The activeSourceBuffers read-only property of the MediaSource interface returns a SourceBufferList object containing a subset of the SourceBuffer objects contained within SourceBuffers — the list of objects providing the selected video track, enabled audio tracks, and shown/hidden text tracks.
The MediaTrackSettings dictionary is used to return the current values configured for each of a MediaStreamTrack's settings. These values will adhere as closely as possible to any constraints previously set using applyConstraints(), and will adhere to the default constraints for any properties whose constraints haven't been changed, or whose customized constraints couldn't be matched.
The MediaKeySystemConfiguration.initDataTypes read-only property returns a list of supported initialization data type names. An initialization data type is a string indicating the format of the initialization data.