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How YouTube Determines What Video Quality To Play

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YouTube has two different players that it uses to play videos. One player is made with HTML5, while the other is made with Flash. They look very similar, but the video quality they default to is very different.

For Chrome and newer Internet Explorer browsers, YouTube shows the HTML5 video player on their site. With this player, the video quality is based on the video player size and connection speed only. YouTube no longer has a set default video quality of 360p; it's now dynamic and based on each user as they're viewing the video. The video quality can also change during playback if the user's connection improves or degrades (1). The user can still choose the quality level they want from the settings menu in the video.

For the Firefox browser, YouTube still shows the original Flash video player (version 3). This defaults to 360p in most cases, but can be controlled with the query string (if you're linking to or embedding the video).


Player Size And Video Quality


For the HTML5 player, these are the video qualities that will be played depending on the video player width:

Embed WidthDefault Video Quality
725 px or less360p
726 to 1088 px480p
1089 to 1632 px720p
1633 px or higher1080p

Again, the user's connection speed and settings can override this. For example, the user may choose a higher resolution from the settings menu.

When viewing videos on youtube.com on a desktop browser, the video player size will be either 640, 854, or 1280, depending on the browser width and whether it's in default view or "theater" view (wide).
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Comments (2)

Mouadh Hsoumi   Oct 27, 2016
no one care about safari , it sucks and it will always suck
Matt Carrell   Jul 15, 2016
And what about Safari? OH well, we can guess since it was the first browser to adopt and push HTML5, the answer is Safari's default player is HTML5, right?
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