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ICaptureGraphBuilder2::RenderStream

  • Articolo
 
Microsoft DirectShow 9.0

ICaptureGraphBuilder2::RenderStream

The RenderStream method connects an output pin on a source filter to a sink filter, optionally through an intermediate filter.

Syntax

  HRESULT RenderStream(
  const GUID *pCategory,
  const GUID *pType,
  IUnknown *pSource,
  IBaseFilter *pIntermediate,
  IBaseFilter *pSink
);

Parameters

pCategory

[in] Pointer to a member of the AMPROPERTY_PIN_CATEGORY structure of the Pin Property Set property set, specifying a pin category; or NULL to use any pin, regardless of category. Typical values include the following.

  • PIN_CATEGORY_CAPTURE
  • PIN_CATEGORY_PREVIEW
  • PIN_CATEGORY_CC

pType

[in] Pointer to a major-type GUID that specifies the media type of the output pin; or NULL to use any pin, regardless of media type. For a list of possible values, see Major Types.

pSource

[in] Specifies a pointer to the starting filter for the connection, or to an output pin.

pIntermediate

[in] Pointer to the IBaseFilter interface of an intermediate filter, such as a compression filter. Can be NULL.

pSink

[in] Pointer to the IBaseFilter interface of a sink filter, such as a renderer or mux filter. If the value is NULL, the method uses a default renderer (see Remarks).

Return Values

Returns an HRESULT value. Possible return values include the following.

Return code Description
S_OK Success.
VFW_S_NOPREVIEWPIN Preview was rendered through the Smart Tee Filter.
E_FAIL Failure.
E_INVALIDARG Invalid argument.
E_POINTER NULL pointer argument.
VFW_E_NOT_IN_GRAPH A filter is not in the filter graph. This error can occur if you did not call AddFilter to add pSource, pIntermediate, or pSink to the graph. It can also occur if you did not call SetFiltergraph to connect your graph to the Capture Graph Builder; in this case, the Capture Graph Builder object automatically creates its own filter graph. See About the Capture Graph Builder.

Remarks

This method renders a stream by connecting two or more filters together in a chain:

  • The pSource parameter specifies the start of the chain, either a filter or an output pin.
  • The pIntermediate parameter specifies an intermediate filter, typically a compression filter. This parameter can be NULL.
  • The pSink parameter specifies the filter at the end of the chain. Typically, this filter is either a renderer for preview, or a mux for file capture.

The method connects pSource to pIntermediate, and then connects pIntermediate to pSink. If pIntermediate is NULL, the method just connects pSource to pSink. All of the filters specified by pSource, pIntermediate, and pSink must be added to the graph prior to calling the method. The method uses Intelligent Connect, so additional filters such as decoders might be added to the graph.

If the pSink parameter is NULL, the method tries to use a default renderer. For video it uses the Video Renderer, and for audio it uses the DirectSound Renderer.

If pSource is a filter, the method searches for an output pin on that filter. In that case, use the pCategory and pType parameters to narrow the search. For example, if a filter has separate pins for preview and capture, you can specify either PIN_CATEGORY_CAPTURE or PIN_CATEGORY_PREVIEW. If pSource is an output pin, set the pCategory and pType to NULL.

In all cases, the method searches for unconnected pins. If more than one pin meets the specified criteria, the method uses the first such pin that it finds.

Note that for DV capture, if the media type is MEDIATYPE_Interleaved and the pSink parameter is NULL, the method splits the interleaved stream into an audio stream and a video stream, and renders both of those streams.

The RenderStream method handles many of the details required for capture graphs:

Smart Tee. Some capture filters have a capture pin but no preview pin. To preview, the capture pin must be connected to the Smart Tee Filter. This filter splits the data into two streams, a capture stream and a preview stream. When you specify PIN_CATEGORY_PREVIEW or PIN_CATEGORY_CAPTURE, the method inserts a Smart Tee filter if one is needed. Then it renders the specified stream on the Smart Tee filter. If you render a preview stream and the method uses a Smart Tee filter, it returns VFW_S_NOPREVIEWPIN.

Closed Captioning. You can use this method to capture or preview closed captioning. Some capture filters deliver Vertical Blanking Interval (VBI) data, others deliver closed captioning data. To handle either case, call the method twice, once using PIN_CATEGORY_VBI and once using PIN_CATEGORY_CC. The method inserts any filters needed to convert VBI data to closed captioning. To preview the data, set the pSink parameter to NULL. To capture the data to a file, use the multiplexer filter's IBaseFilter interface pointer. You can capture and preview the data in the same graph. Call the method once using NULL and again using the multiplexer. Set the pIntermediate parameter to NULL.

Video Port Pins. Filters that work with video port extension (VPE) video capture hardware might have video port pins (PIN_CATEGORY_VIDEOPORT) instead of preview pins. For preview or capture to work, a video port pin must connect to the Overlay Mixer Filter. The method handles this detail. You do not have to specify PIN_CATEGORY_VIDEOPORT. Specify PIN_CATEGORY_PREVIEW or PIN_CATEGORY_CAPTURE, and the method will connect the pin correctly. In a similar way, some filters deliver VBI data using video port pins (PIN_CATEGORY_VIDEOPORT_VBI). As with PIN_CATEGORY_VIDEOPORT, the method handles this detail. You do not have to specify PIN_CATEGORY_VIDEOPORT_VBI.

Supporting Filters. If a capture device uses a Windows Driver Model (WDM) driver, the graph may require certain filters upstream from the WDM Video Capture Filter, such as a TV Tuner Filter or an Analog Video Crossbar Filter. If this method successfully renders the stream, it also inserts any WDM filters that are required in your graph. The method queries the input pins on the capture filter to determine what mediums they support, and connects them to matching filters.

Example Code

For a typical capture graph, connect the preview pin to the default renderer, with no intermediate filter:

// Video: 
pBuilder->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, 
    pCaptureFilter, NULL, NULL); 
// Audio:
pBuilder->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Audio, 
    pCaptureFilter, NULL, NULL);

Connect the capture pin to a mux filter or file writer filter, depending on what type of file you wish to output. For AVI files, use the AVI Mux filter. For ASF files, use the WM ASF Writer filter. Typically, you will get a pointer to this filter from the ppf parameter of the ICaptureGraphBuilder2::SetOutputFileName method.

pBuilder->SetOutputFileName(&MEDIASUBTYPE_Avi, L"C:\\Example.avi", 
    &ppf, &pSink);
pBuilder->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video,
    pCaptureFilter, NULL, ppf);

File Sources. You can use this method to transcode or recompress a file. The following discussion assumes that the file has at most one video stream and one audio stream, or else a single interleaved stream. Otherwise, the method will not work correctly.

A file source has one output pin, so set pCategory and pType to NULL. Call the method twice—once to render the video stream, and once to render the audio stream. The first call connects the source filter to a parser filter and renders one of the parser filter's output pins. The second call renders the parser's remaining output pin. If you are compressing one stream but not the other, make sure to specify the compressor filter in the first call. The method will automatically pick the correct stream based on the compression type.

pBuilder->RenderStream(NULL, NULL, pSrc, pCompressor, pMux);
pBuilder->RenderStream(NULL, NULL, pSrc, NULL, pMux);

For a complete example, see Recompressing an AVI File.

Requirements

Header: Declared in Strmif.h; include Dshow.h.

Library: Use Strmiids.lib.

See Also