Refactored AudioRendererImpl and NullAudioRenderer into a new base class AudioRendererBase.

AudioRendererBase handles the threaded queueing of audio data and provides simplified interfaces and methods for subclasses.

As the saying goes, "threads are hard" so reducing the amount of multi-threaded code people have to write is always a good thing.

Review URL: http://codereview.chromium.org/28042

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@10309 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 109 insertions, 0 deletions

diff --git a/media/filters/audio_renderer_base.h b/media/filters/audio_renderer_base.h
new file mode 100644
index 0000000..fc0b13b
--- /dev/null
+++ b/media/filters/audio_renderer_base.h
@@ -0,0 +1,109 @@
+// Copyright (c) 2009 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.
+
+// AudioRendererBase takes care of the tricky queuing work and provides simple
+// methods for subclasses to peek and poke at audio data.  In addition to
+// AudioRenderer interface methods this classes doesn't implement, subclasses
+// must also implement the following methods:
+//   OnInitialized
+//   OnStop
+//
+// The general assumption is that subclasses start a callback-based audio thread
+// which needs to be filled with decoded audio data.  AudioDecoderBase provides
+// FillBuffer which handles filling the provided buffer, dequeuing items,
+// scheduling additional reads and updating the clock.  In a sense,
+// AudioRendererBase is the producer and the subclass is the consumer.
+
+#ifndef MEDIA_FILTERS_AUDIO_RENDERER_BASE_H_
+#define MEDIA_FILTERS_AUDIO_RENDERER_BASE_H_
+
+#include <deque>
+
+#include "base/lock.h"
+#include "media/base/buffers.h"
+#include "media/base/factory.h"
+#include "media/base/filters.h"
+
+namespace media {
+
+class AudioRendererBase : public AudioRenderer {
+ public:
+  // MediaFilter implementation.
+  virtual void Stop();
+
+  // AudioRenderer implementation.
+  virtual bool Initialize(AudioDecoder* decoder);
+
+  // AssignableBuffer<AudioRendererBase, BufferInterface> implementation.
+  void OnAssignment(Buffer* buffer_in);
+
+ protected:
+  // The default maximum size of the queue.
+  static const size_t kDefaultMaxQueueSize;
+
+  // Only allow a factory to create this class.
+  AudioRendererBase(size_t max_queue_size);
+  virtual ~AudioRendererBase();
+ 
+  // Called by Initialize().  |media_format| is the format of the AudioDecoder.
+  // Subclasses should return true if they were able to initialize, false
+  // otherwise.
+  virtual bool OnInitialize(const MediaFormat* media_format) = 0;
+
+  // Called by Stop().  Subclasses should perform any necessary cleanup during
+  // this time, such as stopping any running threads.
+  virtual void OnStop() = 0;
+
+  // Fills the given buffer with audio data by dequeuing buffers and copying the
+  // data into the |dest|.  FillBuffer also takes care of updating the clock.
+  // Returns the number of bytes copied into |dest|, which may be less than
+  // equal to |len|.
+  //
+  // If this method is returns less bytes than |len| (including zero), it could
+  // be a sign that the pipeline is stalled or unable to stream the data fast
+  // enough.  In such scenarios, the callee should zero out unused portions
+  // of their buffer to playback silence.
+  //
+  // Safe to call on any thread.
+  size_t FillBuffer(uint8* dest, size_t len);
+
+  // Helper to parse a media format and return whether we were successful
+  // retrieving all the information we care about.
+  static bool ParseMediaFormat(const MediaFormat* media_format,
+                               int* channels_out, int* sample_rate_out,
+                               int* sample_bits_out);
+
+ private:
+  // Audio decoder.
+  AudioDecoder* decoder_;
+
+  // Maximum queue size, configuration parameter passed in during construction.
+  size_t max_queue_size_;
+
+  // Queued audio data.
+  typedef std::deque<Buffer*> BufferQueue;
+  BufferQueue queue_;
+  Lock lock_;
+
+  // Remembers the amount of remaining audio data for the front buffer.
+  size_t data_offset_;
+
+  // Whether or not we're initialized.
+  bool initialized_;
+
+  // Whether or not we've stopped.
+  bool stopped_;
+
+  // Posts a task on the pipeline thread to read a sample from the decoder.  The
+  // resulting buffer will be placed in the queue.
+  //
+  // Safe to call on any thread.
+  void ScheduleRead();
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererBase);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_AUDIO_RENDERER_BASE_H_