PHVideoRequestOptionsDeliveryMode.fastFormat
Photos provides whatever quality of video can be most quickly loaded.
Declaration
case fastFormatDiscussion
When the isNetworkAccessAllowed property is true, the fast option provides a version of the video asset suitable for streaming from iCloud over a low-quality connection—for example, an MP4 video with 360p resolution. If a higher-quality version is already cached on the device, Photos provides that video instead.