{"id":1734,"date":"2013-07-30T23:01:53","date_gmt":"2013-07-31T02:01:53","guid":{"rendered":"http:\/\/tangopardo.com.ar\/2cf7\/?p=1734"},"modified":"2014-12-04T08:49:17","modified_gmt":"2014-12-04T11:49:17","slug":"using-the-gstreamer-controller-subsystem-from-python","status":"publish","type":"post","link":"https:\/\/tangopardo.com.ar\/2cf7\/2013\/07\/30\/using-the-gstreamer-controller-subsystem-from-python","title":{"rendered":"Using the Gstreamer Controller subsystem from Python."},"content":{"rendered":"

This is more or less a direct translation of the examples found at gstreamer\/tests\/examples\/controller\/*.c to their equivalents using the gi bindings for Gstreamer under Python. The documentation can be found here<\/a>. Reading the source also helps a lot.<\/p>\n

The basic premise is that you can attach a controller to almost any property of an object, set an interpolation function and give it pairs of (time, value) so they are smoothly changed. I’m using a pad as a target instead of an element just because it fits my immediate needs but it really can be any Element.<\/p>\n

First you need to import Gstreamer and initialize it:
\n
\n#!\/usr\/bin\/python
\nimport gi
\nimport sys
\nfrom gi.repository import GObject
\ngi.require_version('Gst', '1.0')
\nfrom gi.repository import Gst
\nfrom gi.repository import GstController
\nfrom gi.repository import Gtk
\nfrom gi.repository import GLib<\/p>\n

GObject.threads_init()
\nGst.init(sys.argv)<\/p>\n

<\/code><\/p>\n

Then create your elements. This is by no means the best way but lets me cut a bit on all the boilerplate.<\/p>\n


\np = Gst.parse_launch (\"\"\"videomixer name=mix ! videoconvert ! xvimagesink
\nvideotestsrc pattern=\"snow\" ! videoconvert ! mix.sink_0
\nvideotestsrc ! videoconvert ! mix.sink_1
\n\"\"\")<\/p>\n

m = p.get_by_name (\"mix\")
\ns0 = [pad for pad in m.pads if pad.name == 'sink_0'][0]
\ns0.set_property (\"xpos\", 100)
\n<\/code><\/p>\n

Here I created two test sources, one with bars and another with static that also has an horizontal offset. If we were to start the pipeline right now ( p.set_state (Gst.State.PLAYING) ) we would see something like this:<\/p>\n

\"captura_testinterpolation\"<\/a><\/p>\n

So far it works. Now I’d like to animate the alpha property of s0 (the sink pads of a videomixer have interesting properties like alpha, zorder, xpos and ypos). First we create a control source and set the interpolation mode:<\/p>\n

cs = GstController.InterpolationControlSource()
\ncs.set_property('mode', GstController.InterpolationMode.LINEAR)<\/code><\/p>\n

Then we create a control binding for the property we want to animate and add it to our element:<\/p>\n

cb = GstController.DirectControlBinding.new(s0, 'alpha', cs)
\ns0.add_control_binding(cb)<\/code><\/p>\n

It is worth noting that the same control source can be used with more than one control binding.<\/p>\n

Now we just need to add a couple of points and play:<\/p>\n

cs.set(0*Gst.SECOND, 1)
\ncs.set(4*Gst.SECOND, 0.5)
\np.set_state (Gst.State.PLAYING)<\/code><\/p>\n

If you are not running this from the interpreter remember to add GObject.MainLoop().run() , otherwise the script will end instead of keep playing. Here I’ve used absolute times, to animate in the middle of a playing state you need to get the current time and set the points accordingly, something like this will do most of the cases:<\/p>\n


\nstart = p.get_clock().get_time() # XXX: you better check for errors
\nend = start + endtime*Gst.SECOND
\n<\/code><\/p>\n

Avoiding too much bookkeeping<\/h4>\n

You can get the controller and control source of an element with:
\n
\ncontrol_binding = element.get_control_binding('property')
\nif control_binding:
\n    control_source = control_binding.get_property('control_source')
\n<\/code><\/p>\n","protected":false},"excerpt":{"rendered":"

This is more or less a direct translation of the examples found at gstreamer\/tests\/examples\/controller\/*.c to their equivalents using the gi bindings for Gstreamer under Python. The documentation can be found here. Reading the source also helps a lot. The basic premise is that you can attach a controller to almost any property of an object, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[51,13,24,4,22],"tags":[52,64],"class_list":["post-1734","post","type-post","status-publish","format-standard","hentry","category-opcode","category-electronica","category-hacks","category-python","category-software-libre","tag-gstreamer","tag-python"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/pmnbC-rY","_links":{"self":[{"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/posts\/1734","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/comments?post=1734"}],"version-history":[{"count":10,"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/posts\/1734\/revisions"}],"predecessor-version":[{"id":1745,"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/posts\/1734\/revisions\/1745"}],"wp:attachment":[{"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/media?parent=1734"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/categories?post=1734"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tangopardo.com.ar\/2cf7\/wp-json\/wp\/v2\/tags?post=1734"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}