After a sound mix, you will have an AIFF or WAV file containing the finished, mixed audio for your project. Matching this to your picture is called layback. There are several ways of doing this - any program that allows you to join an audio file to a picture file, confirm they are in sync, and re-export a single combined file, is usable. For this workflow, we will use Final Cut or another nonlinear editing program.
1.) Bring your mixed audio tracks into FCP. Duplicate your final sequence.
2.) Either delete or mute the audio from your final sequence. Replace it with the mixed tracks.
3.) Trim off the 2-beep and black slug from the head of the file - these are for syncing the mix and maintaining timing - they aren't necessary post-mix.
3.) Confirm sync at the beginning, middle, and end of the file.
IF YOU HAVE ONLINED YOUR SEQUENCE ALREADY TO 8-BIT UNCOMPRESSED, see 4a:
4a.) If sync is good, go to File-->Export-->Quicktime Movie. Leave at 'Current Settings.'
5a.) Save as Lastname, Firstname "Title" 8Bit FULL. Click OK.
IF YOU HAVE BEEN WORKING AT PRORES OR ANOTHER INTERMEDIATE CODEC, see 4b:
4b.) If sync is good, go to File-->Send To-->Compressor.
5b.) Right-click your job window to pull up the New Target with Setting option. Follow it through to Apple-->Formats-->Quicktime-->8-Bit Uncompressed.
5c.) Set a target (where it defaults to 'Source.') This is where your final file will be saved.
5d.) Save as Lastname, Firstname "Title" 8Bit FULL. Click Submit, click submit again.
*If you are laying mixed audio into your editing sequence, and exporting directly from there, select File-->Export-->Using Compressor, and apply your 8-bit Uncompressed setting there.
Layback Using Quicktime Pro
This workflow is contingent on your picture and sound files being equal duration.
1.) Open your picture file and your audio file separately in Quicktime Pro.
2.) With your audio file active, select all (Command-a), copy (Command-c).
3.) With your picture file active, go to Edit-->Add to Movie. This pastes your audio track into the picture file.
4.) Confirm sync.
5.) Go to File-->Export, choose Quicktime Movie at 8-Bit Uncompressed, etc.
Be aware that the "Save As..." option, while effectively combining the picture and sound, will create a file which is still dependent on the two original files being present. It will not be a completely self-contained picture-and-sound file. This is why Export is a better option, even if it is a longer wait.