Manage "rewrap" of stream in case of demultiplexing

* Manage the case like ffmpeg application: impossible to demultiplexing and rewrap a stream. So if the user wants to extract a channel from an audio stream, but does not give an output profile, we create a profile from the input, and we transcode. The output file has the same encoder as input (but only one channel), and the process has been transparent for the user.
* Transcoder: throw exception when user add an invalid stream (silent stream with no profile for example).