I think some reposts, but something is strange.
My old download 'Gummy Smile' (best video ever) from 18.07.2015 has 76.566.192 Bytes, but the same video downloaded today has only 43.002.910 Bytes
/edit
Both downloads 1280x720, length 4:55
18.07.2015 1881 kbit/s
21.10.2016 1036 kbit/s
The quality decreased.
Changed the autor the file or is that an issue by youtube?