The bright areas are too bright for your currently set exposure and are equivalent to "blown highlights" in still image mode. Sensors, just like film, have a finite dynamic range between the minimum and maximum illumination that can be recorded. To avoid the sensor overload that has occured in this scene exposure needs to be adjusted so that the highly illuminated points are not overloading the sensor HOWEVER this setting may cause the dark areas to be so dark that detail is lost.
If you cannot recompose the scene to avoid excessively bright areas then you will need to adjust the exposure level and what options are available to you depends upon the model you are using. Choosing a lower iso may allow better dynamic range, you may need to use exposure lock after letting the camera meter an area primarily containing the excessive illumination, dial in exposure compensation, etc. Look at the exposure section of your manual for details.
And pay particular attention to the warning in the manual about sensor damage in video mode when aimed at an intense light source because unlike typical still photography the sensor is exposed to the light source at a continuos duty cycle.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
