diff --git a/includes/amp-helper-functions.php b/includes/amp-helper-functions.php
index f3a4d9896a9..4939f0417f8 100644
--- a/includes/amp-helper-functions.php
+++ b/includes/amp-helper-functions.php
@@ -293,7 +293,6 @@ function amp_get_content_sanitizers( $post = null ) {
 	 */
 	return apply_filters( 'amp_content_sanitizers',
 		array(
-			'AMP_Style_Sanitizer'             => array(),
 			'AMP_Img_Sanitizer'               => array(),
 			'AMP_Form_Sanitizer'              => array(),
 			'AMP_Comments_Sanitizer'          => array(),
@@ -303,6 +302,7 @@ function amp_get_content_sanitizers( $post = null ) {
 			'AMP_Iframe_Sanitizer'            => array(
 				'add_placeholder' => true,
 			),
+			'AMP_Style_Sanitizer'             => array(),
 			'AMP_Tag_And_Attribute_Sanitizer' => array(), // Note: This whitelist sanitizer must come at the end to clean up any remaining issues the other sanitizers didn't catch.
 		),
 		$post
diff --git a/includes/class-amp-autoloader.php b/includes/class-amp-autoloader.php
index 5c51b42af09..f9dfb3dc175 100644
--- a/includes/class-amp-autoloader.php
+++ b/includes/class-amp-autoloader.php
@@ -88,8 +88,9 @@ class AMP_Autoloader {
 		'AMP_WP_Utils'                                => 'includes/utils/class-amp-wp-utils',
 		'AMP_Widget_Archives'                         => 'includes/widgets/class-amp-widget-archives',
 		'AMP_Widget_Categories'                       => 'includes/widgets/class-amp-widget-categories',
-		'AMP_Widget_Media_Gallery'                    => 'includes/widgets/class-amp-widget-media-gallery',
+		'AMP_Widget_Media_Video'                      => 'includes/widgets/class-amp-widget-media-video',
 		'AMP_Widget_Recent_Comments'                  => 'includes/widgets/class-amp-widget-recent-comments',
+		'AMP_Widget_Text'                             => 'includes/widgets/class-amp-widget-text',
 		'WPCOM_AMP_Polldaddy_Embed'                   => 'wpcom/class-amp-polldaddy-embed',
 		'AMP_Test_Stub_Sanitizer'                     => 'tests/stubs',
 		'AMP_Test_World_Sanitizer'                    => 'tests/stubs',
diff --git a/includes/embeds/class-amp-gallery-embed.php b/includes/embeds/class-amp-gallery-embed.php
index 1261d38747b..46d44fd6951 100644
--- a/includes/embeds/class-amp-gallery-embed.php
+++ b/includes/embeds/class-amp-gallery-embed.php
@@ -16,15 +16,13 @@ class AMP_Gallery_Embed_Handler extends AMP_Base_Embed_Handler {
 	 * Register embed.
 	 */
 	public function register_embed() {
-		add_shortcode( 'gallery', array( $this, 'shortcode' ) );
+		add_filter( 'post_gallery', array( $this, 'override_gallery' ), 10, 2 );
 	}
 
 	/**
 	 * Unregister embed.
 	 */
-	public function unregister_embed() {
-		remove_shortcode( 'gallery' );
-	}
+	public function unregister_embed() {}
 
 	/**
 	 * Shortcode handler.
@@ -120,6 +118,20 @@ public function shortcode( $attr ) {
 		) );
 	}
 
+	/**
+	 * Override the output of gallery_shortcode().
+	 *
+	 * The 'Gallery' widget also uses this function.
+	 * This ensures that it outputs an <amp-carousel>.
+	 *
+	 * @param string $html Markup to filter, possibly ''.
+	 * @param array  $attributes Shortcode attributes.
+	 * @return string $html Markup for the gallery.
+	 */
+	public function override_gallery( $html, $attributes ) {
+		return $this->shortcode( $attributes );
+	}
+
 	/**
 	 * Render.
 	 *
diff --git a/includes/embeds/class-amp-vimeo-embed.php b/includes/embeds/class-amp-vimeo-embed.php
index 6e0754b227e..6b334ce6441 100644
--- a/includes/embeds/class-amp-vimeo-embed.php
+++ b/includes/embeds/class-amp-vimeo-embed.php
@@ -32,6 +32,7 @@ function __construct( $args = array() ) {
 	function register_embed() {
 		wp_embed_register_handler( 'amp-vimeo', self::URL_PATTERN, array( $this, 'oembed' ), -1 );
 		add_shortcode( 'vimeo', array( $this, 'shortcode' ) );
+		add_filter( 'wp_video_shortcode_override', array( $this, 'video_override' ), 10, 2 );
 	}
 
 	public function unregister_embed() {
@@ -107,4 +108,27 @@ private function get_video_id_from_url( $url ) {
 
 		return $video_id;
 	}
+
+	/**
+	 * Override the output of Vimeo videos.
+	 *
+	 * This overrides the value in wp_video_shortcode().
+	 * The pattern matching is copied from WP_Widget_Media_Video::render().
+	 *
+	 * @param string $html Empty variable to be replaced with shortcode markup.
+	 * @param array  $attr The shortcode attributes.
+	 * @return string|null $markup The markup to output.
+	 */
+	public function video_override( $html, $attr ) {
+		if ( ! isset( $attr['src'] ) ) {
+			return $html;
+		}
+		$src           = $attr['src'];
+		$vimeo_pattern = '#^https?://(.+\.)?vimeo\.com/.*#';
+		if ( 1 === preg_match( $vimeo_pattern, $src ) ) {
+			return $this->shortcode( array( $src ) );
+		}
+		return $html;
+	}
+
 }
diff --git a/includes/embeds/class-amp-youtube-embed.php b/includes/embeds/class-amp-youtube-embed.php
index be1b3217a5a..a019a6a6334 100644
--- a/includes/embeds/class-amp-youtube-embed.php
+++ b/includes/embeds/class-amp-youtube-embed.php
@@ -24,7 +24,7 @@ function __construct( $args = array() ) {
 
 		if ( isset( $this->args['content_max_width'] ) ) {
 			$max_width = $this->args['content_max_width'];
-			$this->args['width'] = $max_width;
+			$this->args['width']  = $max_width;
 			$this->args['height'] = round( $max_width * self::RATIO );
 		}
 	}
@@ -32,6 +32,7 @@ function __construct( $args = array() ) {
 	function register_embed() {
 		wp_embed_register_handler( 'amp-youtube', self::URL_PATTERN, array( $this, 'oembed' ), -1 );
 		add_shortcode( 'youtube', array( $this, 'shortcode' ) );
+		add_filter( 'wp_video_shortcode_override', array( $this, 'video_override' ), 10, 2 );
 	}
 
 	public function unregister_embed() {
@@ -125,4 +126,27 @@ private function sanitize_v_arg( $value ) {
 
 		return $value;
 	}
+
+	/**
+	 * Override the output of YouTube videos.
+	 *
+	 * This overrides the value in wp_video_shortcode().
+	 * The pattern matching is copied from WP_Widget_Media_Video::render().
+	 *
+	 * @param string $html Empty variable to be replaced with shortcode markup.
+	 * @param array  $attr The shortcode attributes.
+	 * @return string|null $markup The markup to output.
+	 */
+	public function video_override( $html, $attr ) {
+		if ( ! isset( $attr['src'] ) ) {
+			return $html;
+		}
+		$src             = $attr['src'];
+		$youtube_pattern = '#^https?://(?:www\.)?(?:youtube\.com/watch|youtu\.be/)#';
+		if ( 1 === preg_match( $youtube_pattern, $src ) ) {
+			return $this->shortcode( array( $src ) );
+		}
+		return $html;
+	}
+
 }
diff --git a/includes/sanitizers/class-amp-video-sanitizer.php b/includes/sanitizers/class-amp-video-sanitizer.php
index 804a2a6ceb8..87bf0df6924 100644
--- a/includes/sanitizers/class-amp-video-sanitizer.php
+++ b/includes/sanitizers/class-amp-video-sanitizer.php
@@ -124,7 +124,8 @@ public function sanitize() {
 	 * @return array Returns HTML attributes; removes any not specifically declared above from input.
 	 */
 	private function filter_attributes( $attributes ) {
-		$out = array();
+		$out          = array();
+		$out['style'] = 'max-width:100%'; // Note that this will get moved to amp-custom style by AMP_Style_Sanitizer.
 
 		foreach ( $attributes as $name => $value ) {
 			switch ( $name ) {
diff --git a/includes/widgets/class-amp-widget-media-gallery.php b/includes/widgets/class-amp-widget-media-gallery.php
deleted file mode 100644
index e836025a986..00000000000
--- a/includes/widgets/class-amp-widget-media-gallery.php
+++ /dev/null
@@ -1,67 +0,0 @@
-<?php
-/**
- * Class AMP_Widget_Media_Gallery
- *
- * @since 0.7.0
- * @package AMP
- */
-
-if ( class_exists( 'WP_Widget_Media_Gallery' ) ) {
-	/**
-	 * Class AMP_Widget_Media_Gallery
-	 *
-	 * @todo This subclass can eventually be eliminated once #25435 is merged and the WP_Widget_Media_Gallery::render_media() does do_single_shortcode( 'gallery', $instance ).
-	 * @link https://core.trac.wordpress.org/ticket/25435
-	 * @since 0.7.0
-	 * @package AMP
-	 */
-	class AMP_Widget_Media_Gallery extends WP_Widget_Media_Gallery {
-
-		/**
-		 * Renders the markup of the widget.
-		 *
-		 * Mainly copied from WP_Widget_Media_Gallery::render_media().
-		 * But instead of calling shortcode_gallery(), it calls do_shortcode().
-		 *
-		 * @since 0.7.0
-		 *
-		 * @param array $instance Data for widget.
-		 * @return void
-		 */
-		public function render_media( $instance ) {
-			if ( ! is_amp_endpoint() ) {
-				parent::render_media( $instance );
-				return;
-			}
-
-			$instance       = array_merge( wp_list_pluck( $this->get_instance_schema(), 'default' ), $instance );
-			$shortcode_atts = array_merge(
-				$instance,
-				array(
-					'link' => $instance['link_type'],
-				)
-			);
-
-			if ( isset( $instance['orderby_random'] ) && ( true === $instance['orderby_random'] ) ) {
-				$shortcode_atts['orderby'] = 'rand';
-			}
-
-			/*
-			 * The following calls do_shortcode() in case another plugin overrides the gallery shortcode.
-			 * The AMP_Gallery_Embed_Handler in the plugin is doing this itself, but other plugins may
-			 * do it as well, so this ensures that a plugin has the option to override the gallery behavior
-			 * via registering a different gallery shortcode handler. The shortcode serialization can be
-			 * eliminated once WP Trac #25435 is merged and the Gallery widget uses the proposed do_single_shortcode().
-			 */
-			$shortcode_atts_str = '';
-			if ( is_array( $shortcode_atts['ids'] ) ) {
-				$shortcode_atts['ids'] = join( ',', $shortcode_atts['ids'] );
-			}
-			foreach ( $shortcode_atts as $key => $value ) {
-				$shortcode_atts_str .= sprintf( ' %s="%s"', $key, esc_attr( $value ) );
-			}
-			echo do_shortcode( "[gallery $shortcode_atts_str]" ); // WPCS: XSS ok.
-		}
-
-	}
-}
diff --git a/includes/widgets/class-amp-widget-media-video.php b/includes/widgets/class-amp-widget-media-video.php
new file mode 100644
index 00000000000..1bcdfad5fc3
--- /dev/null
+++ b/includes/widgets/class-amp-widget-media-video.php
@@ -0,0 +1,33 @@
+<?php
+/**
+ * Class AMP_Widget_Media_Video
+ *
+ * @since 0.7.0
+ * @package AMP
+ */
+
+if ( class_exists( 'WP_Widget_Media_Video' ) ) {
+	/**
+	 * Class AMP_Widget_Media_Video
+	 *
+	 * @since 0.7.0
+	 * @package AMP
+	 */
+	class AMP_Widget_Media_Video extends WP_Widget_Media_Video {
+
+		/**
+		 * Overrides the parent callback that strips width and height values.
+		 *
+		 * @param string $html Video shortcode HTML output.
+		 * @return string HTML Output.
+		 */
+		public function inject_video_max_width_style( $html ) {
+			if ( is_amp_endpoint() ) {
+				return $html;
+			}
+			return parent::inject_video_max_width_style( $html );
+		}
+
+	}
+
+}
diff --git a/includes/widgets/class-amp-widget-text.php b/includes/widgets/class-amp-widget-text.php
new file mode 100644
index 00000000000..6af7df11735
--- /dev/null
+++ b/includes/widgets/class-amp-widget-text.php
@@ -0,0 +1,33 @@
+<?php
+/**
+ * Class AMP_Widget_Text
+ *
+ * @since 0.7.0
+ * @package AMP
+ */
+
+if ( class_exists( 'WP_Widget_Text' ) ) {
+	/**
+	 * Class AMP_Widget_Text
+	 *
+	 * @since 0.7.0
+	 * @package AMP
+	 */
+	class AMP_Widget_Text extends WP_Widget_Text {
+
+		/**
+		 * Overrides the parent callback that strips width and height attributes.
+		 *
+		 * @param array $matches The matches returned from preg_replace_callback().
+		 * @return string $html The markup, unaltered.
+		 */
+		public function inject_video_max_width_style( $matches ) {
+			if ( is_amp_endpoint() ) {
+				return $matches[0];
+			}
+			return parent::inject_video_max_width_style( $matches );
+		}
+
+	}
+
+}
diff --git a/tests/test-amp-video-sanitizer.php b/tests/test-amp-video-sanitizer.php
index 140b3584025..f08f194db9e 100644
--- a/tests/test-amp-video-sanitizer.php
+++ b/tests/test-amp-video-sanitizer.php
@@ -10,42 +10,42 @@ public function get_data() {
 
 			'simple_video' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4"></video>',
-				'<amp-video width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'video_without_dimensions' => array(
 				'<video src="https://example.com/file.mp4"></video>',
-				'<amp-video src="https://example.com/file.mp4" height="400" layout="fixed-height"></amp-video>',
+				'<amp-video style="max-width:100%" src="https://example.com/file.mp4" height="400" layout="fixed-height"></amp-video>',
 			),
 
 			'autoplay_attribute' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" autoplay></video>',
-				'<amp-video width="300" height="300" src="https://example.com/video.mp4" autoplay="" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" autoplay="" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'autoplay_attribute__false' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" autoplay="false"></video>',
-				'<amp-video width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'video_with_whitelisted_attributes__enabled' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" controls loop="true" muted="muted"></video>',
-				'<amp-video width="300" height="300" src="https://example.com/video.mp4" controls="" loop="" muted="" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" controls="" loop="" muted="" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'video_with_whitelisted_attributes__disabled' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" controls="false" loop="false" muted="false"></video>',
-				'<amp-video width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'video_with_blacklisted_attribute' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" style="border-color: red;"></video>',
-				'<amp-video width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'video_with_sizes_attribute_is_overridden' => array(
 				'<video width="300" height="200" src="https://example.com/file.mp4" sizes="(min-width: 100px) 200px, 90vw"></video>',
-				'<amp-video width="300" height="200" src="https://example.com/file.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="200" src="https://example.com/file.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'video_with_children' => array(
@@ -53,7 +53,7 @@ public function get_data() {
 	<source src="https://example.com/video.mp4" type="video/mp4">
 	<source src="https://example.com/video.ogv" type="video/ogg">
 </video>',
-				'<amp-video width="480" height="300" poster="https://example.com/video-image.gif" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"><source src="https://example.com/video.mp4" type="video/mp4"><source src="https://example.com/video.ogv" type="video/ogg"></amp-video>',
+				'<amp-video style="max-width:100%" width="480" height="300" poster="https://example.com/video-image.gif" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"><source src="https://example.com/video.mp4" type="video/mp4"><source src="https://example.com/video.ogv" type="video/ogg"></amp-video>',
 			),
 
 			'multiple_same_video' => array(
@@ -61,19 +61,19 @@ public function get_data() {
 <video src="https://example.com/video.mp4" width="480" height="300"></video>
 <video src="https://example.com/video.mp4" width="480" height="300"></video>
 <video src="https://example.com/video.mp4" width="480" height="300"></video>',
-				'<amp-video src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'multiple_different_videos' => array(
 				'<video src="https://example.com/video1.mp4" width="480" height="300"></video>
 <video src="https://example.com/video2.ogv" width="300" height="480"></video>
 <video src="https://example.com/video3.webm" height="100" width="200"></video>',
-				'<amp-video src="https://example.com/video1.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video src="https://example.com/video2.ogv" width="300" height="480" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video src="https://example.com/video3.webm" height="100" width="200" sizes="(min-width: 200px) 200px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" src="https://example.com/video1.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video2.ogv" width="300" height="480" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video3.webm" height="100" width="200" sizes="(min-width: 200px) 200px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 
 			'https_not_required' => array(
 				'<video width="300" height="300" src="http://example.com/video.mp4"></video>',
-				'<amp-video width="300" height="300" src="http://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video style="max-width:100%" width="300" height="300" src="http://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
 			),
 		);
 	}
diff --git a/tests/test-class-amp-vimeo-embed-handler.php b/tests/test-class-amp-vimeo-embed-handler.php
new file mode 100644
index 00000000000..15e14b1f37f
--- /dev/null
+++ b/tests/test-class-amp-vimeo-embed-handler.php
@@ -0,0 +1,69 @@
+<?php
+/**
+ * Tests for AMP_Vimeo_Embed_Handler.
+ *
+ * @package AMP
+ * @since 0.7
+ */
+
+/**
+ * Tests for AMP_Vimeo_Embed_Handler.
+ *
+ * @covers AMP_Vimeo_Embed_Handler
+ */
+class Test_AMP_Vimeo_Embed_Handler extends WP_UnitTestCase {
+
+	/**
+	 * An instance of this embed handler.
+	 *
+	 * @var AMP_Vimeo_Embed_Handler.
+	 */
+	public $handler;
+
+	/**
+	 * Set up each test.
+	 */
+	public function setUp() {
+		parent::setUp();
+		$this->handler = new AMP_Vimeo_Embed_Handler();
+	}
+
+	/**
+	 * Test video_override().
+	 *
+	 * @covers AMP_Vimeo_Embed_Handler::video_override()
+	 */
+	public function test_video_override() {
+		remove_all_filters( 'wp_video_shortcode_override' );
+		$this->handler->register_embed();
+		$youtube_id   = 'XOY3ZUO6P0k';
+		$youtube_src  = 'https://youtu.be/' . $youtube_id;
+		$attr_youtube = array(
+			'src' => $youtube_src,
+		);
+
+		$youtube_shortcode = $this->handler->video_override( '', $attr_youtube );
+		$this->assertEquals( '', $youtube_shortcode );
+
+		$vimeo_id        = '64086087';
+		$vimeo_src       = 'https://vimeo.com/' . $vimeo_id;
+		$attr_vimeo      = array(
+			'src' => $vimeo_src,
+		);
+		$yimeo_shortcode = $this->handler->video_override( '', $attr_vimeo );
+		$this->assertContains( '<amp-vimeo', $yimeo_shortcode );
+		$this->assertContains( $vimeo_id, $yimeo_shortcode );
+
+		$daily_motion_id        = 'x6bacgf';
+		$daily_motion_src       = 'http://www.dailymotion.com/video/' . $daily_motion_id;
+		$attr_daily_motion      = array(
+			'src' => $daily_motion_src,
+		);
+		$daily_motion_shortcode = $this->handler->video_override( '', $attr_daily_motion );
+		$this->assertEquals( '', $daily_motion_shortcode );
+		$no_attributes = $this->handler->video_override( '', array() );
+		$this->assertEquals( '', $no_attributes );
+		remove_all_filters( 'wp_video_shortcode_override' );
+	}
+
+}
diff --git a/tests/test-class-amp-widget-media-gallery.php b/tests/test-class-amp-widget-media-gallery.php
deleted file mode 100644
index 281dd205adb..00000000000
--- a/tests/test-class-amp-widget-media-gallery.php
+++ /dev/null
@@ -1,77 +0,0 @@
-<?php
-/**
- * Tests for class AMP_Widget_Media_Gallery.
- *
- * @package AMP
- */
-
-/**
- * Tests for class AMP_Widget_Media_Gallery.
- *
- * @package AMP
- */
-class Test_AMP_Widget_Media_Gallery extends WP_UnitTestCase {
-
-	/**
-	 * Instance of the widget.
-	 *
-	 * @var object
-	 */
-	public $instance;
-
-	/**
-	 * Setup.
-	 *
-	 * @inheritdoc
-	 */
-	public function setUp() {
-		if ( ! class_exists( 'AMP_Widget_Media_Gallery' ) ) {
-			$this->markTestSkipped( 'This WordPress version does not have a Gallery widget.' );
-		}
-		parent::setUp();
-		AMP_Theme_Support::register_widgets();
-		$this->instance = new AMP_Widget_Media_Gallery();
-	}
-
-	/**
-	 * Test render_media().
-	 *
-	 * @see AMP_Widget_Media_Gallery::widget().
-	 */
-	public function test_render_media() {
-		$first_test_image = '/tmp/test-image.jpg';
-		copy( DIR_TESTDATA . '/images/test-image.jpg', $first_test_image );
-		$first_attachment_id = self::factory()->attachment->create_object( array(
-			'file'           => $first_test_image,
-			'post_parent'    => 0,
-			'post_mime_type' => 'image/jpeg',
-			'post_title'     => 'Test Image',
-		) );
-		wp_update_attachment_metadata( $first_attachment_id, wp_generate_attachment_metadata( $first_attachment_id, $first_test_image ) );
-		$ids[] = $first_attachment_id;
-
-		$second_test_image = '/tmp/test-image.jpg';
-		copy( DIR_TESTDATA . '/images/test-image.jpg', $second_test_image );
-		$second_attachment_id = self::factory()->attachment->create_object( array(
-			'file'           => $second_test_image,
-			'post_parent'    => 0,
-			'post_mime_type' => 'image/jpeg',
-			'post_title'     => 'Test Image',
-		) );
-		wp_update_attachment_metadata( $second_attachment_id, wp_generate_attachment_metadata( $second_attachment_id, $second_test_image ) );
-		$ids[]    = $second_attachment_id;
-		$instance = array(
-			'title' => 'Test Gallery Widget',
-			'ids'   => $ids,
-		);
-
-		ob_start();
-		$this->instance->render_media( $instance );
-		$output = ob_get_clean();
-
-		$this->assertContains( 'amp-carousel', $output );
-		$this->assertContains( $first_test_image, $output );
-		$this->assertContains( $second_test_image, $output );
-	}
-
-}
diff --git a/tests/test-class-amp-widget-media-video.php b/tests/test-class-amp-widget-media-video.php
new file mode 100644
index 00000000000..d93556d85ab
--- /dev/null
+++ b/tests/test-class-amp-widget-media-video.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * Tests for class AMP_Widget_Media_Video.
+ *
+ * @since 0.7.0
+ * @package AMP
+ */
+
+/**
+ * Tests for class AMP_Widget_Media_Video.
+ *
+ * @since 0.7.0
+ * @package AMP
+ */
+class Test_AMP_Widget_Media_Video extends WP_UnitTestCase {
+
+	/**
+	 * Instance of the widget.
+	 *
+	 * @var object.
+	 */
+	public $widget;
+
+	/**
+	 * Setup.
+	 *
+	 * @inheritdoc
+	 */
+	public function setUp() {
+		$class = 'AMP_Widget_Media_Video';
+		if ( ! class_exists( $class ) ) {
+			$this->markTestSkipped( 'This version of WordPress does not have the Video widget, so this test does not apply.' );
+		}
+		parent::setUp();
+		wp_maybe_load_widgets();
+		$this->widget = new $class();
+	}
+
+	/**
+	 * Test inject_video_max_width_style().
+	 *
+	 * @covers AMP_Widget_Media_Video::inject_video_max_width_style()
+	 */
+	public function test_inject_video_max_width_style() {
+		$video           = '<video src="http://example.com" height="100" width="200"></video>';
+		$video_no_height = '<video src="http://example.com" width="200"></video>';
+		$this->assertEquals( $video, $this->widget->inject_video_max_width_style( $video ) );
+		$this->assertEquals( $video_no_height, $this->widget->inject_video_max_width_style( $video_no_height ) );
+		$this->assertEquals( '', $this->widget->inject_video_max_width_style( '' ) );
+	}
+
+}
diff --git a/tests/test-class-amp-widget-text.php b/tests/test-class-amp-widget-text.php
new file mode 100644
index 00000000000..26d371d666f
--- /dev/null
+++ b/tests/test-class-amp-widget-text.php
@@ -0,0 +1,53 @@
+<?php
+/**
+ * Tests for class AMP_Widget_Text.
+ *
+ * @since 0.7.0
+ * @package AMP
+ */
+
+/**
+ * Tests for class AMP_Widget_Text.
+ *
+ * @since 0.7.0
+ * @package AMP
+ */
+class Test_AMP_Widget_Text extends WP_UnitTestCase {
+
+	/**
+	 * Instance of the widget.
+	 *
+	 * @var object.
+	 */
+	public $widget;
+
+	/**
+	 * Setup.
+	 *
+	 * @inheritdoc
+	 */
+	public function setUp() {
+		$class = 'AMP_Widget_Text';
+		if ( ! class_exists( $class ) ) {
+			$this->markTestSkipped( 'This version of WordPress does not have the Video widget, so this test does not apply.' );
+		}
+		parent::setUp();
+		wp_maybe_load_widgets();
+		$this->widget = new $class();
+	}
+
+	/**
+	 * Test inject_video_max_width_style().
+	 *
+	 * @covers AMP_Widget_Text::inject_video_max_width_style()
+	 */
+	public function test_inject_video_max_width_style() {
+		add_theme_support( 'amp' );
+		$video            = '<video src="http://example.com" height="100" width="200"></video>';
+		$video_only_width = '<video src="http://example.com/this-video" width="500">';
+		$this->assertEquals( $video, $this->widget->inject_video_max_width_style( array( $video ) ) );
+		$this->assertEquals( $video_only_width, $this->widget->inject_video_max_width_style( array( $video_only_width ) ) );
+		$this->assertEquals( '', $this->widget->inject_video_max_width_style( array( '' ) ) );
+	}
+
+}
diff --git a/tests/test-class-amp-youtube-embed-handler.php b/tests/test-class-amp-youtube-embed-handler.php
new file mode 100644
index 00000000000..eb82838f15c
--- /dev/null
+++ b/tests/test-class-amp-youtube-embed-handler.php
@@ -0,0 +1,69 @@
+<?php
+/**
+ * Tests for AMP_YouTube_Embed_Handler.
+ *
+ * @package AMP
+ * @since 0.7
+ */
+
+/**
+ * Tests for AMP_YouTube_Embed_Handler.
+ *
+ * @covers AMP_YouTube_Embed_Handler
+ */
+class Test_AMP_YouTube_Embed_Handler extends WP_UnitTestCase {
+
+	/**
+	 * An instance of this embed handler.
+	 *
+	 * @var AMP_YouTube_Embed_Handler.
+	 */
+	public $handler;
+
+	/**
+	 * Set up each test.
+	 */
+	public function setUp() {
+		parent::setUp();
+		$this->handler = new AMP_YouTube_Embed_Handler();
+	}
+
+	/**
+	 * Test video_override().
+	 *
+	 * @covers AMP_YouTube_Embed_Handler::video_override()
+	 */
+	public function test_video_override() {
+		remove_all_filters( 'wp_video_shortcode_override' );
+		$this->handler->register_embed();
+		$youtube_id   = 'XOY3ZUO6P0k';
+		$youtube_src  = 'https://youtu.be/' . $youtube_id;
+		$attr_youtube = array(
+			'src' => $youtube_src,
+		);
+
+		$youtube_shortcode = $this->handler->video_override( '', $attr_youtube );
+		$this->assertContains( '<amp-youtube', $youtube_shortcode );
+		$this->assertContains( $youtube_id, $youtube_shortcode );
+
+		$vimeo_id        = '64086087';
+		$vimeo_src       = 'https://vimeo.com/' . $vimeo_id;
+		$attr_vimeo      = array(
+			'src' => $vimeo_src,
+		);
+		$yimeo_shortcode = $this->handler->video_override( '', $attr_vimeo );
+		$this->assertEquals( '', $yimeo_shortcode );
+
+		$daily_motion_id        = 'x6bacgf';
+		$daily_motion_src       = 'http://www.dailymotion.com/video/' . $daily_motion_id;
+		$attr_daily_motion      = array(
+			'src' => $daily_motion_src,
+		);
+		$daily_motion_shortcode = $this->handler->video_override( '', $attr_daily_motion );
+		$this->assertEquals( '', $daily_motion_shortcode );
+		$no_attributes = $this->handler->video_override( '', array() );
+		$this->assertEquals( '', $no_attributes );
+		remove_all_filters( 'wp_video_shortcode_override' );
+	}
+
+}