ffmpeg: convert dv Movie File to mp4

I have an old file called ‘faces’ (no extension) and although quicktime cannot open it, VLC can open the video file no problem. When viewing a folder in list view containing this file, it is listed as a file with type “dv Movie”. I tried to convert it with ffmpeg but the output file was only a few kb and could not be viewed. I tried:
ffmpeg -i faces faces.mp4