Newbie question about chaining deffereds

Hello,

I need to download a videofile, a thumbnail to it, process that 
videofile, and after the processing is finished, process the thumbnail 
with the result of processing the video.

I do this, but it the logic (or the order) is wrong, so it does not 
work, it freezes after processing the video, while it downloads both of 
the files:

url = 'http://..../video.flv'
filename = 'video.flv'
video_deffered = downloadPage(url, filename)
video_deffered.addCallback(process_video, filename) => process_video 
returns video_id

url = 'http://..../thumbnail.jpg'
filename = 'thumbnail.jpg'
image_deffered = downloadPage(url, filename)

image_deffered.chainDeffered(video_deffered)
image_deffered.addCallback(process_image, filename) =< video_id needed here

What should I change for it to work?
And also I need to make process_video and process_image work in threads, 
but I can't figure out how to solve this problem first.