[Cjmovie]

The exact answer can be found in Team Update #5:

Every time the Driver Station and ROBOT communicate, a 1024-byte packet is sent
between them. 40 bytes are reserved for use by the Field Management System. The
remaining 984 bytes are available for teams to put in any of the user data that they
want. The team can choose to send whatever they want in those 984 bytes.

Video is typically transmitted from the ROBOT by using the software ports
specifically set up to support video throughput. This year, the Field Management
System will not pass data sent through that port during a match (to ensure adequate
system performance during competition events, until the new system is better
characterized in actual competition settings). If a team really wants to transmit
images from the camera back to the Driver Station during a competition, they can
decompose the video frame and pass it as user data in the available 984 bytes per
packet. However, the resulting throughput of the video will likely result in a frame rate
so slow that it is not particularly useful.

Emphasis is my own.