Add new class AudioBufferQueue.

media/base/audio_buffer_queue.cc

+// Copyright 2013 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/base/audio_buffer_queue.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "media/base/audio_bus.h"
+#include "media/base/buffers.h"
+
+namespace media {
+
+AudioBufferQueue::AudioBufferQueue() { Clear(); }
+AudioBufferQueue::~AudioBufferQueue() {}
+
+void AudioBufferQueue::Clear() {
+  buffers_.clear();
+  current_buffer_ = buffers_.begin();
+  current_buffer_offset_ = 0;
+  frames_ = 0;
+  current_time_ = kNoTimestamp();
+}
+
+void AudioBufferQueue::Append(const scoped_refptr<AudioBuffer>& buffer_in) {
+  // If we have just written the first buffer, update |current_time_| to be the
+  // start time.
+  if (buffers_.empty()) {
+    DCHECK_EQ(frames_, 0);
+    current_time_ = buffer_in->timestamp();
+  }
+
+  // Add the buffer to the queue. Inserting into deque invalidates all
+  // iterators, so point to the first buffer.
+  buffers_.push_back(buffer_in);
+  current_buffer_ = buffers_.begin();
+
+  // Update the |frames_| counter since we have added frames.
+  frames_ += buffer_in->frame_count();
+  CHECK_GT(frames_, 0);  // make sure it doesn't overflow.
+}
+
+int AudioBufferQueue::ReadFrames(int frames, AudioBus* dest) {
+  DCHECK_GE(dest->frames(), frames);
+  return InternalRead(frames, true, 0, dest);
+}
+
+int AudioBufferQueue::PeekFrames(int frames,
+                                 int forward_offset,
+                                 AudioBus* dest) {
+  DCHECK_GE(dest->frames(), frames);
+  return InternalRead(frames, false, forward_offset, dest);
+}
+
+void AudioBufferQueue::SeekFrames(int frames) {
+  // Perform seek only if we have enough bytes in the queue.
+  CHECK_LE(frames, frames_);
+  int taken = InternalRead(frames, true, 0, NULL);
+  DCHECK_EQ(taken, frames);
+}
+
+int AudioBufferQueue::InternalRead(int frames,
+                                   bool advance_position,
+                                   int forward_offset,
+                                   AudioBus* dest) {
+  // Counts how many frames are actually read from the buffer queue.
+  int taken = 0;
+  BufferQueue::iterator current_buffer = current_buffer_;
+  int current_buffer_offset = current_buffer_offset_;
+
+  int frames_to_skip = forward_offset;
+  while (taken < frames) {
+    // |current_buffer| is valid since the first time this buffer is appended
+    // with data. Make sure there is data to be processed.
+    if (current_buffer == buffers_.end())
+      break;
+
+    scoped_refptr<AudioBuffer> buffer = *current_buffer;
+
+    int remaining_frames_in_buffer =
+        buffer->frame_count() - current_buffer_offset;
+
+    if (frames_to_skip > 0) {
+      // If there are frames to skip, do it first. May need to skip into
+      // subsequent buffers.
+      int skipped = std::min(remaining_frames_in_buffer, frames_to_skip);
+      current_buffer_offset += skipped;
+      frames_to_skip -= skipped;
+    } else {
+      // Find the right amount to copy from the current buffer. We shall copy no
+      // more than |frames| frames in total and each single step copies no more
+      // than the current buffer size.
+      int copied = std::min(frames - taken, remaining_frames_in_buffer);
+
+      // if |dest| is NULL, there's no need to copy.
+      if (dest)
+        buffer->ReadFrames(copied, current_buffer_offset, taken, dest);
+
+      // Increase total number of frames copied, which regulates when to end
+      // this loop.
+      taken += copied;
+
+      // We have read |copied| frames from the current buffer. Advance the
+      // offset.
+      current_buffer_offset += copied;
+    }
+
+    // Has the buffer has been consumed?
+    if (current_buffer_offset == buffer->frame_count()) {
+      if (advance_position) {
+        // Next buffer may not have timestamp, so we need to update current
+        // timestamp before switching to the next buffer.
+        UpdateCurrentTime(current_buffer, current_buffer_offset);
+      }
+
+      // If we are at the last buffer, no more data to be copied, so stop.
+      BufferQueue::iterator next = current_buffer + 1;
+      if (next == buffers_.end())
+        break;
+
+      // Advances the iterator.
+      current_buffer = next;
+      current_buffer_offset = 0;
+    }
+  }
+
+  if (advance_position) {
+    // Update the appropriate values since |taken| frames have been copied out.
+    frames_ -= taken;
+    DCHECK_GE(frames_, 0);
+    DCHECK(current_buffer_ != buffers_.end() || frames_ == 0);
+
+    current_buffer_ = current_buffer;
+    current_buffer_offset_ = current_buffer_offset;
+
+    UpdateCurrentTime(current_buffer_, current_buffer_offset_);
+
+    // Remove any buffers before the current buffer as there is no going
+    // backwards.
+    buffers_.erase(buffers_.begin(), current_buffer_);
+  }
+
+  return taken;
+}
+
+void AudioBufferQueue::UpdateCurrentTime(BufferQueue::iterator buffer,
+                                         int offset) {
+  if (buffer != buffers_.end() && (*buffer)->timestamp() != kNoTimestamp()) {
+    double time_offset = ((*buffer)->duration().InMicroseconds() * offset) /
+                         static_cast<double>((*buffer)->frame_count());
+    current_time_ =
+        (*buffer)->timestamp() + base::TimeDelta::FromMicroseconds(
+                                     static_cast<int64>(time_offset + 0.5));
+  }
+}
+
+}  // namespace media