(3 MB * 8192) / 240 seconds = 102.4 kilobits/second
I can confirm this problem -- mp3s created from flvs with ubuntu's version of ffmpeg were unplayable on a SanDisk Clip+. I used ffmpeg -i $i -ab 192k -ar 44100 $i.mp3, and also avconv -i $i -ab 192k -ar 44100 $i.mp3, and playing mp3s so created froze the player. I replaced /usr/bin/ffmpeg with the ffmpeg static binary downloaded from the link provided in post #7 in this thread, converted same flv files to mp3s, and they now play without freezing. I'm using Mint 13 Maya. I routinely use ffmpeg, and this problem just appeared within the last week or three, so perhaps there was a change to ubuntu's version of ffmpeg that broke something. I had also arrived at the solution of converting flv to mp3 with Audacity, which produced mp3s that worked.