I know, i will add the leading `/`. Have tried, it also works.

Caching the file is not really necessary, because just the native `getMaxAmplitude()` method on the stream is needed. But i would be an alternative, though.
I browsed through the code which tries to access the file when recording is started, but couldn't find anything for this case.
As for now, i could say it works on the Nexus S 4.1.2 (non-root) and also Jenkins was able to start the `MediaRecorder` with this option.