.SV4 video file won't play in VLC

I have a program called JDVR that is recording feeds from analog security cameras (BNC coectors). The directory where the DVR files are stored has several .SV4 files of various sizes (from 12 KB to 923 MB), but I caot play any of them.

I thought VLC should play them, but even the longest one (largest file) just stalls and won't play. We had a possible break-in over the weekend, so I really need these to play. Any help appreciated. Thanks