fcp.co has been a source that has helped me on many occasions, I thought I'd share this info to help anyone that had to trim source video for whatever reason.
Skip to the end for the summary without the full story.
I recently had to trim the start of some videos for a client, so they could pass it on to their editor (who wasn't using FCPX) with every thing synced up.
We had 3 sources, 2 cameras and a .mov file feed from a Powerpoint presentation. All the sources had a different starting time.
So I imported all the files into FCPX and made a Multicam clip, synced via the audio track on all the files.
I changed the timeline setting to display frames (in FCPX Preferences)
Identified a starting point where the presenter starts, added a marker
So, each file needed to be trimmed to that point.
I used the range tool to select everything before the presenter starts on a given track, and used Control + D to get the duration in frames.
Then I opened a copy of the source file with Quicktime 7
In the bottom left corner, changed the display to FRAMES
Then double click on the 0 frames, and type in the requried frame number to trim to
Then press Shift + Enter to go the that frame
Use the I key to make that the IN point
Option + Right Arrow to go to the end of the video
O key to set the OUT point
Edit - Trim to Selection
The original video is trimmed perfectly to that frame.
Did the same on each of the other videos & the client has files with the precise starting times.
I could have exported them out of FCPX, but that would take more processing time & the client was insisting on original files.
The biggest key was the Shift + Enter key to move the playhead to a specific frame in QT - 7
Move the playhead to a specific frame in Quicktime 7
Open a file in QT 7
On the far left edge of the timeline, click on drop down option and change the timecode display from Standard to Frames
Double Click on the frame number (ususally 0 if you've just opened the file)
Type in the reqired frame you want the playhead to move to
Use Shift + Enter(return) and the playhead will jump to that frame.