Some urls from the French version of the page could download the German version.
Also instead of extracting the json url from the webpage, build it to skip the download
A string statement is not a docstring if it doesn't occur right at the top
of modules, functions, class definitions etc.
This patch fixes it.
Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
Each source of videos have a different extraction process, they are in different methods of the extractor.
Changed the extension of videos from mp4 to flv.