EXTRA_AUDIO_CONTENTS_URI

Keys into the getExtras Bundle: the audio contents of this notification. This is for use when rendering the notification on an audio-focused interface; the audio contents are a complete sound sample that contains the contents/body of the notification. This may be used in substitute of a Text-to-Speech reading of the notification. For example if the notification represents a voice message this should point to the audio of that message. The data stored under this key should be a String representation of a Uri that contains the audio contents in one of the following formats: WAV, PCM 16-bit, AMR-WB. This extra is unnecessary if you are using MessagingStyle since each Message has a field for holding data URI. That field can be used for audio. See Message#setData. Example usage:

NotificationCompat.Builder myBuilder = (build your Notification as normal);
myBuilder.getExtras().putString(EXTRA_AUDIO_CONTENTS_URI, myAudioUri.toString());