Please describe the problem:
Playing MP3 files with low bit-rates whilst Cross-Fader is enabled causes the CPU to be used heavily and temperatures to run high.

Originally this came to light whilst playing large MP3 audio-books (in this case a 10-hour file - 286.9 MB). It causes Rhythmbox to keep the CPU(s) under heavy load and drives temperatures towards the high-end of their range. Expected normal temperature is 52C but I'm seeing 64-69C as one or other core is being driven hard constantly.

System Monitor Processes tab reports Rhythmbox is sleeping and using 32% CPU. CPU history tab shows one CPU at 60%, the other around 8%. Occasionally the load swaps cores (presumably as threads start/stop).

As soon as playback is paused both cores drop to 2% usage and the temperature rapidly falls back to normal levels.

I've found that MP3 tracks of any length that are 32kbps or 64kbps (mono or stereo) cause this whilst 128kbps tracks are okay. Most of the audio-books are 32 or 64 kbps although I found one that was 128kbps, and it played without the CPU load issue. Almost all my music files are 128kbps or higher.

Steps to reproduce:
1. Ensure Cross-Fader is enabled
2. Choose a low bit-rate MP3 (audio books are favourite) 
3. Play file


Actual results:
CPU usage & goes very high and CPU temperatures rise to end end of range.

Expected results:
CPU usage to barely change, and temperature to remain low

Does this happen every time?
With Cross-Fader disabled the problem doesn't occur

Other information:
Originally reported as Ubuntu bug #141390

https://bugs.launchpad.net/ubuntu/+bug/141390