[nvda] Re: USB eSpeak

On 26 Apr, James Teh <jamie@xxxxxxxxxxx> wrote:

> There's something I don't quite understand. You said in a previous
> email that when in synchronous mode, to stop speech, one must return
> a certain value in the callback function. How often does the
> callback function get called?

As soon as the user-process has returned from the previous callback
(plus a short time for eSpeak to process the next buffer-full).

If the user-process is playing the sound, and waiting until play is
complete before returning from the callback function, then the
frequency of callbacks is proportional to the buffer size which you set
in espeak_Initialize().

> In order to have instantaneous silence, it would have ot be called
> every few samples. I assume it works fine, as you must be doing this
> for SAPI 5.

I use a buffer size of 100 mS (= 2205 samples).  But the Windows SAPI5
manager plays the sound, not eSpeak.  So it can stop the playing
immediately, irrespective of the buffer size.

How will stop-speaking work if you use a synchronous-playback mode? 
You give eSpeak a sentence and it espeak_Synthesize() doesn't return
until it's completed. Unlike asynchronous-playback (where you can call
espeak_Cancel()) or either retrieval mode (where you can return "abort"
to the callback) there's no way to interrupt it.  Can you kill the
thread and stop the speaking?

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