How To Replace Audio Without Re-Compressing Video???

[Rory Delaney]

Hey folks, i am trying to marry some dolby surround sound audio with a prores video. I added the 7 tracks of audio without a problem using Quicktime Pro but when i click Save As the file size goes from 130 gigs to like 110 gigs because it reduces the video dimensions from 1920 x 1080 to 960 x 540. Any clue what might be going wrong? I need to keep the dimensions at 1920 x 1080. Thanks!