[alsa-devel] Question about the buffer length in the transfer callback of the PCM External Plugin

[Bach, Andrea]

Hello,

how can I change the size that is provided inside the „transfer“-callback of an external PCM plugin?

Background:
I need to write a filter plugin and I have to use for processing a chunk size of power of two (32, 64, or 128 bytes … that’s because of the use of FFT). But I get inside the transfer callback a buffer of length 1000. That would be ok if I could just return let's say  960 bytes – but after some struggling I have some doubt about it because I got the impression that ALSA cannot change the bitrate inside such a plugin – the documentation states it could not change the sample rate – but actually how can I return less or more bytes – so maybe the bitrate should also be constant? Maybe I misunderstood the concepts of ALSA completely?

Kind regards

Dr. A. Bach, Software-Entwicklung Simulatoren
DFS Deutsche Flugsicherung GmbH
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