Add a wrapper class for SampleToGroup iterator

SampleToGroupIterator provides convenient functions to iterate through
the compressed SampleToGroup table.

BUG=367366

Review URL: https://codereview.chromium.org/263763006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269031 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 164 insertions, 0 deletions

diff --git a/media/formats/mp4/sample_to_group_iterator.cc b/media/formats/mp4/sample_to_group_iterator.cc
new file mode 100644
index 0000000..01c7072
--- /dev/null
+++ b/media/formats/mp4/sample_to_group_iterator.cc
@@ -0,0 +1,47 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/formats/mp4/sample_to_group_iterator.h"
+
+#include "base/logging.h"
+
+namespace media {
+namespace mp4 {
+
+SampleToGroupIterator::SampleToGroupIterator(
+    const SampleToGroup& sample_to_group)
+    : remaining_samples_(0),
+      sample_to_group_table_(sample_to_group.entries),
+      iterator_(sample_to_group_table_.begin()) {
+  // Handle the case that the table contains an entry with sample count 0.
+  while (iterator_ != sample_to_group_table_.end()) {
+    remaining_samples_ = iterator_->sample_count;
+    if (remaining_samples_ > 0)
+      break;
+    ++iterator_;
+  }
+}
+
+SampleToGroupIterator::~SampleToGroupIterator() {}
+
+bool SampleToGroupIterator::Advance() {
+  DCHECK(IsValid());
+
+  --remaining_samples_;
+  // Handle the case that the table contains an entry with sample count 0.
+  while (remaining_samples_ == 0) {
+    ++iterator_;
+    if (iterator_ == sample_to_group_table_.end())
+      return false;
+    remaining_samples_ = iterator_->sample_count;
+  }
+  return true;
+}
+
+bool SampleToGroupIterator::IsValid() const {
+  return remaining_samples_ > 0;
+}
+
+}  // namespace mp4
+}  // namespace media
diff --git a/media/formats/mp4/sample_to_group_iterator.h b/media/formats/mp4/sample_to_group_iterator.h
new file mode 100644
index 0000000..c2ea60f
--- /dev/null
+++ b/media/formats/mp4/sample_to_group_iterator.h
@@ -0,0 +1,49 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_FORMATS_MP4_SAMPLE_TO_GROUP_ITERATOR_H_
+#define MEDIA_FORMATS_MP4_SAMPLE_TO_GROUP_ITERATOR_H_
+
+#include <vector>
+
+#include "media/formats/mp4/box_definitions.h"
+
+namespace media {
+namespace mp4 {
+
+// Sample To Group Box ('sbgp') can be used to find the group that a sample
+// belongs to and the associated description of that sample group. It is
+// compactly coded though. This class implements the iterator to iterate
+// through the compressed table to get the associated sample group description
+// index.
+class MEDIA_EXPORT SampleToGroupIterator {
+ public:
+  explicit SampleToGroupIterator(const SampleToGroup& sample_to_group);
+  ~SampleToGroupIterator();
+
+  // Advances the iterator to refer to the next sample. Return status
+  // indicating whether the sample is still valid.
+  bool Advance();
+
+  // Returns whether the current sample is valid.
+  bool IsValid() const;
+
+  // Returns group description index for current sample.
+  uint32 group_description_index() const {
+    return iterator_->group_description_index;
+  }
+
+ private:
+  // Track how many samples remaining for current table entry.
+  uint32 remaining_samples_;
+  const std::vector<SampleToGroupEntry>& sample_to_group_table_;
+  std::vector<SampleToGroupEntry>::const_iterator iterator_;
+
+  DISALLOW_COPY_AND_ASSIGN(SampleToGroupIterator);
+};
+
+}  // namespace mp4
+}  // namespace media
+
+#endif  // MEDIA_FORMATS_MP4_SAMPLE_TO_GROUP_ITERATOR_H_
diff --git a/media/formats/mp4/sample_to_group_iterator_unittest.cc b/media/formats/mp4/sample_to_group_iterator_unittest.cc
new file mode 100644
index 0000000..3e8148c
--- /dev/null
+++ b/media/formats/mp4/sample_to_group_iterator_unittest.cc
@@ -0,0 +1,65 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/formats/mp4/sample_to_group_iterator.h"
+
+#include "base/memory/scoped_ptr.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace media {
+namespace mp4 {
+
+namespace {
+const SampleToGroupEntry kCompactSampleToGroupTable[] =
+    {{10, 8}, {9, 5}, {25, 7}, {48, 63}, {8, 2}};
+}  // namespace
+
+class SampleToGroupIteratorTest : public testing::Test {
+ public:
+  SampleToGroupIteratorTest() {
+    // Build sample group description index table from kSampleToGroupTable.
+    for (size_t i = 0; i < arraysize(kCompactSampleToGroupTable); ++i) {
+      for (uint32 j = 0; j < kCompactSampleToGroupTable[i].sample_count; ++j) {
+        sample_to_group_table_.push_back(
+            kCompactSampleToGroupTable[i].group_description_index);
+      }
+    }
+
+    sample_to_group_.entries.assign(
+        kCompactSampleToGroupTable,
+        kCompactSampleToGroupTable + arraysize(kCompactSampleToGroupTable));
+    sample_to_group_iterator_.reset(
+        new SampleToGroupIterator(sample_to_group_));
+  }
+
+ protected:
+  std::vector<uint32> sample_to_group_table_;
+  SampleToGroup sample_to_group_;
+  scoped_ptr<SampleToGroupIterator> sample_to_group_iterator_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SampleToGroupIteratorTest);
+};
+
+TEST_F(SampleToGroupIteratorTest, EmptyTable) {
+  SampleToGroup sample_to_group;
+  SampleToGroupIterator iterator(sample_to_group);
+  EXPECT_FALSE(iterator.IsValid());
+}
+
+TEST_F(SampleToGroupIteratorTest, Advance) {
+  ASSERT_EQ(sample_to_group_table_[0],
+            sample_to_group_iterator_->group_description_index());
+  for (uint32 sample = 1; sample < sample_to_group_table_.size(); ++sample) {
+    ASSERT_TRUE(sample_to_group_iterator_->Advance());
+    ASSERT_EQ(sample_to_group_table_[sample],
+              sample_to_group_iterator_->group_description_index());
+    ASSERT_TRUE(sample_to_group_iterator_->IsValid());
+  }
+  ASSERT_FALSE(sample_to_group_iterator_->Advance());
+  ASSERT_FALSE(sample_to_group_iterator_->IsValid());
+}
+
+}  // namespace mp4
+}  // namespace media
diff --git a/media/media.gyp b/media/media.gyp
index 9da80d8..a799028 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -881,6 +881,8 @@
             'formats/mp4/es_descriptor.h',
             'formats/mp4/mp4_stream_parser.cc',
             'formats/mp4/mp4_stream_parser.h',
+            'formats/mp4/sample_to_group_iterator.cc',
+            'formats/mp4/sample_to_group_iterator.h',
             'formats/mp4/track_run_iterator.cc',
             'formats/mp4/track_run_iterator.h',
             'formats/mpeg/adts_constants.cc',
@@ -1175,6 +1177,7 @@
             'formats/mp4/box_reader_unittest.cc',
             'formats/mp4/es_descriptor_unittest.cc',
             'formats/mp4/mp4_stream_parser_unittest.cc',
+            'formats/mp4/sample_to_group_iterator_unittest.cc',
             'formats/mp4/track_run_iterator_unittest.cc',
             'formats/mpeg/adts_stream_parser_unittest.cc',
             'formats/mpeg/mp3_stream_parser_unittest.cc',