To help the chef understand how a convection oven decreases the cooking time, the best source of media would be:
A video explaining how a convection oven increases the transfer of heat.
This option would provide a visual and auditory explanation of how convection ovens work, specifically detailing how the fan circulates hot air and creates a more even cooking environment, which can significantly reduce cooking times. The dynamic presentation of the video would likely enhance understanding compared to static materials like photos or lists.
The other options, while potentially useful, do not focus specifically on the mechanism of heat transfer and efficiency offered by convection ovens as directly as a video would.