Siwon Kang authored Apr 07, 2020 and Thibault Saunier committed Apr 07, 2020

For the use of matroskademux plugin, the PAD template has changed to
video_%u and audio_%u which generate video_0 and audio_0, respectively.
So the current example using old pad names(video_00/audio_00) causes the
failure in linking pads. This patch changes the pad names into correct
ones.