Update ffmpeg.rb

[Wicky2k8]

Needed for zvbi to function correctly (#105)

Taken from @Vincent-Dabouineau's tap (https://github.com/LesCanauxDiscrets/homebrew-tap/blob/master/Formula/ffmpeg.rb)

[slhck]

This only works when the non-default formula is installed, right? What happens when the user doesn't have that?

[Wicky2k8]

It won't work, but that's noted in the information on the main screen ("The ZVBI library has to be installed before running the FFmpeg formula.")

Anyways that issue already exists with the current setup, this just allows it to find zvbi if it is installed and the option is chosen (currently that fails)

[slhck]

In that case it would make sense to directly link to the other tap in the README, so that users will know from where they have to install the library.

Anyway, this makes sense, merging for now. Thanks!

[slhck]

Addressed in 1ffa61c

[retokromer]

I noticed that there are a few issues with this library, which is obviously no longer maintained. I guess it’s out of the scope of our formula to update also this.

Should we bump a revision?

[slhck]

If it was still maintained we might add it to the tap, but I agree it's out of scope.

You're right about the revision, will do so in a second.

[retokromer]

Please wait one minute.

[retokromer]

From my notes:

1. I guess, we should change:

  on_linux do
    depends_on "libxv"
    depends_on "gcc" if build.with? "rubberband"
  end

2. I am not sure that we need:

depends_on "texinfo" => :build