Add an initial revision of an audio server.

mojo/services/media/audio/interfaces/audio_track.mojom

Index: mojo/services/media/audio/interfaces/audio_track.mojom
diff --git a/mojo/services/media/audio/interfaces/audio_track.mojom b/mojo/services/media/audio/interfaces/audio_track.mojom
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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.
+
+module mojo.media;
+
+import "mojo/services/media/common/interfaces/media_common.mojom";
+import "mojo/services/media/common/interfaces/media_pipe.mojom";
+import "mojo/services/media/common/interfaces/media_types.mojom";
+import "mojo/services/media/common/interfaces/rate_control.mojom";
+
+struct AudioTrackDescriptor {
+  // The track supports the union of all these media type sets.
+  array<MediaTypeSet> supported_media_types;
+};
+
+struct AudioTrackConfiguration {
+  // The media type to use.
+  MediaType media_type;
+
+  // Desired maximum buffer size, in frames of audio.
+  uint64 max_frames;
+
+  // Ratio of audio frames to media time ticks.
+  // 
+  // Presentation time stamps on audio packets are expressed in units of media
+  // time ticks.  Many users will choose to use units of audio frames to express
+  // their media time, and can simply leave this ratio at the default of 1:1.
+  // For some, however, it may be more convenient to use different units for
+  // media time.  For example, if the audio frame rate was 48KHz, and the time
+  // stamps are expressed in 90KHz units (the units used by MPEG-2 Program
+  // Stream timestamps), the ratio should be set to 48000:90000 (aka, 8:15).
+  // IOW - audio_frame_ratio would be set to 8 and media_time_ratio would be set
+  // to 15.
+  //
+  // Neither of these values may be 0.  A configuration error will occur if they
+  // are.
+  uint32 audio_frame_ratio = 1;
+  uint32 media_time_ratio  = 1;
+};
+
+interface AudioTrack {
+  // Get the descriptor.
+  Describe() => (AudioTrackDescriptor descriptor);
+
+  // Set the configuration, receive a pipe to send data to in return.
+  // Possible results include...
+  //
+  // kOK:
+  //   Configuration successful, the bound pipe interface is ready to be used.
+  // 
+  // kInvalidArgs:
+  //   One or more of the configuration arguments are illegal.  For example, a
+  //   value of 0 for either numerator or denominator of the audio frame to
+  //   media time ratio.
+  //
+  // kUnsupportedConfig:
+  //   The requested configuration is not supported by this track.
+  //
+  // kInsufficientResources:
+  //   Resource limitations prevent configuring the audio track is the desired
+  //   way.  Perhaps there is not enough RAM to support the 2.7 days of audio
+  //   buffer you requested, or perhaps there is not enough CPU power given the
+  //   existing active tracks in the system to support rendering 128 channels
+  //   at 1.5 MHz frame rate.
+  //
+  // kBadState:
+  //  The track is already configured and has pending data in its pipe.  Data
+  //  needs to be flushed and the media clock must be stopped before the track
+  //  may be re-configured.
+  Configure(AudioTrackConfiguration configuration,
+            MediaPipe& pipe) => (MediaResult result);
+
+  // Request the rate control interface for this AudioTrack
+  // Possbile results include...
+  //
+  // kOK:
+  //  Everything went well.
+  //
+  // kBadState:
+  //  Rate control interface is already bound to a different client.
+  GetRateControl(RateControl& rate_control) => (MediaResult result);
+};