`ARGV.value` is great.

```ruby
  option "with-mp4", "Built with support of mp4 output[l-smash, gpac]."

  case ARGV.value("with-mp4")
    when "l-smash"
      depends_on "l-smash"
    when "gpac"
      depends_on "gpac"
  end
```

However, in `install`, How can I get dependency on `l-smash` or `gpac`?

```ruby
    if build.with? "l-smash"
      args << "--disable-gpac"
    elsif build.with? "mp4=gpac"
      args << "--disable-lsmash"
    end
```