Exposes a shlib interface for media/audio path.

chromecast/public/media/cast_audio_output_stream.h

+// 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 CHROMECAST_PUBLIC_CAST_AUDIO_OUTPUT_STREAM_H_
+#define CHROMECAST_PUBLIC_CAST_AUDIO_OUTPUT_STREAM_H_
+
+#include <stdint.h>
+
+namespace chromecast {
+namespace media {
+
+// A simple struct describing an audio stream.
+struct AudioParameters {
+  int sample_rate;        // Sampling frequency/rate.
+  int bits_per_sample;    // Number of bits per sample.
+  int frames_per_buffer;  // Number of frames in a buffer.
+  int channels;           // Number of channels.
+
+  static const int kMaxSampleRate = 192000;
+  static const int kMaxBitsPerSample = 32;
+  static const int kMaxFramesPerBuffer = kMaxSampleRate;
+  static const int kMaxChannels = 32;  // The maximum number of channels.
+};
+
+// This is an interface for a Cast audio output stream. Implementations of this
+// interface are responsible for making calls to an AudioSourceCallback.
+class CastAudioOutputStream {
+ public:
+  // Audio sources must implement AudioSourceCallback. Calls to this interface
+  // must be made on the same thread on which the stream object is created.
+  class AudioSourceCallback {
+   public:
+    virtual ~AudioSourceCallback() {}

[byungchul, 2015/07/29 20:18:49]

It should be protected since CastAudioOutputStream doesn't take the ownership.

[slan, 2015/07/30 21:00:42]

Done.

+
+    // The CastAudioOutputStream calls this to request more data from the
+    // source. This method fills |dest| with |frames| frames of interleaved
+    // data, which takes the following struture for N channels:
+    //
+    //   [ch0, ch1, ..., chN, ch0, ch1, ..., chN, ...]
+    //   |<---- Frame 0 ---->|<---- Frame 1 ---->|...|
+    //
+    // |len| is the size of |dest| in bytes, and must satisfy the following:
+    //
+    //   |len| >= |frames| * (num channels) * (bytes per sample)
+    //
+    // where bytes per sample and channels are properties of the stream. These
+    // can be detemined through GetParameters(). |total_bytes_delay| contains
+    // the current number of bytes of delay buffered by the
+    // CastAudioOutputStream. Returns the number of frames successfully filled.
+    virtual int GetMoreData(void* dest,
+                            uint32_t len,
+                            int32_t frames,
+                            uint32_t total_bytes_delay) = 0;
+
+    // There was an error while playing a buffer. Audio source cannot be
+    // destroyed yet. No direct action needed by the AudioStream, but it is
+    // a good place to stop accumulating sound data since is is likely that
+    // playback will not continue.
+    virtual void OnError(CastAudioOutputStream* stream) = 0;
+  };
+
+  virtual ~CastAudioOutputStream() {}
+
+  // Returns the parameters describing the stream.
+  virtual const AudioParameters GetParameters() const = 0;

[byungchul, 2015/07/29 20:18:49]

const function would be too restricted as a shlib api.
 

[slan, 2015/07/30 21:00:42]

Done.

+
+  // Open the stream. A call to this method must always be followed by a call to

[halliwell, 2015/07/29 22:10:14]

This comment is written from the POV of us (clients of the API).  I think we try
to phrase vendor interfaces from their POV.  i.e. "this method will always be
followed by a call to Close".

[slan, 2015/07/30 21:00:42]

Done.

+  // Close() even if Open() fails. This method may block the caller's thread.
+  virtual bool Open() = 0;
+
+  // Starts playing audio and generating AudioSourceCallback::GetMoreData().
+  // Since implementor of CastAudioOutputStream may have internal buffers, right
+  // after calling this method initial buffers are fetched.
+  //
+  // The output stream does not take ownership of this callback.
+  virtual void Start(AudioSourceCallback* callback) = 0;
+
+  // Stops playing audio. Effect might not be instantaneous as the hardware
+  // might have locked audio data that is processing.
+  virtual void Stop() = 0;
+
+  // Sets the relative volume, with range [0.0, 1.0] inclusive.
+  virtual void SetVolume(double volume) = 0;
+
+  // Gets the relative volume, with range [0.0, 1.0] inclusive. This method may
+  // be .
+  virtual double GetVolume() = 0;
+
+  // Close the stream. This also generates AudioSourceCallback::OnClose().
+  // After calling this method, the object should not be used anymore. Like all
+  // other methods, this must be made on the same thread on which the stream was
+  // created.
+  virtual void Close() = 0;
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_PUBLIC_CAST_AUDIO_OUTPUT_STREAM_H_