A mishmash is a video comprised of clips that seem to have very little to do with each other. This is different from a mashup which is a video of clips that generally have a common theme. Mishmashes are often failed attempts at creating mashups due to poor editing skills or a lack of time.
Mishmash: a video that contains clips of grazing horses, Barack Obama and new media producer Christian Grantham with no apparent theme.
Mashup: A video of clips from different news station's news coverage. A video of clips of different horse ranches. A video of clips of past presidential campaigns. A video of clips of various rock videos.