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+If MediaKeys is set before playback starts, the implementation **MUST** support switching between clear and encrypted streams.
+
+_NOTE_: Whether the clear and encrypted streams - or even multiple streams of either type - may use different contentTypes is left to other specifications related to media sources and capability detection.
+
+_NOTE_: Applications are advised that at the time of this writing, at least some major browser do not support this.
+
+Support of switching when MediaKeys is set after the playback starts, or when the clear stream uses a different contentType, is a quality of implementation issue.
+
+_NOTE_: Applications are advised that at the time of this writing, at least some major browser do not support this. Applications that need this functionality **SHOULD** set MediaKeys before loading the media resource.
+