I’m not quite sure what you mean exactly. You can set showVideoDescripton="true"
to view the description as long as YouTube is sending it.
If there is a description it comes a) automatically shortened by YT and b) as plain text. As far as I can see it also does not contain carriage return characters \r or new line characters \n. So detecting separate lines is not possible.
And the plugin itself does not have some kind of filter or hook that can be applied to the content easily. You would either have to use Javascript to, for example, cut off the text after a certain number of characters/words. Or you would have to write your own PHP template.
...
/* Search YouTube. */
$results = $RytvAPI->searchYouTube( $data );
/* Custom PHP Template */
foreach( $results as $video ) {
...do your own operations...
}