squeezelite: use ffmpeg 4

[samdoshi]

see #120705

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 122336 at 8323b60 run on x86_64-linux 1

1 package built successfully:

• squeezelite

1 suggestion:

• warning: unclear-gpl

  gpl3 is a deprecated license, please check if project uses gpl3Plus or gpl3Only and change meta.license accordingly.

  Near pkgs/applications/audio/squeezelite/default.nix:66:5:

     |
  66 |     license = with licenses; [ gpl3 ] ++ optional dsdSupport bsd2;
     |     ^