Tags are descriptive keywords you can add to your video to help people find your content. However, you can also add tags to change the appearance and format of your video on YouTube and on embedded players.

Examples of formatting tags

• yt:quality=high: Defaults to a high quality stream (available based on the size of the viewer’s player and the size of the browser window)
• yt:crop=16:9: Zooms in on the 16:9 area, removes windowboxing
• yt:stretch=16:9: Fixes anamorphic content by scaling to 16:9
• yt:stretch=4:3: Fixes 720x480 content that is the wrong aspect ratio by scaling to 4:3
• yt:crop=off: Deactivates cropping effects on the video and reestablishes cropped areas

How to add tags:

While you’re uploading, you'll see a “Tags” section below the upload progress bar where you can add your tags.

To add tags to an existing video, visit your Video Manager, then click the Edit button below the video for which you'd like to add formatting tags.

* Nguồn: Youtube