It's being output from the engine in the
YUYV-DXT compressed format, but that compression is actually a very light one - both because it takes place on GPU, and it's main purpose is to lower the requirement IO throughput below the usual sustainable disk write rates. The compression reduces the size to 1/3.
For example, a yog video of length 1:50 takes around 3GB. A 2-pass hq h264 converted video that I took for comparison here takes around 55MB, while a video in MJPEG format that we are using for further editing takes around 382MB in this particular case.