      *mock_adaptation_set2,
+      CopyRepresentationWithTimeOffset(
+          Ref(*mock_representation), kCueEventTimestamp + FLAGS_pto_adjustment))
       .WillOnce(Return(mock_representation2.get()));
   EXPECT_TRUE(notifier.NotifyCueEvent(container_id, kCueEventTimestamp));
 }
diff --git a/packager/mpd/mpd.gyp b/packager/mpd/mpd.gyp
index b5cd65a56d..a89a195652 100644
--- a/packager/mpd/mpd.gyp
+++ b/packager/mpd/mpd.gyp
@@ -57,6 +57,7 @@
         '../base/base.gyp:base',
         '../file/file.gyp:file',
         '../media/base/media_base.gyp:media_base',
+        '../third_party/gflags/gflags.gyp:gflags',
         '../third_party/libxml/libxml.gyp:libxml',
         '../version/version.gyp:version',
         'media_info_proto',
@@ -103,6 +104,7 @@
         '../media/test/media_test.gyp:run_tests_with_atexit_manager',
         '../testing/gmock.gyp:gmock',
         '../testing/gtest.gyp:gtest',
+        '../third_party/gflags/gflags.gyp:gflags',
         'mpd_builder',
         'mpd_mocks',
         'mpd_util',