VCDs playback requires device node
vcdsrc in GStreamer currently only supports playing back from block devices, and could fairly easily support playing back from images. What it will not support is playing back from directories.
$ ./disc /run/media/hadess/20121123_1310 ** Message: /run/media/hadess/20121123_1310 contains a Video CD. ** Message: MRL for directory is "vcd:///run/media/hadess/20121123_1310". $ ./disc ~/Videos/VCD.iso ** Message: /home/hadess/Videos/VCD.iso contains a Video CD. ** Message: MRL for directory is "vcd:///home/hadess/Videos/VCD.iso". $ mount | grep 20121123_1310 /home/hadess/Videos/VCD.iso on /run/media/hadess/20121123_1310 type iso9660 (ro,nosuid,nodev,relatime,norock,check=r,map=n,blocksize=2048,uid=1000,gid=1000,dmode=500,fmode=400,uhelper=udisks2)
./disc runs should have the same result instead, pointing to an image or block device, never to a directory.