Find total number of files with certain extension and display their total in linux

In below example we will find total number of audio/video files and add their sizes to show total volume on disk.

find /folder/destination -type f -regex '.*\.\(mkv\|mp4\|wmv\|flv\|webm\|mov\|mp3\)' -exec du -ch {} + | grep total$
7.8G total

/folder/destination is destination of your folder inside which you want to calculate total size of audio/video files

To calculate total size any folder browse in that directory and run:

du sh