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