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The Sample Grabber filter is a transform filter that can be used to grab media samples from a stream as they pass through the filter graph. If you simply want to grab a bitmap from a video file, it is easier to use the Media Detector MediaDet object. See Grabbing a Poster Frame for details. The Sample Grabber is more flexible, however, because it works with nearly any media type see ISampleGrabber::SetMediaType for the few exceptionsand offers more control to the application.
Create an instance of the Sample Grabber filter and addit to the filter graph. When you first create the Sample Grabber, it has no preferred media type. This means you can connect to almost any filter in the graph, but you would have no control over the type of data that it received.
Before building the rest of the graph, therefore, you must set a media type for the Sample Grabber, by calling the ISampleGrabber::SetMediaType method. When the Sample Grabber examples connects, it will compare this media type against the media type offered by the other filter. The only fields that it checks are the major type, subtype, and format type.
For example, the following code specifies uncompressed bit RGB video:. Now you can build the rest of the filter graph. Because the Sample Grabber will only connect using the media type you have specified, this lets you take advantage of the Filter Graph Manager's Intelligent Connect mechanisms when you build the graph.
For example, if you specified uncompressed video, you can connect a source filter to the Sample Grabber, and the Filter Graph Manager will automatically add the file parser and the decoder. Grabber examples following example uses the ConnectFilters helper function, which is listed in Connect Two Filters :.
The Sample Grabber is a transform filter, so the output pin must be connected to another filter. Often, you may simply want to discard the samples after you are done with them.
In that case, connect the Sample Grabber to the Null Renderer Filterwhich discards the data that it receives. Be aware that placing the Sample Grabber between a video decoder and the video renderer washington post coupon code significantly hurt rendering performance. The Sample Grabber is a trans-in-place filter, which means the output buffer is the same as the input buffer.
For video rendering, the output buffer is likely to be located on the graphics card, where read operations are much slower, compared with read operations in main memory. This article describes buffering mode.
Before using callback mode, be aware that the personal statement examples for resumes function must be quite limited.
Otherwise, it can drastically reduce performance or even cause deadlocks. This causes the Sample Grabber to halt after it receives the first media sample, which is useful if you want to grab a single frame from the stream. Note that the level of frame accuracy depends on the source. For example, seeking an MPEG file is often not frame accurate.
To run the graph as fast as possible, turn of the graph clock as described in Setting the Graph Clock. The following example enables one-shot grabber examples and buffering mode, runs the filter graph, and waits for completion. In buffering mode, the Sample Grabber stores a copy of every sample. Then allocate the array and call the method a second time to copy the buffer. The following example shows these steps. You will need to know the exact format of the data in the buffer.
The following example shows how to get the format information for an uncompressed video stream. This example uses the SafeRelease function to release interface pointers.
Using DirectShow Editing Services. Skip to main content. Exit focus mode. Theme Light. High contrast. Profile Bookmarks Collections Sign out. Run the Personnel statements The Sample Grabber operates in one of two modes: Buffering mode makes a copy of each sample before delivering the sample downstream.
Callback mode invokes an application-defined callback function on each sample. Note This example uses the SafeRelease function to release interface pointers. Is this page helpful? Yes No. Any additional feedback? Skip Submit.
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