Gstreamer dev : custom source based on basesrc

Tue Jan 22 14:01:23 UTC 2019

Hi,

Thanks for your good answer.

If I well understand, i just keep the "fill" function like that:

/* ask the subclass to fill the buffer with data from offset and size */
static GstFlowReturn
gst_pciesrc_fill (GstBaseSrc * src, guint64 offset, guint size, 
GstBuffer * buf)
{
   GstPciesrc *pciesrc = GST_PCIESRC (src);

   GST_DEBUG_OBJECT (pciesrc, "fill");

   if(fd != -1)
   {
       GstMapInfo info;

     //Read the global device
     gst_buffer_map (buf, &info, GST_MAP_WRITE);

     int rc = read(fd, info.data, info.size);

     gst_buffer_unmap (buf, &info);

     GST_DEBUG_OBJECT (pciesrc, "info.size = %d", info.size);
     GST_DEBUG_OBJECT (pciesrc, "rc = %d", rc);
   }

   return GST_FLOW_OK;
}

But i get many errors :

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_caps_can_intersect: 
assertion 'GST_IS_CAPS (caps2)' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_unref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_pad_template_new: 
assertion 'caps != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_unref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: 
gst_element_request_compatible_pad: assertion 'GST_IS_PAD_TEMPLATE 
(templ)' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_object_unref: 
assertion 'object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_caps_can_intersect: 
assertion 'GST_IS_CAPS (caps1)' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_unref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3616): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed
WARNING: erroneous pipeline: could not link pciesrc0 to d
root at cl-som-imx8:~# export GST_DEBUG=pciesrc*:5
root at cl-som-imx8:~# gst-launch-1.0 pciesrc ! decodebin name=d d. ! queue 
! kmssink d. ! queue ! audioconvert ! alsasink
0:00:00.101927543  3618       0x674ca0 DEBUG pciesrc 
gstpciesrc.c:409:gst_pciesrc_query:<pciesrc0> query

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_caps_can_intersect: 
assertion 'GST_IS_CAPS (caps2)' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_unref: 
assertion 'mini_object != NULL' failed
0:00:00.103476261  3618       0x674ca0 DEBUG pciesrc 
gstpciesrc.c:409:gst_pciesrc_query:<pciesrc0> query

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_pad_template_new: 
assertion 'caps != NULL' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_unref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: 
gst_element_request_compatible_pad: assertion 'GST_IS_PAD_TEMPLATE 
(templ)' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_object_unref: 
assertion 'object != NULL' failed
0:00:00.103686021  3618       0x674ca0 DEBUG pciesrc 
gstpciesrc.c:409:gst_pciesrc_query:<pciesrc0> query

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_caps_can_intersect: 
assertion 'GST_IS_CAPS (caps1)' failed

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_unref: 
assertion 'mini_object != NULL' failed
0:00:00.103875861  3618       0x674ca0 DEBUG pciesrc 
gstpciesrc.c:409:gst_pciesrc_query:<pciesrc0> query

(gst-launch-1.0:3618): GStreamer-CRITICAL **: gst_mini_object_ref: 
assertion 'mini_object != NULL' failed
WARNING: erroneous pipeline: could not link pciesrc0 to d
root at cl-som-imx8:~#

BR

Frédéric

Le 22/01/2019 à 11:01, Edgar Thier a écrit :
> Hi,
>
> Gstreamer Buffer management consists out of multiple parts:
>
> - The GstBufferPool - It contains all buffers that will be used by your src. Unless you have a good
>    reason to implement it, use the default implementation, like you already are.
> - The single GstBuffer - consisting out of MetaData, timestamps and a pointer to GstMemory,
>    aka you actual image.
> - Your image buffer - This can be allocated be gstreamer or externally, depending on your setup.
>    Most sources i have seen (usb/firewire/network) allocate buffers in their backend and give
>    a pointer to the buffer to gstreamer.
>
> As is documented
> (https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer-libs/html/GstPushSrc.html)
> default sources will call create, which implicitly calls alloc and then fill.
> That means you do not have to overwrite all functions.
> By overwriting create the default implementations for alloc/fill will not be called.
> You will have to call them manually or implement their functionality in create itself.
>
> Depending on your setup you can call `gst_buffer_new_wrapped_full` for your existing buffer.
> This will use the GstBuffer from the GstBufferPool that you receive in create and use
> the image pointer you provide for the pipeline.
>
> Examples for this would be:
>
> https://github.com/AravisProject/aravis/blob/master/gst/gstaravis.c#L351
>
> https://github.com/TheImagingSource/tiscamera/blob/master/src/gstreamer-1.0/gsttcamsrc.cpp#L1351
>
> Both execute extra steps that can be ignored. And both allocate their image buffer externally in
> their backends.
>
> The other way would be to have gstreamer allocate a buffer for you by calling alloc,
> filling that buffer with an image and delivering that. I have not worked with this method as of yet,
> so I cannot offer you details or examples.
>
> If I got any details wrong, please feel free to correct me.
>
> -Edgar
>
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