InputStreamAudio: fix channels error when decode stream

* InputStreamAudio: update constructor to indicate number of channels of
the CodecContext.
* AudioDesc: add getters for channels, sample rate and sample format.
AudioDesc: refactoring

* SetAudioParameters: use copy instead of reference for AVSampleFormat
(enum).
Merge pull request #3 from cchampet/dev_audioProcessing

Adding audio