MediaStream.getAudioTracks() - Web APIs
early versions of this api included a special audiostreamtrack interface which was used as the type for each entry in the list of audio streams; however, this has since been merged into the main mediastreamtrack interface.

Media Capture and Streams API (Media Stream) - Web APIs
blobevent canvascapturemediastreamtrack inputdeviceinfo mediadevicekind mediadeviceinfo mediadevices mediastream mediastreamconstraints mediastreamevent mediastreamtrack mediastreamtrackevent mediatrackconstraints mediatracksettings mediatracksupportedconstraints overconstrainederror url early versions of the media capture and streams api specification included separate audiostreamtrack and videostreamtrack interfaces—each based upon mediastreamtrack—which represented streams of those types.