On Mon, Oct 31, 2016 at 02:11:17PM -0400, Fernando Rodriguez wrote: > On Mon, Oct 31, 2016 at 09:01:02AM +0000, Bach, Andrea wrote: > > 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? > > > > Yes. > You're working with raw PCM data, so the bitrate (bits per second) is > constant ((bit_depth/8) * samplerate * channels). The term usually > refers to compressed audio streams. Oops, that was in bytes. It's bitdepth * samplerate * channels. > > I haven't done this but by looking at the definition for the transfer > callback it looks pretty standard. It returns snd_pcm_sframes_t so I > suppose you can write less than *size* frames and return what was > actually written. It is signed so a negative value would indicate an > error. So you'll probably have to buffer any leftovers and write them on > the next call. That's not the same as changing the framerate because > at the end of the pipeline alsa will take care of playing it at the > right rate). > > That should clear some of the confussion. You'll probably have to look > at alsa-lib or some plugin's source code for more details. > > > > Kind regards > > > > Dr. A. Bach, Software-Entwicklung Simulatoren > > DFS Deutsche Flugsicherung GmbH > > Forschungszentrum > > Am DFS-Campus 5 > > 63225 Langen > > 06103-707-5709 > > > > DFS Deutsche Flugsicherung GmbH > > Am DFS-Campus > > D - 63225 Langen > > > > Tel.: +49-(0)6103-707-0 > > > > Sitz der Gesellschaft: Langen/Hessen > > Zuständiges Registergericht: AG Offenbach am Main, HRB 34977 > > Vorsitzende des Aufsichtsrats: Dr. Martina Hinricher > > Geschäftsführer: Prof. Klaus-Dieter Scheurle (Vors.), Robert Schickling, Dr. Michael Hann > > > > Internet: http://www.dfs.de > > Public-Key der DFS: http://www.dfs.de/dfs/public_key.asc > > _______________________________________________ > > Alsa-devel mailing list > > Alsa-devel@xxxxxxxxxxxxxxxx > > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel > > -- > Fernando Rodriguez -- Fernando Rodriguez _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
