Valve Tests Pyrowave, an Open-Source GPU Streaming Codec

Valve added an experimental video codec called Pyrowave to the Steam Client Beta on Sept. 21, giving Steam Remote Play a way to trade network bandwidth for latency low enough to keep pace with a wired connection.

Valve announced the feature in Steam Client Beta patch notes posted to its Steam Community forum, writing that Pyrowave "allows high bandwidth, low latency video streaming" and pointing users to a companion post in the Steam Remote Play discussion group for details. That companion post names the codec's creator: Hans-Kristian Arntzen, the graphics programmer behind the VKD3D-Proton translation layer that lets Direct3D 12 games run on Vulkan.

How Pyrowave differs from H.264 and H.265

Arntzen has published Pyrowave's source under the MIT license at github.com/Themaister/pyrowave. The repository describes it as an intra-only codec, meaning every frame is encoded independently rather than referencing the ones before it, built entirely in Vulkan compute shaders. Instead of the block-based compression that H.264, H.265 and AV1 use, Pyrowave runs a discrete wavelet transform with CDF 9/7 filters, the same mathematical family JPEG2000 uses for still images. The README states encode and decode together take under 0.1 millisecond at 1080p and under 0.2 millisecond at 4K on suitable GPU hardware, with a target bitrate above 200 Mbit/s.

The bandwidth-for-latency trade

In the Remote Play discussion post, Valve says Pyrowave uses five to ten times the bandwidth of the codecs Steam already supports, so it recommends both machines connect to the same router over at least Gigabit Ethernet rather than Wi-Fi. Streamers can let Steam tune bitrate automatically or set a fixed rate between 100 Mbit/s and 500 Mbit/s. The codec also supports YUV 4:4:4 color, useful for reading desktop text on a 4K display, and HDR, which Valve turns on automatically when both the host and the client support it. Pyrowave is off by default and has to be switched on in Remote Play's advanced client settings.

What shipped Sept. 21 and what changed a day later

Pyrowave reached Steam Beta on Windows and macOS immediately. On Linux, it requires opting into the experimental SteamRT3 Steam Client in System Settings; Valve says the codec is coming to the Steam Link mobile app later without giving a date. A follow-up beta the next day, according to the same patch notes feed, added a -pyrowavestats command-line flag for logging encoding performance, fixed a GPU memory leak triggered by frequently changing resolutions, fixed occasional flickering when streaming to Linux and SteamOS clients, and moved encoding onto the GPU's compute queue so it stops competing with the game itself for graphics time.

Client	Status as of Sept. 22 beta
Windows / macOS	Live in Steam Beta, off by default
Linux / SteamOS	Live, requires the SteamRT3 experimental client
Steam Link app	Not yet; Valve says it is coming

GamingOnLinux confirmed the same enablement path and bitrate range independently after testing the beta, and said the desktop toggle sits under Settings, Interface, while Steam Deck exposes it under System settings instead.

Valve has not said when Pyrowave will leave beta or become the default codec for any device, and the discussion post frames it as something to try rather than a replacement: "your particular setup may or may not benefit from the new codec." Arntzen's repository carries its own disclaimer that the project is under active development, with the bitstream format still subject to change before a stable release. Steam's own open-source push this month has run in parallel with other infrastructure projects going public, including Dreamnum's Univer office SDK, which reached its 1.0 release with an MIT-style license of its own in September.

What to watch next

The open license means Pyrowave is already showing up outside Valve's own client: its GitHub README lists Sunshine and Moonlight, two existing open-source game-streaming projects, as likely adopters, the same pattern that let Vectorize's Hindsight memory format spread once its code went public. Whether Pyrowave becomes a Steam Link default depends on hardware Valve has not detailed publicly: encoding on the compute queue requires a modern GPU on the streaming host, and the codec's five-to-tenfold bandwidth cost rules out anything short of a wired Gigabit connection on the client end.