appview: pages/markup: add support for video

appview/pages/markup/markdown.go

···
 func visitNode(ctx *RenderContext, node *htmlparse.Node) {
 	switch node.Type {
 	case htmlparse.ElementNode:
-		if node.Data == "img" {
+		if node.Data == "img" || node.Data == "source" {
 			for i, attr := range node.Attr {
 				if attr.Key != "src" {
 					continue
···
 
 func (rctx *RenderContext) Sanitize(html string) string {
 	policy := bluemonday.UGCPolicy()
-	policy.AllowAttrs("align", "style").Globally()
+
+	// video
+	policy.AllowElements("video")
+	policy.AllowAttrs("controls").OnElements("video")
+	policy.AllowElements("source")
+	policy.AllowAttrs("src", "type").OnElements("source")
+
+	policy.AllowAttrs("align", "style", "width", "height").Globally()
 	policy.AllowStyles(
 		"margin",
 		"padding",

camo/src/mimetypes.json

···
   "image/x-rgb",
   "image/x-xbitmap",
   "image/x-xpixmap",
-  "image/x-xwindowdump"
+  "image/x-xwindowdump",
+  "video/mp4"
 ]