Add an initial revision of an audio server.

services/media/audio/audio_pipe.h

Index: services/media/audio/audio_pipe.h
diff --git a/services/media/audio/audio_pipe.h b/services/media/audio/audio_pipe.h
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+++ b/services/media/audio/audio_pipe.h
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+// Copyright 2015 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 SERVICES_MEDIA_AUDIO_AUDIO_PIPE_H_
+#define SERVICES_MEDIA_AUDIO_AUDIO_PIPE_H_
+
+#include <memory>
+#include <vector>
+
+#include "mojo/services/media/common/cpp/linear_transform.h"
+#include "services/media/audio/fwd_decls.h"
+#include "services/media/common/media_pipe_base.h"
+
+namespace mojo {
+namespace media {
+namespace audio {
+
+class AudioPipe : public MediaPipeBase {
+ public:
+  class AudioPacketRef;
+  using AudioPacketRefPtr = std::shared_ptr<AudioPacketRef>;
+  using MediaPacketStatePtr = MediaPipeBase::MediaPacketStatePtr;
+
+  class AudioPacketRef {
+   public:
+    struct Region {
+      Region(const void* b, uint32_t ffl) : base(b), frac_frame_len(ffl) {}
+      const void* base;
+      uint32_t frac_frame_len;
+    };
+
+    ~AudioPacketRef();
+
+    const MediaPacketPtr& GetPacket() const { return state_->GetPacket(); }
+    void SetResult(MediaResult result) { return state_->SetResult(result); }
+
+    // Accessors for starting and ending presentation time stamps expressed in
+    // units of audio frames (note, not media time), as signed 51.12 fixed point
+    // integers (see AudioTrackImpl:PTS_FRACTIONAL_BITS).  At 192KHz, this
+    // allows for ~372.7 years of usable range when starting from a media time
+    // of 0.
+    //
+    // AudioPackets consumed by the AudioServer are all expected to have
+    // explicit presentation time stamps.  If packets sent by the user are
+    // missing timestamps, appropriate timestamps will be synthesized at this
+    // point in the pipeline.
+    //
+    // Note, the start pts is the time at which the first frame of audio in the
+    // packet should be presented.  The end_pts is the time at which the frame
+    // after the final frame in the packet would be presented.
+    //
+    // TODO(johngro): Reconsider this.  It may be best to keep things expressed
+    // simply in media time instead of converting to fractional units of track
+    // frames.  If/when outputs move away from a single fixed step size for
+    // output sampling, it will probably be best to just convert this back to
+    // media time.
+    const int64_t& start_pts() const { return start_pts_; }
+    const int64_t& end_pts() const { return end_pts_; }
+
+    // Accessor for the regions in the shared buffer which contain the actual
+    // sample data.
+    const std::vector<Region>& regions() const { return  regions_; }
+
+   private:
+    friend class AudioPipe;
+    AudioPacketRef(MediaPacketStatePtr state,
+                   AudioServerImpl* server,
+                   std::vector<Region>&& regions,  // NOLINT(build/c++11)
+                   int64_t start_pts,
+                   int64_t end_pts);
+
+    MediaPacketStatePtr state_;
+    AudioServerImpl* server_;
+
+    std::vector<Region> regions_;
+    int64_t start_pts_;
+    int64_t end_pts_;
+  };
+
+  AudioPipe(AudioTrackImpl* owner, AudioServerImpl* server);
+  ~AudioPipe() override;
+
+ protected:
+  void OnPacketReceived(MediaPacketStatePtr state) override;
+  void OnFlushRequested(const FlushCallback& cbk) override;
+
+ private:
+  AudioTrackImpl* owner_;
+  AudioServerImpl* server_;
+
+  // State used for timestamp interpolation
+  bool next_pts_known_ = 0;
+  int64_t next_pts_;
+};
+
+}  // namespace audio
+}  // namespace media
+}  // namespace mojo
+
+#endif  // SERVICES_MEDIA_AUDIO_AUDIO_PIPE_H_