Valve has announced the inclusion of the Pyrowave video codec, optimized for low-latency video streaming over high-bandwidth networks, in the beta version of the Steam client. The codec is added as an option in the Steam Remote Play service, allowing users to stream gameplay or mirror output to their system while playing on other devices. In the Linux version of Steam, the codec becomes available by enabling it in the SteamRT3 mode settings. The codec's implementation is written in C++ and is licensed under MPL.
The codec supports only intra-frame coding (intra-only), regardless of neighboring frames (all frames are keyframes; inter-frame compression is not used). This approach allows for very high image transmission accuracy and eliminates artifacts during motion and abrupt background changes. Discrete wavelet transformation using the CDF 9/7 filter, similar to JPEG2000 format, is applied to image encoding, along with trivial entropy coding that enables efficient parallel computations.
The codec is very demanding on bandwidth — compared to other streaming codecs, Pyrowave requires 5-10 times more traffic. It is recommended to use the codec for streaming and accessing games on a local network with connections to gigabit Ethernet ports. By default, the bitrate is automatically selected based on the content, but there’s a setting available for specifying an upper bitrate limit (acceptable values range from 100 to 500 Mbit/s) when the network bandwidth is limited.
Pyrowave is optimized for extremely fast encoding and decoding using GPU acceleration and is fully implemented in the form of compute shaders. With sufficient bandwidth (bitrate around ~200+ Mbit/s), the codec demonstrates minimal latencies of 0.1 ms at 1080p quality and 0.2 ms at 4K quality. To maintain stability against packet loss, Pyrowave uses isolated block encoding of 64×64.
HDR and color spaces YCbCr 4:2:0 and 4:4:4 are supported. HDR is automatically enabled when supported by both the host and client. The 4:4:4 color encoding format requires more resource-intensive computations and increases traffic, so it is disabled by default and is recommended for activation when streaming desktop content or enhancing text readability in videos.
Source: opennet.ru
