I was poking about inside Mozilla's big WebXR demo to see how it was made.
https://mixedreality.mozilla.org/hello-webxr/
Most of the assets are xxx.basis files. ".basis" I had never heard of a dot basis file and not much came up on the internet.
Digging deeper I found a compiled Web Assembly Library and a javascript library wrapper for it.
60935 basis_transcoder.js
367268 basis_transcoder.wasm
They also used Draco which is also interesting for 3D object compression.
In further searching it's starting to look like this basis codec is going to be a standard part of three.js and therefore aframe.io for web based VR development.
Basis Universal GPU Texture Compression
texture video compression system that outputs a highly
compressed intermediate file format (.basis) that can be quickly transcoded to
a wide variety of GPU texture compression formats.
basis_universal
Basis Universal Supercompressed GPU Texture Codec
Basis Universal is a "supercompressed" GPU texture compression system that outputs a highly compressed intermediate file format (.basis) that can be quickly transcoded to a very wide variety of GPU compressed and uncompressed pixel formats: ASTC 4x4 L/LA/RGB/RGBA, PVRTC1 4bpp RGB/RGBA, PVRTC2 RGB/RGBA, BC7 mode 6 RGB, BC7 mode 5 RGB/RGBA, BC1-5 RGB/RGBA/X/XY, ETC1 RGB, ETC2 RGBA, ATC RGB/RGBA, ETC2 EAC R11 and RG11, FXT1 RGB, and uncompressed raster image formats 8888/565/4444.
The system now supports two modes: a high quality mode which is internally based off the UASTC compressed texture format, and the original lower quality mode which is based off a subset of ETC1 called "ETC1S". UASTC is for extremely high quality (similar to BC7 quality) textures, and ETC1S is for very small files. The ETC1S system includes built-in data compression, while the UASTC system includes an optional Rate Distortion Optimization (RDO) post-process stage that conditions the encoded UASTC texture data in the .basis file so it can be more effectively LZ compressed by the end user. More technical details about UASTC integration are here.
Basis files support non-uniform texture arrays, so cubemaps, volume textures, texture arrays, mipmap levels, video sequences, or arbitrary texture "tiles" can be stored in a single file. The compressor is able to exploit color and pattern correlations across the entire file, so multiple images with mipmaps can be stored very efficiently in a single file.
The system's bitrate depends on the quality setting and image content, but common usable ETC1S bitrates are .3-1.25 bits/texel. ETC1S .basis files are typically 10-25% smaller than using RDO texture compression of the internal texture data stored in the .basis file followed by LZMA. For UASTC files, the bitrate is fixed at 8bpp, but with RDO post-processing and user-provided LZ compression on the .basis file the effective bitrate can be as low as 2bpp for video or for individual textures approximately 4-6bpp.
The transcoder has been fuzz tested using zzuf.
So far, we've compiled the code using MSVS 2019, under Ubuntu x64 using cmake with either clang 3.8 or gcc 5.4, and emscripten 1.35 to asm.js. (Be sure to use this version or later of emcc, as earlier versions fail with internal errors/exceptions during compilation.) The compressor is multithreaded by default, but this can be disabled using the -no_multithreading command line option. The transcoder is currently single threaded.
Basis Universal supports "skip blocks" in ETC1S compressed texture arrays, which makes it useful for basic compressed texture video applications. Note that Basis Universal is still at heart a GPU texture compression system, not a video codec, so bitrates will be larger than even MPEG1.
Important Usage Notes
Probably the most important concept to understand about Basis Universal before using it: The system supports two very different universal texture modes: The original "ETC1S" mode is low/medium quality, but the resulting file sizes are very small because the system has built-in compression for ETC1S texture format files. This is the command line encoding tool's default mode. ETC1S textures work best on images, photos, map data, or albedo/specular/etc. textures, but don't work as well on normal maps. There's the second "UASTC" mode, which is significantly higher quality (near-BC7 grade), and is usable on all texture types including complex normal maps. UASTC mode purposely does not have built-in file compression like ETC1S mode does, so the resulting files are quite large (8-bits/texel - same as BC7) compared to ETC1S mode. The UASTC encoder has an optional Rate Distortion Optimization (RDO) encoding mode (implemented as a post-process over the encoded UASTC texture data), which lowers the output data's entropy in a way that results in better compression when UASTC .basis files are compressed with Deflate/Zstd, etc. In UASTC mode, you must losslessly compress the file yourself.
Basis Universal is not an image compression codec. It's a texture compression codec. It can be used just like an image compression codec, but that's not the only use case. Here's a good intro to GPU texture compression. If you're looking to primarily use the system as an image compression codec on sRGB photographic content, use the default ETC1S mode, because it has built-in compression.
The "-q X" option controls the output quality in ETC1S mode. The default is quality level 128. "-q 255" will increase quality quite a bit. If you want even higher quality, try "-max_selectors 16128 -max_endpoints 16128" instead of -q. -q internally tries to set the codebook sizes (or the # of quantization intervals for endpoints/selectors) for you. You need to experiment with the quality level on your content.
For tangent space normal maps, you should separate X into RGB and Y into Alpha, and provide the compressor with 32-bit/pixel input images. Or use the "-separate_rg_to_color_alpha" command line option which does this for you. The internal texture format that Basis Universal uses (ETC1S) doesn't handle tangent space normal maps encoded into RGB well. You need to separate the channels and recover Z in the pixel shader using z=sqrt(1-x^2-y^2).
3rd party code dependencies
The stand-alone transcoder (in the "transcoder" directory) is a single .cpp source file library which has no 3rd party code dependencies.
The encoder uses lodepng for loading and saving PNG images, which is Copyright (c) 2005-2019 Lode Vandevenne. It uses the zlib license. It also uses apg_bmp for loading BMP images, which is Copyright 2019 Anton Gerdelan. It uses the Apache 2.0 license.
The encoder uses tcuAstcUtil.cpp, from the Android drawElements Quality Program (deqp) Testing Suite, for unpacking the transcoder's ASTC output for testing/validation purposes. This code is Copyright 2016 The Android Open Source Project, and uses the Apache 2.0 license. We have modified the code so it has no external dependencies, and disabled HDR support.
This package uses BASIS and discusses is a little.
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