You're describing the type-length-value format, used in some places in digital video or in Open Sound Control. Basically you have a TYPE (fixed width, eg. 16 b

You're describing the type-length-value format, used in some places in digital video or in Open Sound Control. Basically you have a TYPE (fixed width, eg. 16 bits), a LENGTH (again fixed) and a VALUE which is simply a stream of bytes that goes on for LENGTH bytes and is interpreted based on what TYPE it is. You can nest your fields and get very creative in quite a compact way. One could represent a JSON document with TLV by adding an associative map between the field names and their type numbers, then stream away. I always loved the simplicity of TLV. Though nowadays, I'm not sure this has much of an advantage over gzipped JSON.