Investigating some more, and this is what I can see when I drill down on in_mp3.dll, which belongs to AOL (Winamp). They were apparently comfortable enough to provide assembly information...
Where I placed the

is where the largest number of timer samples happened in that DLL.
Address Code Bytes Instruction Symbol Timer samples
0x7715e80 0x 51 push ecx 0
0x7715e81 0x 53 push ebx 0
0x7715e82 0x 55 push ebp DeleteAudioDecoder+11215 0.43
0x7715e83 0x 56 push esi DeleteAudioDecoder+11216 0.43
0x7715e84 0x 8B 70 24 mov esi,[eax+24h] DeleteAudioDecoder+11217 1.29
0x7715e87 0x 57 push edi DeleteAudioDecoder+11220 0.43
0x7715e88 0x 8B 78 1C mov edi,[eax+1ch] 0
0x7715e8b 0x 8B D7 mov edx,edi DeleteAudioDecoder+11224 0.43
0x7715e8d 0x C1 FA 03 sar edx,03h 0
0x7715e90 0x 83 E2 FE and edx,feh 0
0x7715e93 0x 66 0F B6 0C 16 movzx cx,byte [esi+edx] DeleteAudioDecoder+11232 0.43

0x7715e98 0x 66 0F B6 6C 16 01 movzx bp,byte [esi+edx+01h] DeleteAudioDecoder+11237 3
0x7715e9e 0x 66 C1 E1 08 shl cx,08h 0
0x7715ea2 0x 66 0B E9 or bp,cx DeleteAudioDecoder+11247 0.43
0x7715ea5 0x 66 8B DF mov bx,di 0
0x7715ea8 0x 66 83 E3 0F and bx,0fh 0
0x7715eac 0x 66 8B CB mov cx,bx 0
0x7715eaf 0x 66 D3 E5 shl bp,cl 0
0x7715eb2 0x 0F B7 CD movzx ecx,bp DeleteAudioDecoder+11263 1.29
0x7715eb5 0x 89 4C 24 10 mov [esp+10h],ecx DeleteAudioDecoder+11266 0.86
0x7715eb9 0x 8B CF mov ecx,edi 0
0x7715ebb 0x 83 E1 0F and ecx,0fh 0
0x7715ebe 0x BD 10 00 00 00 mov ebp,00000010h DeleteAudioDecoder+11275 0.86
0x7715ec3 0x 2B E9 sub ebp,ecx 0
0x7715ec5 0x 39 6C 24 18 cmp [esp+18h],ebp 0
0x7715ec9 0x 76 27 jbe $+29h (0x7715ef2) DeleteAudioDecoder+11286 1.29
0x7715ecb 0x 8B 48 08 mov ecx,[eax+08h] 0
0x7715ece 0x 49 dec ecx DeleteAudioDecoder+11291 0.86
0x7715ecf 0x 83 C2 02 add edx,02h 0
0x7715ed2 0x 23 CA and ecx,edx 0
0x7715ed4 0x 66 0F B6 54 0E 01 movzx dx,byte [esi+ecx+01h] 0
0x7715eda 0x 66 0F B6 0C 0E movzx cx,byte [esi+ecx] 0
0x7715edf 0x 66 C1 E1 08 shl cx,08h 0
0x7715ee3 0x 66 0B D1 or dx,cx 0
0x7715ee6 0x B1 10 mov cl,10h 0
0x7715ee8 0x 2A CB sub cl,bl 0
0x7715eea 0x 66 D3 EA shr dx,cl 0
0x7715eed 0x 66 09 54 24 10 or [esp+10h],dx DeleteAudioDecoder+11322 0.43
0x7715ef2 0x 8B 54 24 18 mov edx,[esp+18h] 0
0x7715ef6 0x 8B 48 0C mov ecx,[eax+0ch] DeleteAudioDecoder+11331 0.43
0x7715ef9 0x 01 50 18 add [eax+18h],edx DeleteAudioDecoder+11334 0.43
0x7715efc 0x 29 50 10 sub [eax+10h],edx 0
0x7715eff 0x 49 dec ecx 0
0x7715f00 0x 03 FA add edi,edx DeleteAudioDecoder+11341 0.43
0x7715f02 0x 23 F9 and edi,ecx DeleteAudioDecoder+11343 0.43
0x7715f04 0x 89 78 1C mov [eax+1ch],edi 0
0x7715f07 0x 0F B7 44 24 10 movzx eax,word [esp+10h] DeleteAudioDecoder+11348 0.43
0x7715f0c 0x 5F pop edi DeleteAudioDecoder+11353 0.43
0x7715f0d 0x 5E pop esi 0
0x7715f0e 0x B9 10 00 00 00 mov ecx,00000010h 0
0x7715f13 0x 2A CA sub cl,dl 0
0x7715f15 0x 5D pop ebp 0
0x7715f16 0x D3 E8 shr eax,cl DeleteAudioDecoder+11363 1.72
0x7715f18 0x 5B pop ebx 0
0x7715f19 0x 59 pop ecx DeleteAudioDecoder+11366 0.86
0x7715f1a 0x C2 04 00 retnd 0004h DeleteAudioDecoder+11367 0.43