Flash/ajax file upload to blobstore?

Is it possible to use some enhanced component to upload files to blobstore?

I'm playing with uploadify but facing problems to put it to work. I would like to be able to filter the kind of file before send it to blobstore, as well as the file size and maybe show some progress bar during the upload...

PS: For those who also subscribe the gae-j group, this is a reposti开发者_如何学编程ng, since nobody answered this question in the group...

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Check out Plupload, which does pretty much everything you are looking for, and also this post, which demonstrates how to implement Plupload using App Engine.