Reland "SelectSettings algorithm for audio constraints."

content/renderer/media/media_stream_constraints_util_audio.h

Index: content/renderer/media/media_stream_constraints_util_audio.h
diff --git a/content/renderer/media/media_stream_constraints_util_audio.h b/content/renderer/media/media_stream_constraints_util_audio.h
new file mode 100644
index 0000000000000000000000000000000000000000..c5e085951fabe86fc3f491db4cb14f0039775884
--- /dev/null
+++ b/content/renderer/media/media_stream_constraints_util_audio.h
@@ -0,0 +1,102 @@
+// 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>
+
+#include "content/common/content_export.h"
+#include "content/common/media/media_devices.mojom.h"
+#include "content/renderer/media/media_stream_constraints_util.h"
+
+namespace blink {
+class WebMediaConstraints;
+}
+
+namespace content {
+
+using AudioDeviceCaptureCapabilities =
+    std::vector<::mojom::AudioInputDeviceCapabilitiesPtr>;
+
+// This function implements the SelectSettings algorithm for audio tracks as
+// described in https://w3c.github.io/mediacapture-main/#dfn-selectsettings
+// The algorithm starts with a set containing all possible candidate settings
+// based on hardware capabilities (passed via the |capabilities| parameter) and
+// supported values for properties not involved in device selection. Candidates
+// that do not support the basic constraint set from |constraints| are removed.
+// If the set of candidates is empty after this step, the function returns an
+// AudioCaptureSettings object without value and whose failed_constraint_name()
+// method returns the name of one of the (possibly many) constraints that could
+// not be satisfied or an empty string if the set of candidates was initially
+// 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.
+//  * 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.
+//  * 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.
+//      - disable_hw_echo_cancellation: For devices that have hardware echo
+//        cancellation, the feature is disabled if the echo_cancellation or
+//        goog_echo_cancellation constraints have a final value of false.
+//      - goog_audio_mirroring: This property is mapped directly from the final
+//        value of the goog_audio_mirroring constraint. If no value is
+//        explicitly specified, the default value is false.
+//    The remaining audio-processing properties are directly mapped from the
+//    final value of the corresponding constraints. If no value is explicitly
+//    specified, the default value is the same as the final value of the
+//    echo_cancellation constraint.  If the echo_cancellation constraint is
+//    not explicitly specified, the default value is implementation defined
+//    (see content::AudioProcessingProperties).
+//    For content capture the rules are the same, but all properties are false
+//    by default, regardless of the value of the echo_cancellation constraint.
+//    Note that it is important to distinguish between audio properties and
+//    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.
+AudioCaptureSettings CONTENT_EXPORT
+SelectSettingsAudioCapture(const AudioDeviceCaptureCapabilities& capabilities,
+                           const blink::WebMediaConstraints& constraints);
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_AUDIO_H_