First get the timescale of the movie you're working with (gettimescale message). Say your movie has a QT timescale of 600. That means that 600 QT time values == 1000 msecs. So 1200 QT time values would be 2 seconds, 1800 QT values would be 3 seconds, etc.
i have seen this patches using groove although i'm stuck in the interval=framerate relation i can't really see how it works
although i need to use sfplay because the files are too large to be loaded into ram, and since i'm stuck i haven't come with a reliable way to control quicktime frames or time through sfplay
sfplay~ has an optional position signal output.
enable that output and use that in place of the groove~ output.
sfplay's is millisec position, so you have to divide by 1000.0 and multiply by the timescale (usually 600), to get get the proper quicktime "time" (not "frame") attribute value based on millisecond time.