Magic Seek is deprecated. Instead, use Binwalk:
nix-shell -p python3Packages.binwalk --run 'binwalk --extract catenation'
Magic Seek is unusably slow with its 10 kB/s seek speed best-case scenario. Binwalk contains its own magic implementation that is specifically optimized for seeks, which results in more than 3 orders of magnitude better performance over something like this.
Plus, Binwalk can also analyze, decompress, diff, and find high-entropy fragments in binary data. Try it!