Dolphin Introduces RVZ as a Lossless, Emulation-Ready Disc Format

On July 5, 2020, the Dolphin project detailed support for WIA and its new RVZ format in development build 5.0-12188. RVZ was designed to compress GameCube and Wii images efficiently while retaining the ability to reconstruct verifiable disc data and maintain real-time emulator performance.

The problem with “unused” disc data

GameCube and Wii optical images contain more than obvious filesystem files. They include partition structure, encrypted Wii data, update content, alignment, and large regions that can look like random padding. Generic compression performs poorly on high-entropy bytes, while older space-saving formats often removed or normalized areas presumed irrelevant to gameplay.

That can be convenient and still unsuitable for a preservation master. Data considered unused today may matter for a full-disc hash, forensic comparison, unusual software behavior, future research, or reconstruction of the original layout. Once discarded, it cannot be recovered from the derivative merely because every familiar game scene still boots.

Dolphin’s report explains that GameCube and Wii “junk” is generated predictably. A format can describe those regions compactly and regenerate them during decompression rather than storing every pseudorandom-looking byte. It can also compress data in chunks designed for random access so the emulator does not need to expand an entire disc before play.

WIA, RVZ, and real-time access

WIA supplied a flexible Wii/GameCube archive design, but Dolphin found parts of its compression behavior too expensive for smooth on-demand emulation. RVZ revised the layout and compression choices for faster random reads and practical real-time use. The development build could convert images through Dolphin’s graphical interface and DolphinTool.

RVZ supports compression methods and configurable compression levels. Higher settings can reduce storage while taking longer to create and potentially more work to read. The useful setting depends on CPU, storage, archive scale, and whether the file is an active-play derivative or a preservation object. Format support does not guarantee every third-party tool implements every option correctly.

“RVZ” alone does not prove losslessness

The project contrasted RVZ with formats that scrub or omit unused-looking content. Wii update partitions, encrypted data, and apparently meaningless padding can matter to preservation, future verification, determinism, or obscure game behavior. RVZ reorganizes data for compression without making the archival master irrecoverable when used losslessly.

Dolphin’s conversion tools also expose options such as removing junk data. Selecting a destructive option makes the result lossy even when the filename ends in .rvz. Preservation records must retain the exact conversion settings, Dolphin build, source and output hashes, and verification result. An extension identifies a container family, not the quality or provenance of its contents.

The safe acceptance test is a round trip. Start with a verified canonical image, convert it to RVZ using reviewed lossless settings, convert it back to the canonical image representation, and compare the expected cryptographic hashes. For Wii images, use Dolphin’s verification features and preserve partition information and keys lawfully required by the workflow. Test more than whether a game launches.

Compatibility is part of format stewardship

Compatibility was a real boundary: older Dolphin builds could not read RVZ. The release therefore illustrates a broader preservation rule—record the tool and format version, retain verification hashes, and keep a documented path back to a canonical image.

An archive should preserve format documentation and open decoder source in addition to files. Keep a known-good Dolphin or DolphinTool build and test restoration periodically on supported host platforms. If the archive retains only RVZ, its recovery plan depends on a future decoder; retaining the verified canonical source as a separate master removes that single-format dependency at the cost of storage.

For active collections, RVZ can be a useful lossless master or derivative when the organization has validated round trips and tools. Some archives may instead keep raw canonical images immutable and generate RVZ access copies. Both approaches are defensible when documented; silently replacing a source and deleting the evidence is not.

Why the 2020 release mattered

RVZ aligned two goals often treated as opposites: strong compression and retention of the defined disc image. It showed that “emulation-ready” does not have to mean scrubbing data, while still acknowledging that user-selected conversion settings can cross into lossy territory.

The format is not a substitute for acquisition. A perfect RVZ conversion of a bad, incomplete, or incorrectly dumped disc preserves the bad input exactly. Verify source provenance, use current platform-specific dumping guidance, preserve logs and metadata, and then validate the container transformation.

A durable record includes physical disc identifier, region and revision, acquisition hardware and software, canonical hashes, RVZ format/tool version, compression method and level, destructive-option status, output hash, round-trip result, and storage fixity history. Those facts make “lossless” independently auditable rather than a claim inferred from a filename. Related: The History of Emulation: Preserving Gaming’s Hardware Before It’s Gone · Preservation-Grade Game Images: Dumps, Hashes, DATs, and Disc Formats Explained

Sources: Dolphin Progress Report: May and June 2020, Dolphin disc-conversion guide, DolphinTool source, WIA/RVZ implementation