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28. API

If you wish to use Festival within some other application there are a number of possible interfaces.

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28.1 Scheme API

Festival includes a full programming language, Scheme (a variant of Lisp) as a powerful interface to its speech synthesis functions. Often this will be the easiest method of controlling Festival’s functionality. Even when using other API’s they will ultimately depend on the Scheme interpreter.

Scheme commands (as s-expressions) may be simply written in files and interpreted by Festival, either by specification as arguments on the command line, in the interactive interpreter, or through standard input as a pipe. Suppose we have a file ‘hello.scm’ containing

;; A short example file with Festival Scheme commands
(voice_rab_diphone) ;; select Gordon
(SayText "Hello there")
(voice_don_diphone) ;; select Donovan
(SayText "and hello from me")

From the command interpreter we can execute the commands in this file by loading them

festival> (load "hello.scm")

Or we can execute the commands in the file directly from the shell command line

unix$ festival -b hello.scm

The ‘-b’ option denotes batch operation meaning the file is loaded and then Festival will exit, without starting the command interpreter. Without this option ‘-b’ Festival will load ‘hello.scm’ and then accept commands on standard input. This can be convenient when some initial set up is required for a session.

Note one disadvantage of the batch method is that time is required for Festival’s initialisation every time it starts up. Although this will typically only be a few seconds, for saying short individual expressions that lead in time may be unacceptable. Thus simply executing the commands within an already running system is more desirable, or using the server/client mode.

Of course its not just about strings of commands, because Scheme is a fully functional language, functions, loops, variables, file access, arithmetic operations may all be carried out in your Scheme programs. Also, access to Unix is available through the system function. For many applications directly programming them in Scheme is both the easiest and the most efficient method.

A number of example Festival scripts are included in ‘examples/’. Including a program for saying the time, and for telling you the latest news (by accessing a page from the web). Also see the detailed discussion of a script example in See section POS Example.

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28.2 Shell API

The simplest use of Festival (though not the most powerful) is simply using it to directly render text files as speech. Suppose we have a file ‘hello.txt’ containing

Hello world.  Isn't it excellent weather
this morning.

We can simply call Festival as

unix$ festival --tts hello.txt

Or for even simpler one-off phrases

unix$ echo "hello " | festival --tts

This is easy to use but you will need to wait for Festival to start up and initialise its databases before it starts to render the text as speech. This may take several seconds on some machines. A socket based server mechanism is provided in Festival which will allow a single server process to start up once and be used efficiently by multiple client programs.

Note also the use of Sable for marked up text, see section XML/SGML mark-up. Sable allows various forms of additional information in text, such as phrasing, emphasis, pronunciation, as well as changing voices, and inclusion of external waveform files (i.e. random noises). For many application this will be the preferred interface method. Other text modes too are available through the command line by using auto-text-mode-alist.

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28.3 Server/client API

Festival offers a BSD socket-based interface. This allows Festival to run as a server and allow client programs to access it. Basically the server offers a new command interpreter for each client that attaches to it. The server is forked for each client but this is much faster than having to wait for a Festival process to start from scratch. Also the server can run on a bigger machine, offering much faster synthesis.

Note: the Festival server is inherently insecure and may allow arbitrary users access to your machine.

Every effort has been made to minimise the risk of unauthorised access through Festival and a number of levels of security are provided. However with any program offering socket access, like httpd, sendmail or ftpd there is a risk that unauthorised access is possible. I trust Festival’s security enough to often run it on my own machine and departmental servers, restricting access to within our department. Please read the information below before using the Festival server so you understand the risks.

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28.3.1 Server access control

The following access control is available for Festival when running as a server. When the server starts it will usually start by loading in various commands specific for the task it is to be used for. The following variables are used to control access.


A number identifying the inet socket port. By default this is 1314. It may be changed as required.


If nil no logging takes place, if t logging is printed to standard out and if a file name log messages are appended to that file. All connections and attempted connections are logged with a time stamp and the name of the client. All commands sent from the client are also logged (output and data input is not logged).


If non-nil it is used to identify which machines are not allowed access to the server. This is a list of regular expressions. If the host name of the client matches any of the regexs in this list the client is denied access. This overrides all other access methods. Remember that sometimes hosts are identified as numbers not as names.


If this is non-nil only machines whose names match at least one of the regexs in this list may connect as clients. Remember that sometimes hosts are identified as numbers not as names, so you should probably exclude the IP number of machine as well as its name to be properly secure.


If this is non-nil, the client must send this passwd to the server followed by a newline before access is given. This is required even if the machine is included in the access list. This is designed so servers for specific tasks may be set up with reasonable security.

(set_server_safe_functions FUNCNAMELIST)

If called this can restrict which functions the client may call. This is the most restrictive form of access, and thoroughly recommended. In this mode it would be normal to include only the specific functions the client can execute (i.e. the function to set up output, and a tts function). For example a server could call the following at set up time, thus restricting calls to only those that ‘festival_client--ttw uses.

        '(tts_return_to_client tts_text tts_textall Parameter.set))

Its is strongly recommend that you run Festival in server mode as userid nobody to limit the access the process will have, also running it in a chroot environment is more secure.

For example suppose we wish to allow access to all machines in the CSTR domain except for holmes.cstr.ed.ac.uk and adam.cstr.ed.ac.uk. This may be done by adding the following two commands to a file e.g. server.scm

(set! server_deny_list '("holmes\\.cstr\\.ed\\.ac\\.uk" 
(set! server_access_list '("[^\\.]*\\.cstr\\.ed\\.ac\\.uk"))

and them running the command

festival PATH_TO/server.scm --server

This is not complete though as when DNS is not working holmes and adam will still be able to access the server (but if our DNS isn’t working we probably have more serious problems). However the above is secure in that only machines in the domain cstr.ed.ac.uk can access the server, though there may be ways to fix machines to identify themselves as being in that domain even when they are not.

By default Festival in server mode will only accept client connections for localhost.

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28.3.2 Client control

An example client program called ‘festival_client’ is included with the system that provides a wide range of access methods to the server. A number of options for the client are offered.


The name (or IP number) of the server host. By default this is ‘localhost’ (i.e. the same machine you run the client on).


The port number the Festival server is running on. By default this is 1314.

--output FILENAME

If a waveform is to be synchronously returned, it will be saved in FILENAME. The --ttw option uses this as does the use of the Festival command utt.send.wave.client. If an output waveform file is received by ‘festival_client’ and no output file has been given the waveform is discarded with an error message.

--passwd PASSWD

If a passwd is required by the server this should be stated on the client call. PASSWD is sent plus a newline before any other communication takes places. If this isn’t specified and a passwd is required, you must enter that first, if the --ttw option is used, a passwd is required and none specified access will be denied.

--prolog FILE

FILE is assumed to be contain Festival commands and its contents are sent to the server after the passwd but before anything else. This is convenient to use in conjunction with --ttw which otherwise does not offer any way to send commands as well as the text to the server.


If an output waveform file is to be used this specified the output type of the file. The default is nist, but, ulaw, riff, ulaw and others as supported by the Edinburgh Speech Tools Library are valid. You may use raw too but note that Festival may return waveforms of various sampling rates depending on the sample rates of the databases its using. You can of course make Festival only return one particular sample rate, by using after_synth_hooks. Note that byte order will be native machine of the client machine if the output format allows it.


Text to wave is an attempt to make festival_client useful in many simple applications. Although you can connect to the server and send arbitrary Festival Scheme commands, this option automatically does what is probably what you want most often. When specified this options takes text from the specified file (or stdin), synthesizes it (in one go) and saves it in the specified output file. It basically does the following

(Parameter.set 'Wavefiletype '<output type>)
(tts_textall "
<file/stdin contents>

Note that this is best used for small, single utterance texts as you have to wait for the whole text to be synthesized before it is returned.

--aucommand COMMAND

Execute COMMAND of each waveform returned by the server. The variable FILE will be set when COMMAND is executed.


So that the delay between the text being sent and the first sound being available to play, this option in conjunction with --ttw causes the text to be synthesized utterance by utterance and be sent back in separated waveforms. Using --aucommand each waveform my be played locally, and when ‘festival_client’ is interrupted the sound will stop. Getting the client to connect to an audio server elsewhere means the sound will not necessarily stop when the ‘festival_client’ process is stopped.


With each command being sent to Festival a Lisp return value is sent, also Lisp expressions may be sent from the server to the client through the command send_client. If this option is specified the Lisp expressions are printed to standard out, otherwise this information is discarded.

A typical example use of ‘festival_client’ is

festival_client --async --ttw --aucommand 'na_play $FILE' fred.txt

This will use ‘na_play’ to play each waveform generated for the utterances in ‘fred.txt’. Note the single quotes so that the $ in $FILE isn’t expanded locally.

Note the server must be running before you can talk to it. At present Festival is not set up for automatic invocations through ‘inetd’ and ‘/etc/services’. If you do that yourself, note that it is a different type of interface as ‘inetd’ assumes all communication goes through standard in/out.

Also note that each connection to the server starts a new session. Variables are not persistent over multiple calls to the server so if any initialization is required (e.g. loading of voices) it must be done each time the client starts or more reasonably in the server when it is started.

A PERL festival client is also available in ‘festival/examples/festival_client.pl

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28.3.3 Server/client protocol

The client talks to the server using s-expression (Lisp). The server will reply with a number of different chunks until either OK is returned or ER (on error). The communication is synchronous, each client request can generate a number of waveform (WV) replies and/or Lisp replies (LP) and will be terminated with an OK (or ER). Lisp is used as it has its own inherent syntax that Festival can already parse.

The following pseudo-code will help define the protocol as well as show typical use

      ack = read three character acknowledgemnt
      if (ack == "WV\n")
         read a waveform
      else if (ack == "LP\n")
         read an s-expression
      else if (ack == "ER\n")
         an error occurred, break;
   while ack != "OK\n"

The server can send a waveform in an utterance to the client through the function utt.send.wave.client. The server can send a lisp expression to the client through the function TO BE DONE.

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28.4 C/C++ API

As well as offerening an interface through Scheme and the shell some users may also wish to embedd Festival within their own C++ programs. A number of simply to use high level functions are available for such uses.

In order to use Festival you must include ‘festival/src/include/festival.h’ which in turn will include the necessary other include files in ‘festival/src/include’ and ‘speech_tools/include’ you should ensure these are included in the include path for you your program. Also you will need to link your program with ‘festival/src/lib/libFestival.a’, ‘speech_tools/lib/libestools.a’, ‘speech_tools/lib/libestbase.a’ and ‘speech_tools/lib/libeststring.a’ as well as any other optional libraries such as net audio.

The main external functions available for C++ users of Festival are.

void festival_initialize(int load_init_files,int heapsize);

This must be called before any other festival functions may be called. It sets up the synthesizer system. The first argument if true, causes the system set up files to be loaded (which is normally what is necessary), the second argument is the initial size of the Scheme heap, this should normally be 210000 unless you envisage processing very large Lisp structures.

int festival_say_file(const EST_String &filename);

Say the contents of the given file. Returns TRUE or FALSE depending on where this was successful.

int festival_say_text(const EST_String &text);

Say the contents of the given string. Returns TRUE or FALSE depending on where this was successful.

int festival_load_file(const EST_String &filename);

Load the contents of the given file and evaluate its contents as Lisp commands. Returns TRUE or FALSE depending on where this was successful.

int festival_eval_command(const EST_String &expr);

Read the given string as a Lisp command and evaluate it. Returns TRUE or FALSE depending on where this was successful.

int festival_text_to_wave(const EST_String &text,EST_Wave &wave);

Synthesize the given string into the given wave. Returns TRUE or FALSE depending on where this was successful.

Many other commands are also available but often the above will be sufficient.

Below is a simple top level program that uses the Festival functions

int main(int argc, char **argv)
    EST_Wave wave;
    int heap_size = 210000;  // default scheme heap size
    int load_init_files = 1; // we want the festival init files loaded


    // Say simple file

    // Say some text;
    festival_say_text("hello world");

    // Convert to a waveform
    festival_text_to_wave("hello world",wave);

    // festival_say_file puts the system in async mode so we better
    // wait for the spooler to reach the last waveform before exiting
    // This isn't necessary if only festival_say_text is being used (and
    // your own wave playing stuff)

    return 0;

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28.5 C only API

A simpler C only interface example is given inf ‘festival/examples/festival_client.c’. That interface talks to a festival server. The code does not require linking with any other EST or Festival code so is much smaller and easier to include in other programs. The code is missing some functionality but not much consider how much smaller it is.

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28.6 Java and JSAPI

Initial support for talking to a Festival server from java is included from version 1.3.0 and initial JSAPI support is included from 1.4.0. At present the JSAPI talks to a Festival server elsewhere rather than as part of the Java process itself.

A simple (Pure) Java festival client is given ‘festival/src/modules/java/cstr/festival/Client.java’ with a wraparound script in ‘festival/bin/festival_client_java’.

See the file ‘festival/src/modules/java/cstr/festival/jsapi/ReadMe’ for requirements and a small example of using the JSAPI interface.

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