chromecast/public/cast_media_shlib.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_MEDIA_SHLIB_H_
#define CHROMECAST_PUBLIC_CAST_MEDIA_SHLIB_H_

#include <stdint.h>

#include <string>
#include <vector>

#include "chromecast_export.h"

namespace chromecast {
namespace media {

enum SampleFormat : int;

class MediaPipelineBackend;
struct MediaPipelineDeviceParams;
class VideoPlane;

// Provides access to platform-specific media systems and hardware resources.
// In cast_shell, all usage is from the browser process.  An implementation is
// assumed to be in an uninitialized state initially.  When uninitialized, no
// API calls will be made except for Initialize, which brings the implementation
// into an initialized state.  A call to Finalize returns the implementation to
// its uninitialized state.  The implementation must support multiple
// transitions between these states, to support resource grant/revoke events and
// also to allow multiple unit tests to bring up the media systems in isolation
// from other tests.
class CHROMECAST_EXPORT CastMediaShlib {
 public:
  // Observer for audio loopback data.
  class LoopbackAudioObserver {
   public:
    // Called whenever audio data is about to be output. The |timestamp| is the
    // estimated time in microseconds (relative to CLOCK_MONOTONIC_RAW) that
    // the audio will actually be output. |length| is the length of the audio
    // |data| in bytes. The format of the data is given by |sample_format| and
    // |num_channels|.
    // This method may be called by any thread, and MUST not block or take very
    // much time (to avoid audio underruns).
    virtual void OnLoopbackAudio(int64_t timestamp,
                                 SampleFormat sample_format,
                                 int sample_rate,
                                 int num_channels,
                                 uint8_t* data,
                                 int length) = 0;

    // Called if the loopback data is not continuous (ie, does not accurately
    // represent the actual output) for any reason. For example, if there is an
    // output underflow, or if output is disabled due to no output streams.
    // This method could be called from any thread.
    virtual void OnLoopbackInterrupted() = 0;

    // Called once this observer has been fully removed by a call to
    // RemoveLoopbackAudioObserver(). After this is called, no more calls to
    // OnLoopbackAudio() or OnLoopbackInterrupted() will be made for this
    // observer unless it is added again. This method could be called from any
    // thread.
    virtual void OnRemoved() = 0;

   protected:
    virtual ~LoopbackAudioObserver() {}
  };

  // Initializes platform-specific media systems.  Only called when in an
  // uninitialized state.
  static void Initialize(const std::vector<std::string>& argv);

  // Tears down platform-specific media systems and returns to the uninitialized
  // state.  The implementation must release all media-related hardware
  // resources.
  static void Finalize();

  // Gets the VideoPlane instance for managing the hardware video plane.
  // While an implementation is in an initialized state, this function may be
  // called at any time.  The VideoPlane object must be destroyed in Finalize.
  static VideoPlane* GetVideoPlane();

  // Creates a media pipeline backend.  Called in the browser process for each
  // media pipeline and raw audio stream. The caller owns the returned
  // MediaPipelineBackend instance.
  static MediaPipelineBackend* CreateMediaPipelineBackend(
      const MediaPipelineDeviceParams& params);

  // Fetches the renderer clock rate (Hz).
  static double GetMediaClockRate();

  // Fetches the granularity of clock rate adjustments.
  static double MediaClockRatePrecision();

  // Fetches the possible range of clock rate adjustments.
  static void MediaClockRateRange(double* minimum_rate, double* maximum_rate);

  // Sets the renderer clock rate (Hz).
  static bool SetMediaClockRate(double new_rate);

  // Tests if the implementation supports renderer clock rate adjustments.
  static bool SupportsMediaClockRateChange();

  // Adds a loopback audio observer. An observer will not be added more than
  // once without being removed first.
  // This function is optional to implement.
  static void AddLoopbackAudioObserver(LoopbackAudioObserver* observer)
      __attribute__((__weak__));

  // Removes a loopback audio observer. An observer will not be removed unless
  // it was previously added, and will not be removed more than once without
  // being added again first.
  // Once the observer is fully removed (ie. once it is certain that
  // OnLoopbackAudio() will not be called again for the observer), the
  // observer's OnRemoved() method must be called. The OnRemoved() method must
  // be called once for each time that RemoveLoopbackAudioObserver() is called
  // for a given observer, even if the observer was not added. The
  // implementation may call OnRemoved() from any thread.
  // This function is optional to implement.
  static void RemoveLoopbackAudioObserver(LoopbackAudioObserver* observer)
      __attribute__((__weak__));
};

}  // namespace media
}  // namespace chromecast

#endif  // CHROMECAST_PUBLIC_CAST_MEDIA_SHLIB_H_