PHVideoRequestOptionsDeliveryMode.mediumQualityFormat
Photos provides a video of moderate quality unless a higher quality version is locally cached.
Declaration
case mediumQualityFormatDiscussion
When the isNetworkAccessAllowed property is true, the medium quality option provides a version of the video asset that is suitable for streaming from iCloud and displaying on a device—for example, an MP4 video with 720p resolution. If a higher-quality version is already cached on the device, Photos provides that video instead.