There can be several reasons for the difference between the amount of data uploaded and the storage space consumed by the uploaded data. One of the primary reasons is the encoding of original files to support universal playback. Encoding creates a copy of the uploaded file in a generalized codec.
Another reason is transcoding. Transcoding creates multiple lower-quality renditions of the video file that are suited for playback on lower bandwidth connections. Each of these renditions is a compressed copy of the source file. This ensures the media can be streamed at varying internet speeds and allows adaptive bitrate streaming.
Other possible reasons for the difference may include data compression, metadata, and other file optimization types that can reduce the overall size of the uploaded data. Additionally, the amount of storage space required may depend on the specific settings and configurations of the platform or system used to store the data.