void merge_from (const Buffer& src, framecnt_t len, framecnt_t dst_offset = 0, framecnt_t src_offset = 0) {
const AudioBuffer* ab = dynamic_cast<const AudioBuffer*>(&src);
assert (ab);
accumulate_from (*ab, len, dst_offset, src_offset);
}
void merge_from (const Buffer& src, framecnt_t len, framecnt_t dst_offset = 0, framecnt_t src_offset = 0) {
const AudioBuffer* ab = dynamic_cast<const AudioBuffer*>(&src);
assert (ab);
accumulate_from (*ab, len, dst_offset, src_offset);
}