Add Interactive Movie MatroskaScript commands

[robUx4]

Following the work on a VLC GSoC (Google Summer of Code) to bring interactive movie support to Matroska, it has become clear that the logic of "choice handling" needs to be handled in a Chapter Codec.

The Chapter Codec creates the list of choices that the player should "show" when entering the "chapter where the choice is made". The Chapter Codec then applies the selection of the user at the end of this "chapter where the choice is made".

The way the choices are shown to the user can vary. It could just be text that the player should show in a fancy way. It could be coupled with a button track (similar to the button track found in DVDs and used by the "DVD menu" chapter codec) that can dynamically highlight some areas of the video.

The proposed addition to MatroskaScript are:

• choice_variable = CreateChoice();
• choice_variable.SetText('some text', <BCP47 language>);
• choice_variable.SetOnSelected( <function call> );
• MakeDefaultChoice(a_choice_variable);

For now the only possible function call possible would be the GotoAndPlay( ChapterUID ) already existing in MatroskaScript.

[robUx4]

These commands do not provide support for Button Tracks interaction.