459,212 bytes to be specific.
Don't be fooled by the quality settings, this is a 46p video.
Download the original file:
https://www.mediafire.com/file/n3718bq7tuzlxi9/story_of_undertale_%2528448_kb%2529.mp4/file
Download an even more compressed version that YouTube can't even process (329 KB) :
https://www.mediafire.com/file/q5h0tut70bmbfij/story_of_undertale_%2528329_kb%2529.mp4/file
GBA Video version just because I can:
https://www.mediafire.com/file/0yxtq3kg1ijeg9e/Story_of_Undertale.gba/file