Writing XMP Thumbnail Metadata to AE Preset

Question

Hi guys.
I am working on a After Effects script to basically insert a gif as metadata into a fx preset file. If you open Adobe bridge and browse to the After effects text presets you will see that you can click on a preset and in the preview there is an animated GIF. So I am attempting to do this for custom presets.
Basically I think I need to read the contents of a GIF file as data, or text, then encode that as base64 and insert it into the metadata of the preset file.
I have a come across a couple of problems though:
1) I can't seem to read in the GIF file as data
     The code I am using is:
file = new File("C:\\test.gif");
file.open("r");
test = file.read();
alert(test);
And all I get returned is the first part of the data which is "GIF89aØ", It seems that when white space is encountered After Effects stops reading the data.
2) I have been testing some code to write thumbnail data to a preset file, but I have come across an issue here too.
if (ExternalObject.AdobeXMPScript == undefined) {
ExternalObject.AdobeXMPScript = new ExternalObject('lib:AdobeXMPScript');
xmpFile.closeFile(XMPConst.CLOSE_UPDATE_SAFELY);
file = new File("C:\\joshPreset.ffx");
xmpFile = new XMPFile(file.fsName, XMPConst.UNKNOWN, XMPConst.OPEN_FOR_UPDATE);
var xmp = xmpFile.getXMP();
xmp.appendArrayItem( "http://ns.adobe.com/xap/1.0/","Thumbnails",null, 0,XMPConst.ARRAY_IS_ALTERNATIVE );
This code works, it inserts a Thumbnails array into the metadata, which looks like this:
   <xmp:Thumbnails>
    <rdf:Alt>
    </rdf:Alt>
   </xmp:Thumbnails>
I then need to add other properties within the Thumbnails array like xapGImg:height and xapGImg:image
So from what I read in the documentation I need to add a Struct field?
I add these lines to my code:
XMPMeta.registerNamespace("http://ns.adobe.com/xap/1.0/g/img/", "xapGImg");
xmp.setStructField("xapGImg","Thumbnails","xapGImg:height", 0,null );
The first line is to register the name space. xapGImg is what I found in the after effects text preset file.
The second line is to add a struct field to the array. But I get an error whenever I run it with the second line. It says:
XMP Exception: Unregistered schema namespace URI
I have tried all different combinations of the namespace in the second line but just cannot get it to work!
If anyone can help that would be great!

Answer 1

Hi AthorNZ,
I can only give you some answers regarding question 2.
First of all you should be aware that XMPFiles does not offer smart handling of AE project files. Instead it uses so called "packet scanning" to work with the XMP within the file. This means that reading of XMP data works fairly well but updating it is rather limited. If no XMP is present in the file, it cannot be newly injected. If XMP is present, it can only be updated within the given space (i.e. padding) that already exists within the file. Otherwise an update is rejected.
Regarding the thumbnails: Your first snippet of code is correct. But for one you do not need to register the thumbnail related namespace as it is a pre-registered one. So you can use the constants from XMP_Const.h to work with those namespaces.
Secondly to set a struct field within the array you need to use the namespace URIs and not prefixes. Again you can use constants already defined:
xmp.setStructField( kXMP_NS_XMP, "Thumbnails", kXMP_NS_XMP_Image, "height", <your value> );
You got the exception because XMPCore tried to interpret your prefixes as URIs which were not registered, of course.
Kind regards
Jörg
Adobe XMP