How to check what videoscale plugin negotiates

Application Development
1

I have a video player pipeline scaling: playbin3 → videoscale → glinkbin → gtk4paintablesink.

The gtk4paintable sink is set as the paintable for a Gtk Picture after I set up the pipeline.

The picture’s set_size_request sets a width and height greater than the resolution of the video I play, but with the same aspect ratio.

The scaling seems to look OK on my screen (no jaggies or funny blurring) and the CPU usage stays low.

How can I see if videoscale is doing anything or if the paintablesink is just scaling?

2

Hi @patknight

To check the caps that the pipeline’s elements are negotiating, including the “videoscale”, you can add the “-v” option, for example:

gst-launch-1.0 -v playbin3 ! …

You will get something like this for the videoscale element, as well as for gtk4paintablesink:

/GstPipeline:pipeline0/GstVideoScale:videoscale0.GstPad:src: caps = video/x-raw, format=(string)A444_16LE, width=(int)320, height=(int)240, framerate=(fraction)30/1, multiview-mode=(string)mono, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string)progressive

/GstPipeline:pipeline0/GstVideoScale:videoscale0.GstPad:sink: caps = video/x-raw, format=(string)A444_16LE, width=(int)320, height=(int)240, framerate=(fraction)30/1, multiview-mode=(string)mono, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string)progressive

If you want to force a specific resolution in the gtk4paintablesink, you need to set the caps explicitly after the videoscale element, for example:

… ! videoscale ! video/x-raw,width=1920,height=1080 ! …

Regards.

3

Hi @luis.merayo

Thanks for the guidance. This is what I was looking for. In my app, I set up the pipeline programmatically, but I can go and play with using parse launch to see if I can make that work. I’ll also look into doing the equivalent using the APIs.

Cheers,
Pat

4

To close this off in case this is useful for someone else. The thing to do is create Caps and then use link_filtered to use them.

I ended up with (in Python, assume error checking and handling)

            video_bin = Gst.Bin()   # make a Bin that's going to act as the sink for playbin3
            video_bin.add(video_sink)   # the video_sink is in every pipeline and was created earlier
            if need_scale_plugin:
                scale_caps = Gst.caps_from_string(f"video/x-raw, width={width}, height={height}")
                scale_plugin = player_factory.make("videoscale", "videoscale")
                scale_plugin.set_property("method", ScalingMethod.CATROM)
                video_bin.add(scale_plugin)
                if not scale_plugin.link_filtered(video_sink, scale_caps):
                    raise RuntimeError("Unable to link scale to video sink")

Cheers
Pat

5

Side note to whom it could help checking caps negociation when pipeline is programatically built (this is what gst-launch-1.0 -v does), you can connect signal deep-notify to the pipeline before running it and attach a callback function (here just logging):

C/C++:

g_signal_connect(pipeline, “deep-notify”, G_CALLBACK(gst_object_default_deep_notify), NULL);

Python:

pipeline.connect(‘deep-notify’, verbose_deep_notify_cb, None)

6

Thanks for adding the helpful info and making the answer more complete.