The Canvas Capture extension allows video to be captured from HTML canvas elements. Currently, video is only output in the webm container in the browser's choice of codec (typically VPX). To use, simply navigate to a page with an animated canvas element and click the extension's browser action (toolbar button). A list of canvases present on the page will be displayed with some details about each one. Click the capture button next to the canvas that should be captured. When finished, click the stop button and a link will be generated to download the resulting video file (the file is constructed using Blobs; no network access is required). Captured videos can be previewed before they are downloaded. By default, videos are remuxed using libwebm in WebAssembly to produce a more useful video file that is seekable and shows a duration and progress in video players. Canvas Capture produces video files of canvas elements using the MediaRecorder, MediaStream and Blob APIs.