9.2 Text modes

We do not believe that all texts are of the same type. Often information about the general contents of file will aid synthesis greatly. For example in Latex files we do not want to here "left brace, backslash e m" before each emphasized word, nor do we want to necessarily hear formating commands. Festival offers a basic method for specifying customization rules depending on the mode of the text. By type we are following the notion of modes in Emacs and eventually will allow customization at a similar level.

Modes are specified as the third argument to the function tts. When using the Emacs interface to Festival the buffer mode is automatically passed as the text mode. If the mode is not supported a warning message is printed and the raw text mode is used.

Our initial text mode implementation allows configuration both in C++ and in Scheme. Obviously in C++ almost anything can be done but it is not as easy to reconfigure without recompilation. Here we will discuss those modes which can be fully configured at run time.

A text mode may contain the following

filter

A Unix shell program filter that processes the text file in some appropriate way. For example for email it might remove uninteresting headers and just output the subject, from line and the message body. If not specified, an identity filter is used.

init_function

This (Scheme) function will be called before any processing will be done. It allows further set up of tokenization rules and voices etc.

exit_function

This (Scheme) function will be called at the end of any processing allowing reseting of tokenization rules etc.

analysis_mode

If analysis mode is xml the file is read through the built in XML parser rxp. Alternatively if analysis mode is xxml the filter should an SGML normalising parser and the output is processed in a way suitable for it. Any other value is ignored.

These mode specific parameters are specified in the a-list held in tts_text_modes.

When using Festival in Emacs the emacs buffer mode is passed to Festival as the text mode.

Note that above mechanism is not really designed to be re-entrant, this should be addressed in later versions.

Following the use of auto-selection of mode in Emacs, Festival can auto-select the text mode based on the filename given when no explicit mode is given. The Lisp variable auto-text-mode-alist is a list of dotted pairs of regular expression and mode name. For example to specify that the email mode is to be used for files ending in .email we would add to the current auto-text-mode-alist as follows

(set! auto-text-mode-alist
      (cons (cons "\\.email$" 'email)
            auto-text-mode-alist))

If the function tts is called with a mode other than nil that mode overrides any specified by the auto-text-mode-alist. The mode fundamental is the explicit "null" mode, it is used when no mode is specified in the function tts, and match is found in auto-text-mode-alist or the specified mode is not found.

By convention if a requested text model is not found in tts_text_modes the file MODENAME-mode will be required. Therefore if you have the file MODENAME-mode.scm in your library then it will be automatically loaded on reference. Modes may be quite large and it is not necessary have Festival load them all at start up time.

Because of the auto-text-mode-alist and the auto loading of currently undefined text modes you can use Festival like

festival --tts example.email

Festival with automatically synthesize example.email in text mode email.

If you add your own personal text modes you should do the following. Suppose you’ve written an HTML mode. You have named it html-mode.scm and put it in /home/awb/lib/festival/. In your .festivalrc first identify you’re personal Festival library directory by adding it to lib-path.

(set! lib-path (cons "/home/awb/lib/festival/" lib-path))

Then add the definition to the auto-text-mode-alist that file names ending .html or .htm should be read in HTML mode.

(set! auto-text-mode-alist
      (cons (cons "\\.html?$" 'html)
            auto-text-mode-alist))

Then you may synthesize an HTML file either from Scheme

(tts "example.html" nil)

Or from the shell command line

festival --tts example.html

Anyone familiar with modes in Emacs should recognise that the process of adding a new text mode to Festival is very similar to adding a new buffer mode to Emacs.