When I first read this code I thought somebody had forgot about the declared
sample rate and just assumed it to always be 48000 Hz in matroskademux.

Some days passed, and I was working on a opusparse bug when I again found the
48000 magic number. That made me suspicious. I tried encoding some audio at
24000 Hz. It worked, but why? I kept looking and finally I read the opusdec
code where the actual sample clipping was done. Then I knew and everything was
obvious.

This patch is for the me of the past who did not.