[gst-devel] dynamic change element's parameter

[HaroldJRoth]

Stefan Kost wrote:
> 
> On 14.09.2010 16:37, Chandler Li wrote:
>> Thank you,
>> I paste the key point code to there,
>>
>> the old one caps:
>>                caps1 = gst_caps_new_simple ("video/x-raw-yuv",
>>   	      "format", GST_TYPE_FOURCC, GST_MAKE_FOURCC ('I', '4', '2', '0'),
>> 	      "width", G_TYPE_INT, 123,
>> 	      "height", G_TYPE_INT, 456,
>> 	      "framerate", GST_TYPE_FRACTION, 30, 1,
>> 	      NULL);
>> the new one caps:
>>               caps2 = gst_caps_new_simple ("video/x-raw-yuv",
>>   	      "format", GST_TYPE_FOURCC, GST_MAKE_FOURCC ('I', '4', '2', '0'),
>> 	      "width", G_TYPE_INT, 456,
>> 	      "height", G_TYPE_INT, 789,
>> 	      "framerate", GST_TYPE_FRACTION, 30, 1,
>> 	      NULL);
>> and the folowing code change caps:
>>                
>> gst_pad_set_blocked_async(pad,TRUE,my_blocked_callback,NULL);
>> 		gst_element_set_state(GST_ELEMENT(capsfilter2), GST_STATE_NULL);
>> 		g_object_set (G_OBJECT (capsfilter2), "caps",caps2,NULL);
>> 		gst_element_set_state(GST_ELEMENT(capsfilter2), GST_STATE_PLAYING);
>> 		gst_pad_set_blocked_async(pad,FALSE,my_blocked_callback,NULL);
>>   
> ohh, you can just set the caps. I mean just do:
> 
> g_object_set (G_OBJECT (capsfilter2), "caps",caps2,NULL);
> 
> Stefan
> 
> 

The above advice works great.

For absolute beginners, here's a code sample that details how to get the
capsfilter element reference:

        // We want to link the inputChain to the video queue using a
        // caps filter element.  That filter will allow us to adjust the
        // height and width used by the videoscaler at the end of the
        // the input chain (not shown here).
        //
        mVideoScaleFilter = gst_element_factory_make("capsfilter", NULL);
        g_assert(mVideoScaleFilter);

        // Predefined GstCaps makes no assumptions about width/height.
        //
        GstCaps* videoCaps = gst_caps_new_simple("video/x-raw-yuv",
"format",
			GST_TYPE_FOURCC, GST_MAKE_FOURCC('I', '4', '2', '0'), NULL);

        g_object_set(G_OBJECT(mVideoScaleFilter), "caps", videoCaps, NULL);

        // Now, add filter to pipeline, link it up
        //
        gst_bin_add_many(GST_BIN(mGstPipeline),
        		mVideoScaleFilter,
        		NULL);

        linkRes = gst_element_link_many( inputChain, mVideoScaleFilter,
mVideoQueue, NULL);
		if (!linkRes){
			// Inform logger of error!
        }

	// Discard caps reference.  GstElement references are object members,
	// they are unreferenced in the dtor.
	//
        gst_caps_unref(videoCaps);


AND here's how to set that filter later on.  'width' and 'height' are
function arguments.  Notice that this works with the pipeline in a PLAYING
state.

        GstCaps* videoCaps = gst_caps_new_simple("video/x-raw-yuv",
							"format", GST_TYPE_FOURCC, GST_MAKE_FOURCC('I', '4', '2', '0'),
							"width", G_TYPE_INT, width,
							"height", G_TYPE_INT, height,
							NULL);
        g_assert(videoCaps);
        g_assert(mVideoScaleFilter);
        g_object_set(G_OBJECT(mVideoScaleFilter), "caps", videoCaps, NULL);
        gst_caps_unref(videoCaps);


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