The "A silent voice" specials are two music videos of songs related to the anime. The animations seems to mostly be original scenes and of pretty good quality. The animation mainly contains the main two characters and Ishida's friend along with some shots of nature. In the first song I didn't understand the animation and whether it was supposed to tell a story but in the second song the animation has a clear story attached to it. At the very least it's something to watch while listening to the music. The songs themselves are alright and you'll probably recognise them from the movie. If youdidn't like the music in the movie then obviously you won't like this.

Overall you can watch this if you liked the music in the movie but you're not missing out on much if you decide not to watch these.