This demo uses the Basis C++ transcoder (compiled to Javascript using Empscripten) and can work on all devices, though desktop may be preferred to create the files as it only accepts PNG input currently. The GPU format your current device is using is FORMAT. Scroll down to see all compute the stats and debug output for your image. Thanks to Evan Parker for providing webgl-texture-utils and this test bed, and Journie Ma-Johnson for expanding upon it and creating this demo you see today.

Debug:
If checked, debug info will output to stdout.
Compute Stats:
If checked, PSNR statistics will output to stdout.
sRGB:
If checked, the input is assumed to be in sRGB space. Be sure to set this correctly! (Examples: True on photos, albedo/spec maps, and false on normal maps.)
Mipmaps:
If checked, .basis file will generate with mipmaps.
UASTC:
If checked, encoder will output a UASTC texture (very high quality mode with larger file size), otherwise, an ETC1S texture.
ETC1S Quality:
Set quality of ETC1S quality level. Note that higher quality levels will result in larger file sizes, and longer load times.
Mipmap:
Use this to view a specific mipmap of the .basis file.

BASIS UNIVERSAL COMPRESSION DEMO