media/base/text_ranges.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_BASE_TEXT_RANGES_H_
   6 #define MEDIA_BASE_TEXT_RANGES_H_
   7
   8 #include <map>
   9
  10 #include "base/macros.h"
  11 #include "base/time/time.h"
  12 #include "media/base/media_export.h"
  13
  14 namespace media {
  15
  16 // Helper class used by the TextRenderer to filter out text cues that
  17 // have already been passed downstream.
  18 class MEDIA_EXPORT TextRanges {
  19  public:
  20   TextRanges();
  21   ~TextRanges();
  22
  23   // Reset the current range pointer, such that we bind to a new range
  24   // (either one that exists already, or one that is freshly-created)
  25   // during the next AddCue().
  26   void Reset();
  27
  28   // Given a cue with starting timestamp |start_time|, add its start
  29   // time to the time ranges. (Note that following a Reset(), cue
  30   // times are assumed to be monotonically increasing.) If this time
  31   // has already been added to the time ranges, then AddCue() returns
  32   // false and clients should not push the cue downstream. Otherwise,
  33   // the time is added to the time ranges and AddCue() returns true,
  34   // meaning that the cue should be pushed downstream.
  35   bool AddCue(base::TimeDelta start_time);
  36
  37   // Returns a count of the number of time ranges, intended for use by
  38   // the unit test module to vet proper time range merge behavior.
  39   size_t RangeCountForTesting() const;
  40
  41  private:
  42   // Describes a range of times for cues that have already been
  43   // pushed downstream.
  44   class Range {
  45    public:
  46     // Initialize last_time count.
  47     void ResetCount(base::TimeDelta start_time);
  48
  49     // Set last_time and associated counts.
  50     void SetLastTime(base::TimeDelta last_time);
  51
  52     // Adjust time range state to mark the cue as having been seen,
  53     // returning true if we have not seen |start_time| already and
  54     // false otherwise.
  55     bool AddCue(base::TimeDelta start_time);
  56
  57     // Returns the value of the last time in the range.
  58     base::TimeDelta last_time() const;
  59
  60    private:
  61     // The last timestamp of this range.
  62     base::TimeDelta last_time_;
  63
  64     // The number of cues we have detected so far, for this range,
  65     // whose timestamp matches last_time.
  66     int max_count_;
  67
  68     // The number of cues we have seen since the most recent Reset(),
  69     // whose timestamp matches last_time.
  70     int count_;
  71   };
  72
  73   typedef std::map<base::TimeDelta, Range> RangeMap;
  74
  75   // NewRange() is used to create a new time range when AddCue() is
  76   // called immediately following a Reset(), and no existing time
  77   // range contains the indicated |start_time| of the cue.
  78   void NewRange(base::TimeDelta start_time);
  79
  80   // Coalesce curr_range with the range that immediately follows.
  81   void Merge(Range& curr_range, const RangeMap::iterator& next_range_itr);
  82
  83   // The collection of time ranges, each of which is bounded
  84   // (inclusive) by the key and Range::last_time.
  85   RangeMap range_map_;
  86
  87   // The time range to which we bind following a Reset().
  88   RangeMap::iterator curr_range_itr_;
  89
  90   DISALLOW_COPY_AND_ASSIGN(TextRanges);
  91 };
  92
  93 }  // namespace media
  94
  95 #endif  // MEDIA_BASE_TEXT_RANGES_H_