Viewing QTMovie duration attributes?

Question

I've probably spent the last 2 weeks searching through Apple Quicktime documentation to resolve what seems like a pretty basic question, but to no avail. Here's the issue...

I've got several short QTMovie files each containing three tracks -- the usual two containing the sound and video, plus an extra video track holding subtitled text images (making two video tracks in all). If I select one of these tracks in Quicktime Pro and export it as an 'Movie To Image Sequence' I might find say, 142 stills spread throughout the duration of the movie. My search method also reports the correct total number of frames.

Now, I've learned that you can take single-frame images, add them to a QTMovie, and set their individual on-screen display times for however long you want using 'attributeForKey:QTMovieDurationAttribute'. But how on earth do I go about accessing that data again? (which essentially just seems like the reverse of this process).

In pseudo-code what I'm trying to do is something like:

{
select video track #2 ...
call up the first image in the sequence ...
access and note its on-screen duration setting ...
call up the second image ...
access and note its duration ...
... repeat until done.

}

I'm not after editing this data or anything -- just finding out how I can get access to individual frames in a video track ... and where the HECK this timing info is hiding inside the bowels of QT.

As a senior citizen I think I'm starting to get too old for this sort of thing and Quicktime is a big, often complex and confusing framework, so if anyone can help me out with some advice or (ideally) just a few lines of sample code here I'd really appreciate it. Thanks in advance :-)

Answer 1

Okay. After several more days of digging and experimentation I finally found the answer to my own question. To get the (next) subtitle image I used:

// access the subtitle track
Track theTrack = [self getVideoSubtitleTrack];

// set flags to find NEXT image (ignoring the current one)...
myFlags = nextTimeStep;
// ... and search forward from current position.
GetTrackNextInterestingTime(theTrack, myFlags, playheadPos, fixed1, &nextInterestingTime, NULL);

This only finds the start of an image object though, and iterating through the track finds the leading edge of each successive image. But I wanted the end time of the current text too.

After getting the start time, I experimented with the seven available flags and found that setting the flag to 'nextTimeTrackEdit' gets the end time.