當您嘗試透過 USB API 直接存取 USB 音訊週邊裝置時,可能會發生問題。這些問題可能包括安全性問題、限制其他應用程式的媒體播放,以及透過 USB 裝置播放鬧鐘、通知和鈴聲的遺失情況。
為改善音訊播放品質,請改為設定混音器屬性。
設定混音器屬性
使用 AudioMixerAttributes
API 時,您可以透過 USB 設定應用程式使用偏好的混合器屬性。
當應用程式播放與偏好混音器屬性的編碼格式、頻道遮罩和取樣率相符時,系統會將該播放內容附加至音訊輸出串流,其已設定偏好混合器屬性的混音器屬性。
只要 USB 裝置支援設定,應用程式就能在任何設定下串流至硬體抽象層 (HAL) 和裝置。
AudioMixerAttributes
中允許的兩個混合行為是 DEFAULT
和 BIT_PERFECT
。如果混音器行為為 DEFAULT
,表示混用不同來源的音訊資料。
當混音器行為為 BIT_PERFECT
時,系統不會為播放套用任何音訊混音、音量調整或音訊處理效果。資料會原封不動傳送至 HAL,然後再向下傳送到 USB 裝置。
只要使用 BIT_PERFECT
,即可在 Android 裝置上直接串流數位 (DSD) 訊息,藉此減少脈衝程式碼調節 (PCM)。下列程式碼範例說明如何完成這項操作:
Kotlin
val EXPECTED_FORMAT: AudioFormat = AudioFormat.Builder() .setEncoding(AudioFormat.ENCODING_PCM_24BIT_PACKED) .setChannelMask(AudioFormat.CHANNEL_OUT_STEREO) .setSampleRate(44100) .build() fun startPlayback() { // Query all supported mixer attributes val mixerAttributesList: List<AudioMixerAttributes?> = mAudioManager.getSupportedMixerAttributes(usbDevice) // Find the wanted mixer attributes val mixerAttributes = mixerAttributesList.stream() .filter { mixerAttr: AudioMixerAttributes? -> EXPECTED_FORMAT.equals( mixerAttr!!.format ) } .findAny() .orElse(null) // Register a listener to mixer attributes changed val listener = MyPreferredMixerAttributesChangedListener() mAudioManager.addOnPreferredMixerAttributesChangedListener( Executors.newSingleThreadExecutor(), listener ) // Currently, only media usage over USB devices will be allowed val attr: AudioAttributes = AudioAttributes.Builder() .setUsage(AudioAttributes.USAGE_MEDIA).build() // Set preferred mixer attributes mAudioManager.setPreferredMixerAttributes( attr, usbDevice, mixerAttributes ) // Start playback, note the playback and the audio format must // match what is set when calling `setPreferredMixerAttriutes` // API. val audioTrack = AudioTrack.Builder() .setAudioAttributes(attr) .setAudioFormat(mixerAttributes!!.format) .build() // Clear all preferred mixer attributes related stuff when // playback task is completed mAudioManager.clearPreferredMixerAttributes(attr, usbDevice) mAudioManager.removeOnPreferredMixerAttributesChangedListener(listener) } private class MyPreferredMixerAttributesChangedListener : AudioManager.OnPreferredMixerAttributesChangedListener { override fun onPreferredMixerAttributesChanged( attributes: AudioAttributes, device: AudioDeviceInfo, mixerAttributes: AudioMixerAttributes?, ) { // Do something when preferred mixer attributes changed } }
Java
final AudioFormat EXPECTED_FORMAT = new AudioFormat.Builder() .setEncoding(AudioFormat.ENCODING_PCM_24BIT_PACKED) .setChannelMask(AudioFormat.CHANNEL_OUT_STEREO) .setSampleRate(44100) .build(); void startPlayback() { // Query all supported mixer attributes List<AudioMixerAttributes> mixerAttributesList = mAudioManager.getSupportedMixerAttributes(usbDevice); // Find the wanted mixer attributes AudioMixerAttributes mixerAttributes = mixerAttributesList.stream() .filter(mixerAttr -> EXPECTED_FORMAT.equals(mixerAttr.getFormat())) .findAny() .orElse(null); // Register a listener to mixer attributes changed MyPreferredMixerAttributesChangedListener listener = new MyPreferredMixerAttributesChangedListener(); mAudioManager.addOnPreferredMixerAttributesChangedListener( Executors.newSingleThreadExecutor(), listener); // Currently, only media usage over USB devices will be allowed AudioAttributes attr = new AudioAttributes.Builder() .setUsage(AudioAttributes.USAGE_MEDIA).build(); // Set preferred mixer attributes mAudioManager.setPreferredMixerAttributes( attr, usbDevice, mixerAttributes); // Start playback, note the playback and the audio format must // match what is set when calling `setPreferredMixerAttriutes` // API. AudioTrack audioTrack = new AudioTrack.Builder() .setAudioAttributes(attr) .setAudioFormat(mixerAttributes.getFormat()) .build(); // Clear all preferred mixer attributes related stuff when // playback task is completed mAudioManager.clearPreferredMixerAttributes(attr, usbDevice); mAudioManager.removeOnPreferredMixerAttributesChangedListener( listener); } private class MyPreferredMixerAttributesChangedListener implements AudioManager.OnPreferredMixerAttributesChangedListener { @Override public void onPreferredMixerAttributesChanged( AudioAttributes attributes, AudioDeviceInfo device, AudioMixerAttributes mixerAttributes) { // Do something when preferred mixer attributes changed } }