[asterisk-dev] adjusting the playback speed of voicemail messages.

[Steve Underwood]

Steven S. Critchfield wrote:
> ----- "Michael Grigoni" <michael.grigoni at cybertheque.org> wrote:
>   
>> John Todd wrote:
>>
>> <snip>
>>     
>
>
>   
>> This thread got me to do a quick search for implementations of
>> variable speech control (hopefully public domain or open source)
>> but not much is out there.  U.S. Patent filing 4,864,620 contains
>> MS C 4.0 code for an implementation that should be testable on
>> a DOS machine.
>>     
>
> I do suggest you go look at what kind of damages can be awarded now that you have found a patent and I am assuming due to the code version referenced, it is a still valid patent.
>
> Knowing that you infringe a patent can cause triple the damage award. 
>
> You will have to find a different way, and specifically the way patent law works, DO NOT got looking for patents to ease your work. unknowingly infinging a patent is a sign of an obvious patent and reduces your exposure during the potential lawsuit.
>   
Duh! look at the dates. That patent has long expired. Its fair game. 
However, its far from the best way to do things.

Watch out for code using PSOLA (France Telecom has a patent on that, 
which I think is a kinda dumb patent) or WSOLA (the basic idea should be 
in the clear, but I believe there are variants which are saddled with 
patents). The variable speed code in spandsp uses a technique which is 
in the clear, gives good quality, and is reasonably light on compute 
demands.

Steve