Introduce AudioDiscardHelper. Refactor audio decoders to use it.

media/base/audio_discard_helper.h

+// Copyright 2014 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.
+
+#ifndef MEDIA_BASE_AUDIO_DISCARD_HELPER_H_
+#define MEDIA_BASE_AUDIO_DISCARD_HELPER_H_
+
+#include "base/memory/ref_counted.h"
+#include "base/time/time.h"
+#include "media/base/audio_timestamp_helper.h"
+#include "media/base/buffers.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+class AudioBuffer;
+class DecoderBuffer;
+
+// Helper class for managing timestamps and discard events around decoding.
+class MEDIA_EXPORT AudioDiscardHelper {
+ public:
+  explicit AudioDiscardHelper(int sample_rate);
+  ~AudioDiscardHelper();
+
+  // Converts a TimeDelta to a frame count based on the constructed sample rate.
+  // |duration| must be positive.
+  size_t TimeDeltaToFrames(base::TimeDelta duration) const;
+
+  // Resets internal state and indicates that |initial_discard| of upcoming
+  // frames should be discarded.
+  void Reset(size_t initial_discard);
+
+  // Applies discard padding from the encoded buffer along with any initial
+  // discards.  |decoded_buffer| may be NULL, if not the timestamp and duration
+  // will be set after discards are applied.  Returns true if |decoded_buffer|
+  // exists after processing discard events.  Returns false if |decoded_buffer|
+  // was NULL, is completely discarded, or a processing error occurs.
+  //
+  // If AudioDiscardHelper is not initialized() the timestamp of the first
+  // |encoded_buffer| will be used as the basis for all future timestamps set on
+  // |decoded_buffer|s.  If the first buffer has a negative timestamp it will be
+  // clamped to zero.
+  bool ProcessBuffers(const scoped_refptr<DecoderBuffer>& encoded_buffer,
+                      const scoped_refptr<AudioBuffer>& decoded_buffer);
+
+  // Whether any buffers have been processed.
+  bool initialized() const {
+    return timestamp_helper_.base_timestamp() != kNoTimestamp();
+  }
+
+ private:
+  const int sample_rate_;
+  AudioTimestampHelper timestamp_helper_;
+
+  size_t discard_frames_;
+  base::TimeDelta last_input_timestamp_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(AudioDiscardHelper);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_DISCARD_HELPER_H_