bugfix with mp3 codec choose

Was wrong choose of "mp3" when "libmp3lame" available.

$codecs = array_keys($this->getCodecs('audio'));
//.... now $codecs is array of names, not name=>value, so rihgt way to check is:
$audio_codec = in_array('libmp3lame',$codecs) ? 'libmp3lame' : 'mp3';