AEIO_DrawSparseFrame (Writing plug-in)

Question

We are writing an import type plug-in for After effects.(AEGP)
In AEIO_DrawSparseFrame call we get an object to AEIO_DrawSparseFramePB.
typedef struct {
AEIO_Quality qual;
// CW adds 2 pad bytes here
AEIO_RationalScale rs;
A_Time tr;
A_Time duration;
A_Rect required_region; // empty rect means entire
AEIO_InterruptFuncs inter;
} AEIO_DrawSparseFramePB;
There is no mention of the above structure in the SDK help.
But what we could make out is that tr(A_Time) represents the frame time.
The problem which we are facing is that when we export the contents, we do not get consecutive frame times in calls to AEIO_DrawSparseFrame.
But we get frame times with a difference of 1 i.e we get 0, 2, 4, 6, 8 and so on, or sometimes the difference is 3 also.
But when we play the contents we get the consecutive frame times in tr parameter.
Pls guide on how to get/interpret the right frame times while playing/exporting/scrubbing.

Answer 1

there are two sample projects in the sdk that would be of interest to you.
1. IO (deals with importing and exporting of custom file types)
2. FBIO (the same as the above, but deals with frame sequences and not with movies)
there is one thing you should consider when doing this as an import plug-in:
as opposed to premier, that seeks the original file every time to display it, AE caches frames.
so even if you change the source, AE will not necessarily show that, until the "footage" is re loaded or AE starts recycling ram.
you can change the preferences of AE so that it doesn't cache anything, but then you seriously impair AE's performance.