Unclear what you're asking.
What priority (or other resource treatment) video gets (as Mark notes) depends first whether the switch is enabled for QoS (for some you need to manually activate it) and the QoS configuration. The latter determines what traffic treatment video will be provided (if any). BTW, keep in mind, there are different kinds of video streams, and all do not need to be, or recommended to be, treated alike. Generally video that supports "real-time" interactive video is provided the best treatment for video. Also as Mark notes, VoIP voice bearer might be provided even better treatment (as might network control and network issues - not mentioned by Mark). Other video types, like streaming video, often are provided a lower or harsher treatment than real-time interactive video.
DSCP markings often are used to indicate how packets should be treated, but that's not a requirement, as traffic treatment might be determined by other attributes of the packet. BTW, when it comes to how traffic is marked, there's RFC 4594 and Cisco DSCP marking recommendations, which differ slightly.
QoS features, provided by switches, can vary quite a bit, and are often fewer than provided by "routers". Most Enterprise switches, though, provide some QoS support.
