ffmpeg: switch to new source repo

  # NOTICE: Always use this argument to override the version. Do not use overrideAttrs.

  version, # ffmpeg ABI version. Also declare this if you're overriding the source.

  hash ? "", # hash of the upstream source for the given ABI version

  source ? fetchgit {

    url = "https://git.ffmpeg.org/ffmpeg.git";

    rev = "n${version}";

  source ? fetchFromGitea {

    domain = "code.ffmpeg.org";

    owner = "FFmpeg";

    repo = "FFmpeg";

    tag = "n${version}";

    inherit hash;

  },

  # instead.

  withFullDeps ? ffmpegVariant == "full",

  fetchgit,

  fetchFromGitea,

  fetchpatch2,

  # Feature flags