With Sony A7S III, you can record your videos at a highest resolution of 3840 x 2160 at 120p, 60p, 50p,30p,25p,24p fps with bit rates up to 500 mbps and save in MPEG-4, XAVC S, XAVC HS, XAVC S-1, H.264 and H.265 formats. This means that Sony A7S III provides 4K (Ultra-HD) video. Except some rare 6K and 8K video recording cameras, 4K is the common standard in consumer video world.It is also a big step up from its predecessor which has a max video resolution of only. If you are thinking of upgrading your and shoot a lot of video, this is a big factor to consider in favor of A7S III.
A great advantage of Sony A7S III while shooting video at max resolution of 4K (UHD) is that there is no crop factor so you can use your lens with its actual focal length.
A7S III features a high speed mode where it captures videos at 240fps which helps to create slow motion videos. If you shoot a video at a frame rate of 240fps and play it back at 24fps, the video will be 10x slower and longer than normal.
A7S III has a built-in Stereo microphone and a Mono speaker. Sony A7S III also has a port for an external microphone and a headphone port for connecting external headphones which make Sony A7S III a very suitable camera high quality videography.
Sony A7S III also features an Digital Video Stabilization mode where videos are stabilized in-camera while you are shooting. Keep in mind that this effect may crop your videos a little bit and doesn't help stabilizing still images. This kind of video stabilization effect can be replicated by using some of the advanced video editing softwares in your PC.