Media Metadata API: Extract raw tags for audio/video.

chrome/common/extensions/api/media_galleries.idl

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Use the <code>chrome.mediaGalleries</code> API to access media files (audio,
 // images, video) from the user's local disks (with the user's consent).
 namespace mediaGalleries {
 
   [inline_doc] enum GetMediaFileSystemsInteractivity {
     // Do not act interactively.
@@ skipping 102 matching lines @@
     // Generic metadata tags.
     DOMString? album;
     DOMString? artist;
     DOMString? comment;
     DOMString? copyright;
     long? disc;
     DOMString? genre;
     DOMString? language;
     DOMString? title;
     long? track;
+
+    // A dictionary of all the metadata in the media file. This metadata is in
+    // string form, and neither the key nor value is normalized.
+    object rawTags;

[Lei Zhang, 2014/04/01 19:28:10]

Maybe there is a better type for this? The extensions folks may know.

[tommycli, 2014/04/01 19:29:01]

yoz: Is 'object' the right data type to use? I essentially a map<string, string>
with no pre-defined keys.

[Yoyo Zhou, 2014/04/01 21:39:40]

I'm not that familiar with IDL. Adding asargent.

[asargent_no_longer_on_chrome, 2014/04/02 20:03:54]

Yeah, if you don't know the set of possible keys up front, it is appropriate to
use 'object'.

If there are some keys that you do know in advance and want to explicitly call
those out in documentation, but leave room for future expansion, one thing you
might do is:

dictionary Tags {
  long? foo;
  DOMSTRING? bar;
  object? additionalTags;
};


A better way to leave room for future expansion in WebIDL, that I think our
parser unfortunately does not currently support, would be:

interface Tags {
  attribute? long foo;
  attribute? DOMString bar;
}


This specifies the foo and bar attributes as things that are known in the
interface, but does not preclude additional named properties by objects
implementing the Tags interface. If adding this support sounds like fun, I'd be
happy to review CL's! But if you want to avoid the yak shave, going with just
object or the dictionary-with-embedded-object approaches are fine. 

   };
 
   callback MediaMetadataCallback = void (MediaMetadata metadata);
 
   interface Functions {
     // Get the media galleries configured in this user agent. If none are
     // configured or available, the callback will receive an empty array.
     static void getMediaFileSystems(optional MediaFileSystemsDetails details,
                                     MediaFileSystemsCallback callback);
 
@@ skipping 34 matching lines @@
                             optional MediaMetadataOptions options,
                             MediaMetadataCallback callback);
   };
 
   interface Events {
     // The pending media scan has changed state. See details for more
     // information.
     static void onScanProgress(ScanProgressDetails details);
   };
 };