CBaseRenderer Class

The CBaseRenderer class is a base class for implementing renderer filters. It supports one input pin, implemented by the CRendererInputPin class. To use this class, declare a derived class that inherits CBaseRenderer. At a minimum, the derived class must implement the following methods, which are declared as pure virtual in the base class:

• CBaseRenderer::CheckMediaType: Accepts or rejects proposed media types. The filter calls this method during the pin connection process.
• CBaseRenderer::DoRenderSample: Renders a sample. The filter calls this method for every sample that it receives while running.

The base class handles state changes and synchronization issues. It also schedules samples for rendering, although it does not implement any quality-control measures. The base class also declares several "handler" methods. These are methods that the filter calls at specific points in the streaming process. They do nothing in the base class, but the derived class can override them. In the table that follows, they are listed under the heading Public Methods: Handlers.

The CBaseRenderer::OnReceiveFirstSample handler deserves special mention. The filter calls this method if it receives a sample while the filter is paused. That can occur if the graph switches from stopped to paused, or if the graph is seeked while paused. Video renderers typically use the sample to display a still frame. When the filter switches from paused to running, it sends the same sample to the CBaseRenderer::DoRenderSample method, as the first sample in the stream.

The CBaseRenderer class exposes the IMediaSeeking and IMediaPosition interfaces through the CRendererPosPassThru object. It passes all seek requests to the next filter upstream.

Scheduling

When the upstream filter calls the input pin's IMemInputPin::Receive method to deliver a sample, the pin passes this call to the filter's CBaseRenderer::Receive method. The filter either drops the sample, renders it immediately, or schedules it for rendering.

If the sample has no time stamps, or if no reference clock is available, the filter renders the sample immediately. Otherwise, the filter calls the CBaseRenderer::ShouldDrawSampleNow method to determine what to do. By default, the sample is scheduled based on its time stamps. The derived class can override ShouldDrawSampleNow to support quality control.

To schedule a sample, the filter calls the IReferenceClock::AdviseTime method, which creates an advise request. The Receive method then blocks until the scheduled time, or until the filter changes state. Blocking prevents the upstream filter from delivering more samples until the current sample is rendered.

When the upstream filter calls the IPin::EndOfStream method to signal the end of the stream, the filter sends an EC_COMPLETE event to the filter graph manager. The filter waits for the current sample's stop time before sending the event.

Requirements

Header: Declared in Renbase.h; include Streams.h.

Library: Use Strmbase.lib (retail builds) or Strmbasd.lib (debug builds).