Как youtube воспроизводит видео?

Плохо всматриваетесь

Dias Oral, Судя по всему, вам подойдет поколупать исходники youtube-dl

https://github.com/rg3/youtube-dl/

потоковое воспроизведение видео,
когда каждая минута свой кусочек

Request URL:https://r8---sn-hxb54vo-gv8l.googlevideo.com/video...
Request Method:GET
Status Code:200
Remote Address:37.29.1.147:443
Referrer Policy:origin-when-cross-origin
Response Headers
accept-ranges:bytes
access-control-allow-credentials:true
access-control-allow-origin:https://www.youtube.com
access-control-expose-headers:Client-Protocol, Content-Length, Content-Type, X-Bandwidth-Est, X-Bandwidth-Est2, X-Bandwidth-Est3, X-Bandwidth-App-Limited, X-Bandwidth-Est-App-Limited, X-Bandwidth-Est-Comp, X-Bandwidth-Avg, X-Head-Time-Sec, X-Head-Seqnum, X-Response-Itag, X-Restrict-Formats-Hint, X-Sequence-Num, X-Segment-Lmt, X-Walltime-Ms
alt-svc:hq=":443"; ma=2592000; quic=51303431; quic=51303339; quic=51303338; quic=51303337; quic=51303335,quic=":443"; ma=2592000; v="41,39,38,37,35"
cache-control:private, max-age=21219
client-protocol:quic
content-length:1619704
content-type:video/webm
date:Fri, 16 Feb 2018 16:22:25 GMT
expires:Fri, 16 Feb 2018 16:22:25 GMT
last-modified:Thu, 15 Feb 2018 13:38:03 GMT
server:gvs 1.0
status:200
timing-allow-origin:https://www.youtube.com
x-content-type-options:nosniff
x-restrict-formats-hint:None

А можно ли скачать видео напрямую?

Video Downloader Pro.