New Segments

Microsoft DirectShow 9.0

New Segments

A segment is a group of media samples that share a common start time, stop time, and playback rate. The IPin::NewSegment method signals the start of a new segment. It provides a way for a source filter to inform downstream filters that the time and rate information has changed. For example, if the source filter seeks to a new point in the stream, it calls NewSegment with the new start time.

Some downstream filters use the segment information when they process samples. For example, in a format that uses interframe compression, if the stop time falls on a delta frame, the source filter may need to send additional samples after the stop time. This enables the decoder to decode the final delta frame. To determine the correct final frame, the decoder refers to the segment stop time. As another example, audio renderers use the segment rate along with the audio sampling rate to generate the correct audio output.

In the push model, the source filter initiates the NewSegment call. In the pull model, this is done by the parser filter. In either case, the filter calls NewSegment on the downstream input pin, which propagates the call to the next filter, until the call reaches the renderer. Filters must serialize NewSegment calls with other streaming calls, such as IMemInputPin::Receive.

Stream time resets to zero after each new segment. Time stamps on samples delivered after the segment start from zero.