YouTube/Technical details

This page documents some of the publicly known technical details of YouTube.

ID formats

In most places, IDs are expressed as base64 using the modified character set A-Za-z0-9-_.

Videos

Videos have a 64-bit ID. Because an 11-character base64 string is equivalent to 66 bit, the last character of a video ID can only take one of 16 values.

Video ID regex pattern: [A-Za-z0-9_-]{10}[048AEIMQUYcgkosw]

Channels

Channels have a 128-bit ID. In base64, this turns into a 22-character string where the last character can take 4 values.

Channel ID regex pattern: [A-Za-z0-9_-]{21}[AQgw]

(Note that this does not include the UC prefix used e.g. in /channel/ URLs. The channel ID appears without that prefix in several places, most notably some playlist IDs.)

Playlists

Over the years, there has been a large number of playlist types, many of which have since gone the way of the dodo. This section attempts to document them all.

In the table below, pattern is a regex with the additional syntax of <videoID> to indicate that the ID contains a video ID (and likewise for channel and playlist IDs).

Pattern	Purpose	Status	Examples	Notes
AL[A-Za-z0-9_-]+	Artist top tracks	Broken	[1]
AV[A-Za-z0-9_-]{32}	Artist on /artist?a=	Broken	[2]
BB[0-9]{8}	Billboard top 20	Unviewable, playnext broken, list param on watch page not functional but not removed by JS	[3]	The ID is a date in YYYYMMDD format and refers to a Saturday. Known values range from 20110910 to 20121201.
BLCM<channelID>		Broken
CL<videoID>		Semi-broken		In some cases, the playlist exists even though the video doesn't [4]; for these, the list parameter also works on the watch page. In other cases, the playlist doesn't exist but the video does [5].
EC([0-9A-F]{16}|[A-Za-z0-9_-]{32})	Courses	Unviewable, playnext and watch functional	[6]	IDs are also fully functional with PL: [7]
EL([A-Za-z0-9_-]{11}|[A-Za-z0-9_-]{22})	Movies & Shows	Broken	[8]	Some of the short IDs are video IDs, others are not. Even though the contents seem entirely unrelated (e.g. [9] vs [10]), it's highly unlikely that these are random collisions since there are quite a lot of them. The longer IDs do not appear to be channel IDs.
FL<channelID>	Favourites	Fully functional	[11]
HL[0-9]{10}		Unviewable, playnext broken	[12] [13]	Frequently associated with feature=mh_lolz. All WBM snapshots with this are either video pages or /embed/videoseries, and even the older snapshots provide no insight into this playlist type.
LE<channelID>[APU]	Live events	Broken	[14]	Frequently associated with feature=plcp
LL<channelID>	Likes	Dead		Made private in December 2019
LM
LM<channelID>		Broken
LP<videoID>	Auto-generated channels	Broken	[15] [16] [17]	It isn't always clear whether there is any relation between the two video IDs in the watch URL, e.g. [18] (vs [19]) or [20] (vs [21])
MC[0-9]{8}				Values appear to be dates
MCUS
ML[A-Za-z0-9_-]{32}		Broken		IDs do not appear to be PL ones
OLAK5uy_[klmn][A-Za-z0-9_-]{32}
PL[0-9A-F]{16}	Normal playlist (old)	Fully functional
PL[A-Za-z0-9_-]{32}	Normal playlist	Fully functional
PU<channelID>	Popular uploads	Unviewable, playnext and watch functional
RD<videoID>	Mix aka radio	Unviewable, playnext and watch functional
RD[0-4][0-9]<videoID>
RDAMVM[A-Za-z0-9_-]{22}	Artist mix?
RDAO[A-Za-z0-9_-]{22}	Artist mix
RDAMPL<playlistID>
RDCLAK5uy_[klmn][A-Za-z0-9_-]{32}
RDCMUC<channelID>	Channel mix
RDEM[A-Za-z0-9_-]{22}	Artist mix?
RDGMEM[A-Za-z0-9_-]{22}	Genre mix?
RDGMEM[A-Za-z0-9_-]{22}VM<videoID>	Genre mix?
RDHC<videoID>
RDKM[A-Za-z0-9_-]{22}
RDLV<videoID>
RDMM	My Mix			Tied to the account accessing YouTube
RDMM<videoID>
RDQM<videoID>
RDTMAK5uy_[klmn][A-Za-z0-9_-]{32}
SL
SL<videoID>		Broken
SP([0-9A-F]{16}|[A-Za-z0-9_-]{32})		Fully functional		Behaves exactly as the same ID with PL
TLGG[A-Za-z0-9_-]{22}	Temporary list			Produced by https://www.youtube.com/watch_videos?video_ids=<videoID>,<videoID>,... and https://www.youtube-nocookie.com/embed/<videoID>?playlist=<videoID>,<videoID>,...
TLPQ[A-Za-z0-9_-]{22}
UL<videoID>	User uploads	Watch functional		Only valid on watch pages. Triggers display of uploads by the same user as the watched video. The ID in the list parameter must be a valid video ID from any channel; in the past, any 11 characters were accepted, and even further in the past, a sole UL worked as well.
UU<channelID>	User/channel uploads	Fully functional	[22]
UUSH<channelID>	User shorts	Fully functional	[23]
WL	Watch Later			Tied to the account accessing YouTube

Further prefixes that are known or suspected to have existed but whose exact format isn't known yet: BP, MLCA, MQ, TT

URL formats

A large number of URL formats have been in use over the years, too many to be listed here. User:JustAnotherArchivist's youtube-extract script contain regex patterns for most of the ones that were at least somewhat common.

Domains

Domains actively serving content as of 2021:

• www.youtube.com (main site)
• m.youtube.com (mobile site)
• youtu.be (short URLs)
• www.youtube-nocookie.com (embeds only)
• music.youtube.com (YouTube Music)
• www.youtubekids.com (YouTube Kids)
• tv.youtube.com (YouTube TV)
• i.ytimg.com (static images like thumbnails; avatars are on subdomains of ggpht.com as they are shared between Google services)
• subdomains of googlevideo.com (video content)

A long time ago, there were YouTube domains under a number of ccTLDs. Nowadays, these all redirect to the main site: youtube.at, by, ca, co.uk, cz, de, dk, ee, es, fi, fr, gr, hr, hu, it, lt, lv, no, pl, pt, ro, rs, ru, se, si, sk.

In addition, there are some subdomains under youtube.com which redirect to the main site but add the gl parameter to the query string, which changes the interface language: br.youtube.com and likewise for es, it, jp, pl, ru, uk.