Querying for Seeking Capabilities

Querying for Seeking Capabilities

Microsoft® DirectShow® supports seeking through the IMediaSeeking interface. The Filter Graph Manager exposes this interface, but the seeking functionality is always implemented by filters in the graph.

Some data cannot be seeked. For example, you cannot seek a live video stream from a camera. If a stream is seekable, however, there are various types of seeking it might support. These include:

• Seeking to an arbitrary position in the stream.
• Retrieving the duration of the stream.
• Retrieving the current position within the stream.
• Playing in reverse.

The IMediaSeeking interface defines a set of flags, AM_SEEKING_SEEKING_CAPABILITIES, that describe the possible seeking capabilities. To retrieve the stream's capabilities, call the IMediaSeeking::GetCapabilities method. The method returns a bitwise combination of flags. The application can test them using the & (bitwise AND) operator. For example, the following code checks whether the graph can seek to an arbitrary position:

DWORD dwCap = 0;
HRESULT hr = pSeek->GetCapabilities(&dwCap);
if (AM_SEEKING_CanSeekAbsolute & dwCap)
{
    // Graph can seek to absolute positions.
}