Implementation of 'AudioContext.getOutputTimestamp' method

media/audio/alsa/alsa_output.h

 // Copyright 2013 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.
 //
 // Creates an output stream based on the ALSA PCM interface.
 //
 // On device write failure, the stream will move itself to an invalid state.
 // No more data will be pulled from the data source, or written to the device.
 // All calls to public API functions will either no-op themselves, or return an
 // error if possible.  Specifically, If the stream is in an error state, Open()
@@ skipping 188 matching lines @@
 
   // Handle to the actual PCM playback device.
   snd_pcm_t* playback_handle_;
 
   std::unique_ptr<media::SeekableBuffer> buffer_;
   uint32_t frames_per_packet_;
 
   InternalState state_;
   float volume_;  // Volume level from 0.0 to 1.0.
 
+  // Total amount of the frames written from the playback start.
+  snd_pcm_sframes_t elapsed_written_frames_;
+
   AudioSourceCallback* source_callback_;
 
   // Container for retrieving data from AudioSourceCallback::OnMoreData().
   std::unique_ptr<AudioBus> audio_bus_;
 
   // Channel mixer and temporary bus for the final mixed channel data.
   std::unique_ptr<ChannelMixer> channel_mixer_;
   std::unique_ptr<AudioBus> mixed_audio_bus_;
 
   // Allows us to run tasks on the AlsaPcmOutputStream instance which are
   // bound by its lifetime.
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<AlsaPcmOutputStream> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AlsaPcmOutputStream);
 };
 
 MEDIA_EXPORT std::ostream& operator<<(std::ostream& os,
                                       AlsaPcmOutputStream::InternalState);
 
 };  // namespace media
 
 #endif  // MEDIA_AUDIO_ALSA_ALSA_OUTPUT_H_