Help needed writing basic GstBaseSrc plugin for non generic video capture card

[pierre gousseau]

Hi All,I have a non generic audio video capture device with multiple inputs and i am trying to integrate it as my first gstreamer plugin.To start simple i am only aiming at creating an element with one video source. So I am extending GstBaseSrc.The device provide mmap yuv buffers in either PAL or NTSC resolution through ioctl calls.I have tried to take as an example the v4l2src source code.i test it with the commandgst-launch-0.10 myfilter device="/dev/xecap0" video-mode=0 chan-bitmap=0xffff chan-select=0 ! fakesinkAnd get the following/********************BEGIN**********************/Setting pipeline to PAUSED ...Pipeline is live and does not need PREROLL ...Setting pipeline to PLAYING ...New clock: GstSystemClock(gst-launch-0.10:854): GStreamer-CRITICAL **: gst_pad_push: assertion `GST_IS_BUFFER (buffer)' failedERROR: from element /pipeline0/myfilter0: Internal data flow error.Additional debug info:gstbasesrc.c(2165): gst_base_src_loop (): /pipeline0/myfilter0:streaming task paused, reason error (-5)Execution ended after 426026 ns.Setting pipeline to PAUSED ...Setting pipeline to READY ...(gst-launch-0.10:854): GStreamer-CRITICAL **: gst_mini_object_unref: assertion `mini_object->refcount > 0' failedgst_myfilter_stoppedSetting pipeline to NULL ...FREEING pipeline .../********************END***********************/With gst-debug=*:3, everything seems fine until i get the following warning and the pipeline stops .../********************BEGIN**********************/(gst-launch-0.10:796): GStreamer-CRITICAL **: gst_pad_push: assertion `GST_IS_BUFFER (buffer)' failed0:00:00.211305419   796 0x929a770 INFO               basesrc gstbasesrc.c:2114:gst_base_src_loop:<myfilter0> pausing after gst_pad_push() = error0:00:00.211320520   796 0x929a770 WARN               basesrc gstbasesrc.c:2165:gst_base_src_loop:<myfilter0> error: Internal data flow error.0:00:00.211328857   796 0x929a770 WARN               basesrc gstbasesrc.c:2165:gst_base_src_loop:<myfilter0> error: streaming task paused, reason error (-5)/********************END***********************/I have implemented the following methodsgstbasesrc_class->set_caps = GST_DEBUG_FUNCPTR (gst_myfilter_set_caps);gstbasesrc_class->start = GST_DEBUG_FUNCPTR (gst_myfilter_start);gstbasesrc_class->stop = GST_DEBUG_FUNCPTR (gst_myfilter_stop);gstbasesrc_class->create = GST_DEBUG_FUNCPTR (gst_myfilter_create);I initialise the buffer in the set_caps method like this:static gbooleangst_myfilter_set_caps (GstBaseSrc * src, GstCaps * caps){     .     .     .     if (!gst_pad_set_caps (src->srcpad, caps))    {        GST_WARNING ("gst_myfilter_set_caps caps negotiation failed %" GST_PTR_FORMAT "from elem",                caps, GST_ELEMENT_NAME(src));        return FALSE;    }    .    .    .    GST_BUFFER_DATA (filter->my_buffer) = (guchar*)dev_buf;    GST_BUFFER_SIZE (filter->my_buffer) = (filter->video_mode == 0)?704*576*2:704*480*2;    GST_BUFFER_FLAG_SET (filter->my_buffer, GST_BUFFER_FLAG_READONLY);    gst_buffer_set_caps (GST_BUFFER (filter->my_buffer), caps);   return TRUE;}Here is the create method, it always seems to get called 3 times ok untils the error shows which puzzle me the most.static GstFlowReturngst_myfilter_create (GstBaseSrc * basesrc, guint64 offset, guint length,    GstBuffer ** buffer){    Gstmyfilter *src;    GstState state = GST_STATE (basesrc);    if(state != GST_STATE_PLAYING)    {        return GST_FLOW_WRONG_STATE;    }    src = GST_MYFILTER (basesrc);    gchar * dev_buf = NULL;    dev_error dev_ret = dev_get_framebuffer(src->chan_select, src->dev_handle, &dev_buf);    if(dev_ret == DEV_ERROR || dev_buf == NULL)    {        return GST_FLOW_ERROR;    }    GST_BUFFER_OFFSET (src->my_buffer) = src->offset++;    GST_BUFFER_OFFSET_END (src->my_buffer) = src->offset;    GST_BUFFER_TIMESTAMP (src->my_buffer) = GST_CLOCK_TIME_NONE;    GST_BUFFER_DATA (src->my_buffer) = (guint8*)dev_buf;    *buffer = src->my_buffer;    return GST_FLOW_OK;}Any ideas why the (gst-launch-0.10:796): GStreamer-CRITICAL **: gst_pad_push: assertion `GST_IS_BUFFER (buffer)' failed error shows up ?Regards,Pierre 		 	   		  
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