|Microsoft DirectShow 9.0|
The previewmode attribute specifies the preview mode for the group. If the value is TRUE, frames might be dropped during preview. Otherwise, no frames are dropped during preview. The default value is TRUE.
The following values are defined as TRUE:
1. The following values are defined as FALSE:
Under the default setting, frames are dropped while previewing slow effects or transitions, to keep the video synchronized with the audio. The video might look choppy as a result. Setting this attribute to FALSE forces every frame to render during preview, possibly resulting in the video becoming out of sync with the audio. Frames are never dropped when writing to a file.