Vemos AudioPolicyManager::onNewAudioModulesAvailableInt(DeviceVector *newDevices)en la función que crea SwAudioOutputDescriptorel objeto, cuyo constructor se define frameworks/av/services/audiopolicy/common/managerdefinitions/src/AudioOutputDescriptor.cppde la siguiente manera:
AudioOutputDescriptor::AudioOutputDescriptor(const sp<PolicyAudioPort>& policyAudioPort,
AudioPolicyClientInterface *clientInterface)
: mPolicyAudioPort(policyAudioPort), mClientInterface(clientInterface)
{
if (mPolicyAudioPort.get() != nullptr) {
mPolicyAudioPort->pickAudioProfile(mSamplingRate, mChannelMask, mFormat);
if (mPolicyAudioPort->asAudioPort()->getGains().size() > 0) {
mPolicyAudioPort->asAudioPort()->getGains()[0]->getDefaultConfig(&mGain);
}
}
}
. . . . . .
SwAudioOutputDescriptor::SwAudioOutputDescriptor(const sp<IOProfile>& profile,
AudioPolicyClientInterface *clientInterface)
: AudioOutputDescriptor(profile, clientInterface),
mProfile(profile), mIoHandle(AUDIO_IO_HANDLE_NONE), mLatency(0),
mFlags((audio_output_flags_t)0),
mOutput1(0), mOutput2(0), mDirectOpenCount(0),
mDirectClientSession(AUDIO_SESSION_NONE)
{
if (profile != NULL) {
mFlags = (audio_output_flags_t)profile->getFlags();
}
}
Para abrir una secuencia de salida de audio en Android, los principales parámetros necesarios son la frecuencia de muestreo, la máscara de canal (número de canales), el formato de muestreo, la ganancia y las banderas IOProfile. Como se explica en el artículo sobre carga de información del dispositivo de audio Android , IOProfilela información proviene principalmente del análisis audio_policy_configuration.xmldel archivo de configuración de la política de audio, más específicamente, del elemento mixPort en el archivo de configuración de la política de audio, como device/generic/car/emulator/audio/audio_policy_configuration.xmlse muestra a continuación (ubicado):
<defaultOutputDevice>bus0_media_out</defaultOutputDevice>
<mixPorts>
<mixPort name="mixport_bus0_media_out" 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="mixport_bus200_audio_zone_2" role="source">
<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="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</mixPort>
IOProfileEstablecer una conexión AudioRoutecon DeviceDescriptor. En el archivo de configuración de la política de audio, los elementos XML AudioRoutecorrespondientes DeviceDescriptorse definen de la siguiente manera:
<devicePorts>
<devicePort tagName="bus0_media_out" role="sink" type="AUDIO_DEVICE_OUT_BUS"
address="bus0_media_out">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
<gains>
<gain name="" mode="AUDIO_GAIN_MODE_JOINT"
minValueMB="-3200" maxValueMB="600" defaultValueMB="0" stepValueMB="100"/>
</gains>
</devicePort>
. . . . . .
<routes>
<route type="mix" sink="bus0_media_out" sources="mixport_bus0_media_out"/>
SwAudioOutputDescriptorLas banderas y ganancias provienen directamente del elemento mixPort del archivo de configuración de la política de audio. El archivo de configuración de política de audio admite la definición de ganancia para mixPort y devicePort . El archivo de configuración anterior no define la ganancia para mixPort . La frecuencia de muestreo, la máscara de canal (número de canales) y el formato de muestreo seleccionarán AudioProfileel mejor entre múltiples. La estrategia específica es la siguiente: PolicyAudioPort::pickAudioProfile()La definición de la función (ubicada frameworks/av/services/audiopolicy/common/managerdefinitions/src/PolicyAudioPort.cpp):
void PolicyAudioPort::pickSamplingRate(uint32_t &pickedRate,
const SampleRateSet &samplingRates) const
{
pickedRate = 0;
// For direct outputs, pick minimum sampling rate: this helps ensuring that the
// channel count / sampling rate combination chosen will be supported by the connected
// sink
if (isDirectOutput()) {
uint32_t samplingRate = UINT_MAX;
for (const auto rate : samplingRates) {
if ((rate < samplingRate) && (rate > 0)) {
samplingRate = rate;
}
}
pickedRate = (samplingRate == UINT_MAX) ? 0 : samplingRate;
} else {
uint32_t maxRate = SAMPLE_RATE_HZ_MAX;
// For mixed output and inputs, use max mixer sampling rates. Do not
// limit sampling rate otherwise
// For inputs, also see checkCompatibleSamplingRate().
if (asAudioPort()->getType() == AUDIO_PORT_TYPE_MIX) {
maxRate = UINT_MAX;
}
// TODO: should mSamplingRates[] be ordered in terms of our preference
// and we return the first (and hence most preferred) match? This is of concern if
// we want to choose 96kHz over 192kHz for USB driver stability or resource constraints.
for (const auto rate : samplingRates) {
if ((rate > pickedRate) && (rate <= maxRate)) {
pickedRate = rate;
}
}
}
}
void PolicyAudioPort::pickChannelMask(audio_channel_mask_t &pickedChannelMask,
const ChannelMaskSet &channelMasks) const
{
pickedChannelMask = AUDIO_CHANNEL_NONE;
// For direct outputs, pick minimum channel count: this helps ensuring that the
// channel count / sampling rate combination chosen will be supported by the connected
// sink
if (isDirectOutput()) {
uint32_t channelCount = UINT_MAX;
for (const auto channelMask : channelMasks) {
uint32_t cnlCount;
if (asAudioPort()->useInputChannelMask()) {
cnlCount = audio_channel_count_from_in_mask(channelMask);
} else {
cnlCount = audio_channel_count_from_out_mask(channelMask);
}
if ((cnlCount < channelCount) && (cnlCount > 0)) {
pickedChannelMask = channelMask;
channelCount = cnlCount;
}
}
} else {
uint32_t channelCount = 0;
uint32_t maxCount = MAX_MIXER_CHANNEL_COUNT;
// For mixed output and inputs, use max mixer channel count. Do not
// limit channel count otherwise
if (asAudioPort()->getType() != AUDIO_PORT_TYPE_MIX) {
maxCount = UINT_MAX;
}
for (const auto channelMask : channelMasks) {
uint32_t cnlCount;
if (asAudioPort()->useInputChannelMask()) {
cnlCount = audio_channel_count_from_in_mask(channelMask);
} else {
cnlCount = audio_channel_count_from_out_mask(channelMask);
}
if ((cnlCount > channelCount) && (cnlCount <= maxCount)) {
pickedChannelMask = channelMask;
channelCount = cnlCount;
}
}
}
}
/* format in order of increasing preference */
const audio_format_t PolicyAudioPort::sPcmFormatCompareTable[] = {
AUDIO_FORMAT_DEFAULT,
AUDIO_FORMAT_PCM_16_BIT,
AUDIO_FORMAT_PCM_8_24_BIT,
AUDIO_FORMAT_PCM_24_BIT_PACKED,
AUDIO_FORMAT_PCM_32_BIT,
AUDIO_FORMAT_PCM_FLOAT,
};
int PolicyAudioPort::compareFormats(audio_format_t format1, audio_format_t format2)
{
// NOTE: AUDIO_FORMAT_INVALID is also considered not PCM and will be compared equal to any
// compressed format and better than any PCM format. This is by design of pickFormat()
if (!audio_is_linear_pcm(format1)) {
if (!audio_is_linear_pcm(format2)) {
return 0;
}
return 1;
}
if (!audio_is_linear_pcm(format2)) {
return -1;
}
int index1 = -1, index2 = -1;
for (size_t i = 0;
(i < ARRAY_SIZE(sPcmFormatCompareTable)) && ((index1 == -1) || (index2 == -1));
i ++) {
if (sPcmFormatCompareTable[i] == format1) {
index1 = i;
}
if (sPcmFormatCompareTable[i] == format2) {
index2 = i;
}
}
// format1 not found => index1 < 0 => format2 > format1
// format2 not found => index2 < 0 => format2 < format1
return index1 - index2;
}
uint32_t PolicyAudioPort::formatDistance(audio_format_t format1, audio_format_t format2)
{
if (format1 == format2) {
return 0;
}
if (format1 == AUDIO_FORMAT_INVALID || format2 == AUDIO_FORMAT_INVALID) {
return kFormatDistanceMax;
}
int diffBytes = (int)audio_bytes_per_sample(format1) -
audio_bytes_per_sample(format2);
return abs(diffBytes);
}
bool PolicyAudioPort::isBetterFormatMatch(audio_format_t newFormat,
audio_format_t currentFormat,
audio_format_t targetFormat)
{
return formatDistance(newFormat, targetFormat) < formatDistance(currentFormat, targetFormat);
}
void PolicyAudioPort::pickAudioProfile(uint32_t &samplingRate,
audio_channel_mask_t &channelMask,
audio_format_t &format) const
{
format = AUDIO_FORMAT_DEFAULT;
samplingRate = 0;
channelMask = AUDIO_CHANNEL_NONE;
// special case for uninitialized dynamic profile
if (!asAudioPort()->hasValidAudioProfile()) {
return;
}
audio_format_t bestFormat = sPcmFormatCompareTable[ARRAY_SIZE(sPcmFormatCompareTable) - 1];
// For mixed output and inputs, use best mixer output format.
// Do not limit format otherwise
if ((asAudioPort()->getType() != AUDIO_PORT_TYPE_MIX) || isDirectOutput()) {
bestFormat = AUDIO_FORMAT_INVALID;
}
const AudioProfileVector& audioProfiles = asAudioPort()->getAudioProfiles();
for (size_t i = 0; i < audioProfiles.size(); i ++) {
if (!audioProfiles[i]->isValid()) {
continue;
}
audio_format_t formatToCompare = audioProfiles[i]->getFormat();
if ((compareFormats(formatToCompare, format) > 0) &&
(compareFormats(formatToCompare, bestFormat) <= 0)) {
uint32_t pickedSamplingRate = 0;
audio_channel_mask_t pickedChannelMask = AUDIO_CHANNEL_NONE;
pickChannelMask(pickedChannelMask, audioProfiles[i]->getChannels());
pickSamplingRate(pickedSamplingRate, audioProfiles[i]->getSampleRates());
if (formatToCompare != AUDIO_FORMAT_DEFAULT && pickedChannelMask != AUDIO_CHANNEL_NONE
&& pickedSamplingRate != 0) {
format = formatToCompare;
channelMask = pickedChannelMask;
samplingRate = pickedSamplingRate;
// TODO: shall we return on the first one or still trying to pick a better Profile?
}
}
}
ALOGV("%s Port[nm:%s] profile rate=%d, format=%d, channels=%d", __FUNCTION__,
asAudioPort()->getName().c_str(), samplingRate, channelMask, format);
}
Para el formato de muestreo, cuanto mayor sea la precisión, mayor será la prioridad; para la máscara de canal (número de canales), si es salida directa (Direct Output), cuanto menor sea el número de canales, mayor será la prioridad; en caso contrario, el cuanto mayor sea el número de canales, mayor será la prioridad. ; Para la frecuencia de muestreo, si es salida directa (salida directa), cuanto menor sea la frecuencia de muestreo, mayor será la prioridad. De lo contrario, cuanto mayor sea la frecuencia de muestreo, mayor será la prioridad. .