7. APIs

Flite is a library that we expected will be embedded into other applications. Included with the distribution is a small example executable that allows synthesis of strings of text and text files from the command line.

7.1 flite binary

The example flite binary may be suitable for very simple applications. Unlike Festival its start up time is very short (less that 25ms on a PIII 500MHz) making it practical (on larger machines) to call it each time you need to synthesize something.

flite TEXT OUTPUTTYPE

If TEXT contains a space it is treated as a string of text and converted to speech, if it does not contain a space TEXT is treated as a file name and the contents of that file are converted to speech. The option -t specifies TEXT is to be treat as text (not a filename) and -f forces treatment as a file. Thus

flite -t hello 

will say the word "hello" while

flite hello 

will say the content of the file `hello'. Likewise

flite "hello world."

will say the words "hello world" while

flite -f "hello world"

will say the contents of a file `hello world'. If no argument is specified text is read from standard input.

The second argument OUTPUTTYPE is the name of a file the output is written to, or if it is play then it is played to the audio device directly. If it is none then the audio is created but discarded, this is used for benchmarking. If OUTPUTTYPE is omitted, play is assumed. You can also explicitly set the outputtype with the -o flag.

flite -f doc/alice -o alice.wav

7.2 C example

Each voice in Flite is held in a structure, a pointer to which is returned by the voice registration function. In the standard distribution, the example diphone voice is cmu_us_kal.

Here is a simple C program that uses the flite library

#include "flite.h"

cst_voice *register_cmu_us_kal();

int main(int argc, char **argv)
{
    cst_voice *v;

    if (argc != 2)
    {
        fprintf(stderr,"usage: flite_test FILE\n");
        exit(-1);
    }

    flite_init();

    v = register_cmu_us_kal();

    flite_file_to_speech(argv[1],v,"play");

}

Assuming the shell variable FLITEDIR is set to the flite directory the following will compile the system (with appropriate changes for your platform if necessary).

gcc -Wall -g -o flite_test flite_test.c -I$FLITEDIR/include -L$FLITEDIR/lib 
    -lflite_cmu_us_kal -lflite_usenglish -lflite_cmulex -lflite -lm

7.3 Public Functions

Although, of course you are welcome to call lower level functions, there a few key functions that will satisfy most users of flite.

void flite_init(void);

This must be called before any other flite function can be called. As of Flite 1.1, it actually does nothing at all, but there is no guarantee that this will remain true.

cst_wave *flite_text_to_wave(const char *text,cst_voice *voice);

Returns a waveform (as defined in `include/cst_wave.h') synthesized from the given text string by the given voice.

float flite_file_to_speech(const char *filename, cst_voice *voice, const char *outtype);

synthesizes all the sentences in the file `filename' with given voice. Output (at present) can only reasonably be, play or none.

float flite_text_to_speech(const char *text, cst_voice *voice, const char *outtype);

synthesizes the text in string point to by text, with the given voice. outtype may be a filename where the generated waveform is written to, or "play" and it will be sent to the audio device, or "none" and it will be discarded. The return value is the number of seconds of speech generated.

cst_utterance *flite_synth_text(const char *text,cst_voice *voice);

synthesize the given text with the given voice and returns an utterance from it for further processing and access.

cst_utterance *flite_synth_phones(const char *phones,cst_voice *voice);

synthesize the given phones with the given voice and returns an utterance from it for further processing and access.

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