Sending a QT uncompressed file to Compressor and converting into H264 I have no way of knowing the size of the final file (file size: unknown) which leads me through lengthy and frustrating testings.
Is there a Compressor plugin or something that can tell me what the final file size is going to be? Or any other suggestion?
Thank you.

There's an Apple widget named VideoSpace made by Digital Heaven that is a calculator for final file size. There's also a few free helper apps and effects plug-ins for Final Cut Pro. Disksomnia is a nice one that keeps your HD's spinning when FCP is open.

I use Bitrate Pro (http://www.apple.com/downloads/macosx/video/bitratepro.html).