alsa resampler comstraints.

alsa resampler comstraints.

[James Courtier-Dutton]

Hi,

I want to document some of the constraints of the alsa resampler.
Here is what I understand, and I would like someone to verify my 
statements before I document them.

1) The buffer and period sizes for the sound card hardware to resampler 
are limited to the max buffer and period sizes available on the 
hardware. As a result, the available buffer and period sizes vary 
depending on hardware utilised.
2) The resampler converts one hardware period size at a time. This 
results in the buffer and period size constraints explained in (1) 
arriving at the application as a direct ratio of source and destination 
sample rate.
e.g. hardware has 2 periods of 1024 frames running at 48000 Hz.
application will see 2 periods of 1024 * 44100 / 48000 = 940.8. This is 
rounded down to 940 frames. So the user application sees 2 periods of 
940 frames.
If user space asks for 2 periods of 1024 at 44100 hz it will fail.


The above 2 points were true some time ago. Has anything changed?


Kind Regards

James


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Re: alsa resampler comstraints.

[Clemens Ladisch]

James Courtier-Dutton wrote:
> I want to document some of the constraints of the alsa resampler.
> Here is what I understand, and I would like someone to verify my 
> statements before I document them.
> 
> 1) The buffer and period sizes for the sound card hardware to resampler 
> are limited to the max buffer and period sizes available on the 
> hardware. As a result, the available buffer and period sizes vary 
> depending on hardware utilised.

Yes.  This is true for most of the plugins.

> 2) The resampler converts one hardware period size at a time. This 
> results in the buffer and period size constraints explained in (1) 
> arriving at the application as a direct ratio of source and destination 
> sample rate.

Yes.

> The above 2 points were true some time ago. Has anything changed?

That part of the resampler hasn't changed.


Regards,
Clemens

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