snd_pcm_area_copy
snd_pcm_area_copy(&src_channels->area, 0, &dst_channels->area, 0, frames, plugin->src_format.format);
int snd_pcm_area_copy(const struct snd_pcm_channel_area *src_channel,
snd_pcm_area_copy(&src_channel->area, 0, &dst_channel->area, 0, frames, format);