On Fri, 27 Jul 2007, stan wrote:
I really want to avoid rate resampling if I can, while format conversion has to occur somewhere in order to match the hardware in most cases. I assume that any format conversion alsa does is at least as good as one I would do myself. While the rate
Not really. If application knows all things, the final code might be much more optimized. Alsa-lib has all plugins universal (thus mostly unoptimized). For example - attenuation + sample conversion can be implemented together, but alsa-lib has two plugins - it means two iteration over same data.
resampling can introduce throughput issues and inaccuracies in the sound stream.
I answered this numerous times on this list. We have a function to notify the plugins that resampling should be avoided - it's snd_pcm_hw_params_set_rate_resample().
hw:x,y,z - native device without any conversions plughw:x,y,z - device trying to do all conversions for applications default - default device with all conversions (mostly pointing to plughw:x,y,z)
And yes, plugin doing all conversions is named "plug". So anywhere where "plug" plugin is used, other plugins - including the rate plugin - can be dynamically inserted to satisfy application requirements.
Jaroslav
----- Jaroslav Kysela perex@suse.cz Linux Kernel Sound Maintainer ALSA Project, SUSE Labs