Indeed, libsidplay-fp's audio renderer expects buffer of 16-bit shorts and number of samples as input, AND returns number of samples. Thus, we need to divide and multiply the values accordingly. However, it also seems that some internal buffers in resid-fp are hardcoded to certain size, and using too big audio buffers cause overflows .. trying to compensate for that by limiting the amount of audio rendered. Unfortunately there are still memory corruptions.

XMMS-SID - SIDPlay input plugin for X MultiMedia System (XMMS)
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Matti 'ccr' Hämäläinen - author and maintainer of XMMS-SID

MD5 implementation (src/xs_md5.c) originally by Colin Plumb 1993,
released in "public domain". Modified for XMMS-SID by ccr.