Settings » Media Settings
Height, Images, Sizes, Thumbnail, Width
You can control image sizes, auto-embeds, and video player display formats under Settings > Media.

Image sizes allows you to change the maximum dimensions of images that are displayed on posts and pages. When setting a thumnail size, the image will be cropped and resized to the setting. Medium and large images will keep the dimension proportions, taking the maximum width and height into account.

Some of the previous settings for defaults have been removed. WordPress will now save the state of those settings from the last time you used them. For example, if you last inserted a full size image, that option will be set the next time you insert an image.
Auto-Embeds gives you the option to show a video player instead of just a plain text URL. You can also specify the maximum size for the player. We currently support auto-embeds from YouTube, Twitter, Vimeo, Viddler, Blip.tv, and Lytro, though videos from select other services can be embedded following the linked guides on the Videos page.

Video player gives you the option to display videos that are only in free software formats.

Video
Watch the “Changing your default media settings” video from WordPress.tv.
Last modified: February 7, 2012
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