Sparkplug is an encoding scheme that uses protobuf for encoding, and is intended as a very full featured, yet efficient data format. Example implementations are here. The Sparkplug encoding can encode data in a number of different formats and even has the capability to encode matrix data. However, it is efficient in that it does not use space in the packet for features that are not used (a feature of protobuf). Protobuf is also nice in that the field names are not included in every packet – they are represented as ints.
Investigating this in the context of the Simple IoT project.