Abstract: This paper presents a new method of encoding performance data in MEI using the recently added <extData> element. Performance data was extracted using the Automatic Music Performance Analysis and Comparison Toolkit (AMPACT) and encoded as a JSON object within an <extData> element linked to a specific musical note. A set of pop music vocals has been encoded to demonstrate both the range of descriptors that can be encoded in <extData> and how this method can be used for transcriptions in the absence of a fully specified musical score.