flif.info claims: FLIF is a novel lossless image format which outperforms PNG, lossless WebP, lossless BPG and lossless JPEG2000 in terms of compression ratio
What we don't know is if the CPU usage is comparable to those formats. progressive decoding could be useful for us: the encoding is done in multiple passes, we could send the partial data after each pass and cancel later passes if a new refresh comes in.
Still no packages for Fedora, no development headers get installed, and the viewer doesn't build properly on Fedora..
FLIF development has stopped since FLIF is superceded by FUIF and then again by JPEG XL - created #2854
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/992