关于audio_policy_configuration.xml文件的说明

<!-- Modules section:
        There is one section per audio HW module present on the platform.
        Each module section will contains two mandatory tags for audio HAL “halVersion” and “name”.
        The module names are the same as in current .conf file:
                “primary”, “A2DP”, “remote_submix”, “USB”
        Each module will contain the following sections:
        “devicePorts”: a list of device descriptors for all input and output devices accessible via this
        module.
        This contains both permanently attached devices and removable devices.
        “mixPorts”: listing all output and input streams exposed by the audio HAL
        “routes”: list of possible connections between input and output devices or between stream and devices.
            "route": is defined by an attribute:
                -"type": <mux|mix> means all sources are mutual exclusive (mux) or can be mixed (mix)
                -"sink": the sink involved in this route
                -"sources": all the sources than can be connected to the sink via vis route
        “attachedDevices”: permanently attached devices.
        The attachedDevices section is a list of devices names. The names correspond to device names
        defined in <devicePorts> section.
        “defaultOutputDevice”: device to be used by default when no policy rule applies
    -->

举个例子

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!-- Copyright (C) 2017 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
-->

<audioPolicyConfiguration version="1.0" xmlns:xi="http://www.w3.org/2001/XInclude">
    <globalConfiguration speaker_drc_enabled="true"/>

    <modules>
        <module name="primary" halVersion="2.0">
            <attachedDevices>
                <item>Speaker</item>
                <item>Wired Headphone</item>
                <item>Built-In Mic</item>
            </attachedDevices>
            <defaultOutputDevice>Speaker</defaultOutputDevice>
            <mixPorts>
                <mixPort name="primary output" role="source" flags="AUDIO_OUTPUT_FLAG_PRIMARY">
                    <profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
                             samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
                </mixPort>
                <mixPort name="headphone output" role="source" flags="AUDIO_OUTPUT_FLAG_DIRECT|AUDIO_OUTPUT_FLAG_HW_AV_SYNC">
                    <profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
                             samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
                </mixPort>

                <mixPort name="primary input" role="sink">
                    <profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
                             samplingRates="8000,11025,16000,22050,24000,32000,44100,48000"
                             channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO"/>
                </mixPort>
            </mixPorts>
            <devicePorts>
                <devicePort tagName="Speaker" type="AUDIO_DEVICE_OUT_SPEAKER" role="sink" >
                </devicePort>
                <devicePort tagName="Wired Headphone" type="AUDIO_DEVICE_OUT_WIRED_HEADPHONE" role="sink">
                </devicePort>

                <devicePort tagName="Built-In Mic" type="AUDIO_DEVICE_IN_BUILTIN_MIC" role="source">
                </devicePort>
                <devicePort tagName="Spdif-In" type="AUDIO_DEVICE_IN_AUX_DIGITAL" role="source">
                </devicePort>
            </devicePorts>
            <routes>
                <route type="mix" sink="Speaker"
                       sources="primary output"/>
                <route type="mix" sink="Wired Headphone"
                       sources="primary output,headphone output"/>

                <route type="mix" sink="primary input"
                       sources="Built-In Mic,Spdif-In"/>
            </routes>
        </module>

        <!-- A2dp Audio HAL -->
        <xi:include href="a2dp_audio_policy_configuration.xml"/>
        <!-- Usb Audio HAL -->
        <xi:include href="usb_audio_policy_configuration.xml"/>
        <!-- Remote Submix Audio HAL -->
        <xi:include href="r_submix_audio_policy_configuration.xml"/>
    </modules>
    <!-- Volume section -->
    <xi:include href="audio_policy_volumes.xml"/>
    <xi:include href="default_volume_tables.xml"/>
</audioPolicyConfiguration>

route是由mixPort和devicePort构成，mixPort一般作为source，而devicePort一般作为sink。