ref_iface_IVDXVideoPrefetcher_PrefetchFrameSymbolic

VirtualDub Plugin SDK 1.2

IVDXVideoPrefetcher interface

IVDXVideoPrefetcher:: PrefetchFrameSymbolic

Identifies the symbolic source frame associated with an output frame.

void PrefetchFrameSymbolic(sint32 srcIndex, sint64 frame);

Parameters

srcIndex	Index of source stream containing symbolic frame. Must be zero.
frame	Frame number of symbolic frame.

Thread safety

This method is not thread-safe.

Errors

Errors may not be returned from this function (see SetError()).

Remarks

The symbolic frame is the source frame most associated with the output frame. For instance, for a noise reduction filter that looks at previous and next frames (three frame window), the symbolic frame is the center frame. This allows for reasonable behavior whenever the filter must be bypassed, such as when side-by-side source/output windows are displayed.

If the symbolic frame is not explicitly provided, the host assumes that it is the average of the frame numbers of all prefetched frames. This is the same as the prefetched frame when only one source frame is requested and provides reasonable behavior for all filters that request a centered source window of frames. For filters that don't fit these criteria, such as those which sometimes omit unnecessary frames or otherwise have lopsided source windows, explicit symbolic fetching is needed.

VirtualDub specific: The symbolic frame is used as the direct prefetch frame whenever filters are forcibly bypassed by setting the video mode to Direct Stream Copy.

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Copyright (C) 2007-2012 Avery Lee.