MYCOMETG3  Try nclc under settings window-extra options tab.

If you are in Europe and SD source(=PAL), would be nclc 516.

If you are in America and SD source(=NTSC), would be nclc 616.

If you are handling HD source, would be nclc 111.

Under Standard Video Compression Settings dialog, Preview image is not correct. Test by exact output.  
(Version 1.1.7)

STARHAWK79  Im mainly using SD in America so I tried the 6-1-6 atom and still have the issue. Im a bit at a loss as to where the problem is; x264 output on QTX is Dark, on VLC is even Darker, and on QT7 it looks pretty good!

Maybe these images can convey what I am seeing:

h.264 QTX vs x264 QTX: http://img.skitch.com/20091110-gnmnupa4249qrix9tkn7ukpcrc.jpg

h.264 QTX vs x264 VLC: http://img.skitch.com/20091110-fw7us894uje8js2br4batreeex.jpg

h.264 QTX vs x264 QTX 6-1-6:http://img.skitch.com/20091110-1d79sjwwqc95e1dy4hsnq39jeh.jpg

h.264 QT7 vs x264 QT7:http://img.skitch.com/20091110-jwtejgapcj52q86bssuc8isiy3.jpg

All images captured running Snow Leopard 10.6.2 with default Color LCD Display profile.  
(Version 1.1.7)

MYCOMETG3  I did some simple test using DV-NTSC.mov source file under both 10.5.8 and 10.6.2.

I used QuickTime Player 7. I can not reproduce your issue.

If you could, please upload short clip(~3 sec) and let me know via mail.  
(Version 1.1.7)

STARHAWK79  Sure! Can you provide me with your email address? I could not find it on your site.  
(Version 1.1.7)

MYCOMETG3  PLEASE READ README.rtf FIRST.

I get over 1000 spam mails a week. I had NEVER put my mail address on my site though!  
(Version 1.1.7)

STARHAWK79  Here you go. I'll just give you the links through here. Im not sure if this is the best test footage, just what I had in front of me first.

These were both encoded using iMovie '09 8.0.5 on MacOSX 10.6.2. The x264 file with x264 1.1.7 with default settings and h.264 file with built-in Quicktime h.264 with default settings.

x264 Encode Test-No nclc atom: http://dl.dropbox.com/u/277171/x264%20Encode%20Test%20-%20No%20nclc%20atom.mov

h.264 Encode Test (for comparison): http://dl.dropbox.com/u/277171/h264%20Encode%20Test.mov

I did not notice this difference until I upgraded to Snow Leopard.  
(Version 1.1.7)

STARHAWK79  What's funny is that I started viewing the x264 file I uploaded through my browsers. It looks fine in Safari and looks really dark in Firefox.  
(Version 1.1.7)

MYCOMETG3  Your samples are :

- apple h.264 has nclc 616 in mov.

- x264 sample does not have nclc atom.

Upload x264 with nclc 616 please.  
(Version 1.1.7)

STARHAWK79  Sure: http://dl.dropbox.com/u/277171/x264%20Encode%20Test%206-1-6.mov  
(Version 1.1.7)

STARHAWK79  Forget what I said earlier about the file looking good in Safari. My mistake. The video is dark in both Safari and Firefox, regardless of the 6-1-6 atom being included.  
(Version 1.1.7)

MYCOMETG3  Hmm... I understand what you see, but I can not find any cause.

- Is it able to upload source data (not exported but source data)?

- what version of imovie are you using?

mov file is desirable. I don't know iMovie is capable of exporting movie without transcode though...   
(Version 1.1.7)

STARHAWK79  Ok, I think I may have figured out what is going on, and it looks like it's not x264.

If I were to go to the x264 settings, I would notice that the preview window was much darker than the source file: http://img.skitch.com/20091113-exj43gmr26386griduc2abquxe.jpg

Switching to h.264 (or any other choice) showed a preview window much closer to the original source: http://img.skitch.com/20091113-ns842yu76qws2fskm1hxtkfay9.jpg

So, right now Im thinking the x264 file will be darker than the h.264. This IS true and what my original pictures above showed.

But in reality, what is happening is h.264 is actually producing video that is LIGHTER than the source! I was able to go through iMovie package files to find the source and compare: http://img.skitch.com/20091113-8wx6km4b2hasuiujrm3scw3qri.jpg

http://img.skitch.com/20091113-qnfp9tu3b1itmjaxyhjn56kbkp.jpg

What threw me off was the preview window. x264's preview window is darker than the source, but exports OK. h.264's preview window looks OK, but exports video that is lighter than the source.

Does that make sense? Thank you for looking over this with me, and for always keeping this Quicktime plugin up to date!  
(Version 1.1.7)