A rewrap case can need to transcode at specific moments:
* if there is an offset at the beginning
* if it continues with a generator at the end of the rewrap.

…ing case

Fix avTranscoder#165

Add properties of base class if the derived class override
getPropertiesAsVector (for Video and Audio).

Note: remove useless InputStreams clearBuffering call.

The streams analysis is done in the FileProperties, not in the
InputFile.

* It containes only references to the other properties (video,
audio...).
* Get the properties at the indicated stream index with only one
function.

Instead of the duration from the format.

Always need to create an InputFile to get the encofing profile from it,
but not necessary add it to our list of InputFile.