Youtube Query String Arguments

These are the query string parameters (also called arguments) that get tagged at the end of a Youtube URL. They are the ampersands (“&”) and text at the end of a web address (URL). In the case of Youtube, this string of of code is the query string parameters and it adds functionality to what is presented. This is a comprehensive guide of Youtube’s query string arguments. We will be updating it as we find new query strings.

Query

Translation
&hl= hl stands for Host Language (thank you MapKi!) It is followed by “hl Parameter Values” which correspond to “Language/Locales” ex. en-US means English (United States and Canada).

It also can stand for hoc loco, which is Latin for “in this place” or hl stands for “human language”, but not in this case.
&video_id= Youtube video ID – used in conjunction with &get_video? to embed a Youtube video into another application. Not supported by Youtubes terms of service and may no longer work.
&t= Youtube video tag – used in conjunction with Youtube video ID.
&fmt= &fmt=6 is good quality, &fmt=18 is better, and &fmt=22 is the best. Video must originally be in high definition (HD) to work. May not work regardless as this feature is in beta and not available for all videos.
&rel= Rel stands for related. In relation to youtube, rel=1 means show related feeds and rel=0 means don’t.
&fs= Allows the fullscreen button to show up or not. 1 means it will show up, 0 means it is disabled.
&start=225 Starts the video 225 seconds into the video.
&end=230 Stops the video 230 seconds into the video.

I recommend this extensive post on Youtube plugins and tools for more information and for advanced users, check out the Youtube Reference Guide.