flv videos not encoding

[pgvideo]

I downloaded a video off of YouTube and uploaded it to my library. It never got past 3% during the encoding process then failed. Tried numerous times over the past 24hrs without NO success.
I finally found another place where I was able to download the same video from YouTube but in .mp4. Was a little confused why this particular program downloaded this video in mp4 but none the less was able to upload it to my library. This time it encoded with success!

Unfortunately the .flv download was 9.62mb while the .mp4 download was 17.9
That's almost twice the size for a short little 4min video.

I NEED to know what's going on with the Encoding...

Thanks,
Danielle