On Fri, 2009-07-24 at 23:35 +0200, Ulrich Lorenz Schlüter wrote: The template version of p() works just like the non-template version, it takes a uint32_t port index argument and returns a pointer to the buffer for that port. The only difference is that while the non-template version returns the buffer pointer as a pointer-to-float, the template version returns it as a pointer-to-T, where T is the template parameter. So in order to get the MIDI event input buffer for the port with index 6 you do LV2_Event_Buffer* inbuf = p<LV2_Event_Buffer>(6); or, equivalently LV2_Event_Buffer* inbuf = reinterpret_cast<LV2_Event_Buffer*>(p(6)); What you are doing above is to first get the buffer as a pointer-to-float although the buffer really contains an LV2_Event_Buffer, then dereference it to get some garbage float value, then truncate that float value to an uint32_t and pass it as the index parameter to p<LV2_Event_Buffer>(). This will cause undefined behaviour. It could crash with a segmentation fault, it could give you garbage MIDI events or it could do nothing at all. --ll