media/base/stream_parser.cc

   1 // Copyright (c) 2012 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 #include "media/base/stream_parser.h"
   6
   7 #include "media/base/buffers.h"
   8 #include "media/base/stream_parser_buffer.h"
   9
  10 namespace media {
  11
  12 StreamParser::InitParameters::InitParameters(base::TimeDelta duration)
  13     : duration(duration),
  14       auto_update_timestamp_offset(false),
  15       liveness(DemuxerStream::LIVENESS_UNKNOWN) {
  16 }
  17
  18 StreamParser::StreamParser() {}
  19
  20 StreamParser::~StreamParser() {}
  21
  22 static bool MergeBufferQueuesInternal(
  23     const std::vector<const StreamParser::BufferQueue*>& buffer_queues,
  24     StreamParser::BufferQueue* merged_buffers) {
  25   // Instead of std::merge usage, this method implements a custom merge because:
  26   // 1) |buffer_queues| may contain N queues,
  27   // 2) we must detect and return false if any of the queues in |buffer_queues|
  28   // is unsorted, and
  29   // 3) we must detect and return false if any of the buffers in |buffer_queues|
  30   // has a decode timestamp prior to the last, if any, buffer in
  31   // |merged_buffers|.
  32   // TODO(wolenetz/acolwell): Refactor stream parsers to eliminate need for
  33   // this large grain merge. See http://crbug.com/338484.
  34
  35   // Done if no inputs to merge.
  36   if (buffer_queues.empty())
  37     return true;
  38
  39   // Build a vector of iterators, one for each input, to traverse inputs.
  40   // The union of these iterators points to the set of candidate buffers
  41   // for being appended to |merged_buffers|.
  42   size_t num_itrs = buffer_queues.size();
  43   std::vector<StreamParser::BufferQueue::const_iterator> itrs(num_itrs);
  44   for (size_t i = 0; i < num_itrs; ++i)
  45     itrs[i] = buffer_queues[i]->begin();
  46
  47   // |last_decode_timestamp| tracks the lower bound, if any, that all candidate
  48   // buffers must not be less than. If |merged_buffers| already has buffers,
  49   // initialize |last_decode_timestamp| to the decode timestamp of the last
  50   // buffer in it.
  51   DecodeTimestamp last_decode_timestamp = kNoDecodeTimestamp();
  52   if (!merged_buffers->empty())
  53     last_decode_timestamp = merged_buffers->back()->GetDecodeTimestamp();
  54
  55   // Repeatedly select and append the next buffer from the candidate buffers
  56   // until either:
  57   // 1) returning false, to indicate detection of decreasing DTS in some queue,
  58   //    when a candidate buffer has decode timestamp below
  59   //    |last_decode_timestamp|, which means either an input buffer wasn't
  60   //    sorted correctly or had a buffer with decode timestamp below the last
  61   //    buffer, if any, in |merged_buffers|, or
  62   // 2) returning true when all buffers have been merged successfully;
  63   //    equivalently, when all of the iterators in |itrs| have reached the end
  64   //    of their respective queue from |buffer_queues|.
  65   // TODO(wolenetz/acolwell): Ideally, we would use a heap to store the head of
  66   // all queues and pop the head with lowest decode timestamp in log(N) time.
  67   // However, N will typically be small and usage of this implementation is
  68   // meant to be short-term. See http://crbug.com/338484.
  69   while (true) {
  70     // Tracks which queue's iterator is pointing to the candidate buffer to
  71     // append next, or -1 if no candidate buffers found. This indexes |itrs|.
  72     int index_of_queue_with_next_decode_timestamp = -1;
  73     DecodeTimestamp next_decode_timestamp = kNoDecodeTimestamp();
  74
  75     // Scan each of the iterators for |buffer_queues| to find the candidate
  76     // buffer, if any, that has the lowest decode timestamp.
  77     for (size_t i = 0; i < num_itrs; ++i) {
  78       if (itrs[i] == buffer_queues[i]->end())
  79         continue;
  80
  81       // Extract the candidate buffer's decode timestamp.
  82       DecodeTimestamp ts = (*itrs[i])->GetDecodeTimestamp();
  83
  84       if (last_decode_timestamp != kNoDecodeTimestamp() &&
  85           ts < last_decode_timestamp)
  86         return false;
  87
  88       if (ts < next_decode_timestamp ||
  89           next_decode_timestamp == kNoDecodeTimestamp()) {
  90         // Remember the decode timestamp and queue iterator index for this
  91         // potentially winning candidate buffer.
  92         next_decode_timestamp = ts;
  93         index_of_queue_with_next_decode_timestamp = i;
  94       }
  95     }
  96
  97     // All done if no further candidate buffers exist.
  98     if (index_of_queue_with_next_decode_timestamp == -1)
  99       return true;
 100
 101     // Otherwise, append the winning candidate buffer to |merged_buffers|,
 102     // remember its decode timestamp as |last_decode_timestamp| now that it is
 103     // the last buffer in |merged_buffers|, advance the corresponding
 104     // input BufferQueue iterator, and continue.
 105     scoped_refptr<StreamParserBuffer> buffer =
 106         *itrs[index_of_queue_with_next_decode_timestamp];
 107     last_decode_timestamp = buffer->GetDecodeTimestamp();
 108     merged_buffers->push_back(buffer);
 109     ++itrs[index_of_queue_with_next_decode_timestamp];
 110   }
 111 }
 112
 113 bool MergeBufferQueues(const StreamParser::BufferQueue& audio_buffers,
 114                        const StreamParser::BufferQueue& video_buffers,
 115                        const StreamParser::TextBufferQueueMap& text_buffers,
 116                        StreamParser::BufferQueue* merged_buffers) {
 117   DCHECK(merged_buffers);
 118
 119   // Prepare vector containing pointers to any provided non-empty buffer queues.
 120   std::vector<const StreamParser::BufferQueue*> buffer_queues;
 121   if (!audio_buffers.empty())
 122     buffer_queues.push_back(&audio_buffers);
 123   if (!video_buffers.empty())
 124     buffer_queues.push_back(&video_buffers);
 125   for (StreamParser::TextBufferQueueMap::const_iterator map_itr =
 126            text_buffers.begin();
 127        map_itr != text_buffers.end();
 128        map_itr++) {
 129     if (!map_itr->second.empty())
 130       buffer_queues.push_back(&(map_itr->second));
 131   }
 132
 133   // Do the merge.
 134   return MergeBufferQueuesInternal(buffer_queues, merged_buffers);
 135 }
 136
 137 }  // namespace media