Remove support for some device constraints from SelectSettings.

content/renderer/media/media_stream_constraints_util_audio.h

 // Copyright 2017 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 CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_AUDIO_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_AUDIO_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 23 matching lines @@
 // empty (e.g., if there are no devices in the system).
 // After the basic constraint set is applied, advanced constraint sets are
 // applied. If no candidates can satisfy an advanced set, the advanced set is
 // ignored, otherwise the candidates that cannot satisfy the advanced set are
 // removed.
 // Once all constraint sets are applied, the result is selected from the
 // remaining candidates by giving preference to candidates closest to the ideal
 // values specified in the basic constraint set, or using default
 // implementation-specific values.
 // The result includes the following properties:
-//  * Device. A device is chosen using the device_id, sample_rate, sample_size,
-//    and channel_count constraints. If multiple devices satisfy the constraints
-//    preference is given to the default device (system defined or chosen by
-//    user preferences). If the default device is not included in the valid
-//    candidates, the first valid device in the list obtained by querying the
-//    system capabilities is chosen. For content capture, no real audio input
-//    devices are used and the sample_rate, sample_size and channel_count
-//    constraints are ignored. In content capture, the deviceId constraint is
-//    supported and is interpreted by the system as a string that indicates,
-//    for example, which tab to capture. Validation for that "device" ID is
-//    performed by the getUserMedia implementation. To decide between content
-//    or device capture, the value of the special media_stream_source constraint
-//    is used.
+//  * Device. A device can be chosen using the device_id constraint.
+//    For device capture, the validity of device IDs is checked by
+//    SelectSettings since the list of allowed device IDs is known in advance.
+//    For content capture, all device IDs are considered valid by
+//    SelectSettings. Actual validation is performed by the getUserMedia
+//    implementation.
 //  * Audio features: the hotword_enabled, disable_local_echo and
 //    render_to_associated_sink constraints can be used to enable the
 //    corresponding audio feature. If not specified, their default value is
-//    false.
+//    false, except for disable_local_echo, whose default value is false only
+//    for desktop capture.
 //  * Audio processing. The remaining constraints are used to control audio
 //    processing. This is how audio-processing properties are set for device
 //    capture(see the content::AudioProcessingProperties struct) :
 //      - enable_sw_echo_cancellation: If the selected device has hardware echo
 //        cancellation, software echo cancellation is disabled regardless of
 //        any constraint values. Otherwise, it is enabled by default unless
 //        either the echo_cancellation or the goog_echo_cancellation constraint
 //        has a final value of false after applying all constraint sets. Note
 //        that if these constraints have contradictory values, SelectSettings
 //        fails and returns no value.
@@ skipping 15 matching lines @@
 //    constraints. Constraints are an input to SelectSettings, while properties
 //    are part of the output. The value for most boolean properties comes
 //    directly from a corresponding boolean constraint, but this is not true for
 //    all constraints and properties. For example, the echo_cancellation and
 //    goog_echo_cancellation constraints  are not directly mapped to any
 //    property, but they, together with hardware characteristics, influence the
 //    enabling and disabling of software and hardware echo cancellation.
 //    Moreover, the echo_cancellation constraint influences most other
 //    audio-processing properties for which no explicit value is provided in
 //    their corresponding constraints.
+// TODO(guidou): Add support for other standard constraints such as sampleRate,
+// channelCount and groupId. http://crbug.com/731170
 AudioCaptureSettings CONTENT_EXPORT
 SelectSettingsAudioCapture(const AudioDeviceCaptureCapabilities& capabilities,
                            const blink::WebMediaConstraints& constraints);
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_AUDIO_H_