[alsa-devel] pcm_rate API question

[Rob Sykes]

Hello alsa devs,

There's an ongoing attempt to see if libsoxr-lsr can be used as a plug-in replacement for libsamplerate in pulseaudio and in alsa (libsoxr-lsr is designed with this usage in mind).

With pulseaudio, it seems to 'just work', but with alsa, it looks like there is a buffering problem.  Progress reports for this are here:

http://blog.ivitera.com/pavel/linux-audio/pulseaudio-with-ld_preloading-libsoxr-lsr

http://blog.ivitera.com/pavel/linux-audio/simple-use-of-libsoxr-lsr-in-alsa-using-ld_preload


AFAICT, the problem with alsa relates to the use of this function in pcm_rate.h:

typedef struct snd_pcm_rate_ops {
...
        void (*convert_s16)(void *obj, int16_t *dst, unsigned int dst_frames,
                            const int16_t *src, unsigned int src_frames);

Is there documentation available regarding the use of this function? For example, is the plugin obliged always to consume src_frames and generate dst_frames samples?  If so, how is the plugin expected to comply (say, if it's not been given enough input to generate that amount of output)?

TIA,
Rob