An .rx2 is a Propellerhead ReCycle loop: an IFF-style CAT group whose form type is REX2, holding big-endian chunks. ReCycle slices a drum or instrument loop into transient-aligned segments and stores the slice markers so a host can retrigger each and follow tempo. The markers hide in a nested CAT/SLCL group. The format was never openly published: for years the only way to read a REX2 was Propellerhead's NDA-licensed REX Shared Library SDK, so it is reverse-engineered. Hover any field or byte to light its span and read the decode. Color marks kind (see the key).
An IFF CAT group, form type REX2, of big-endian chunks. The slice markers hide in a nested sub-group.
The group header, drawn above: the CAT keyword, the group size, and the REX2 form type. IFF reserves CAT for concatenating FORM/LIST groups, with the word after its size a hint at their type; REX2 repurposes that slot for a real form id (REX2) and hangs the chunks straight off the CAT, using it where IFF would use a FORM.
Big-endian IFF, from a real ReCycle loop. Note the form type between the two.
Big-endian IFF chunks: a 4-byte id, a 4-byte size, then the body (padded to even). The legible strings decode as text; the remaining bodies are opaque payload.
The transient slice markers do not sit at the top level: they live in a nested CAT group whose form is SLCL, one SLCE per slice. A reader must recurse into it to count slices; a flat top-level walk misses them.