First, documentation in the source code is not correct here:

https://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/ext/gl/gstglimagesink.c#n538

The arguments are context and sample.


Secondly, it seems that GstVideoAffineTransformationMeta is always NULL. In an Android 6.0.1 Gstreamer-master-git tutorial-5-derived application, I have:


g_signal_connect(G_OBJECT(data->glimagesink), "client-draw", G_CALLBACK(client_draw_cb), data);


static gboolean client_draw_cb(GstElement *sink, GLuint texture, GstSample *sample, CustomData *data) {

GstBuffer *buf = gst_sample_get_buffer(sample);
GstVideoAffineTransformationMeta *atm = gst_buffer_get_video_affine_transformation_meta(buf);
//atm is NULL all the time
atm = gst_buffer_add_video_affine_transformation_meta(buf);
//atm is NULL again

GstVideoAffineTransformationMeta is null and it can't be created.


To give the big picture, my objective is to crop the video. I tried glOrthof but as I return FALSE because I don't want to deal with the texture, it's discarded by the original code. Fair enough. So I wanted to use a GstVideoAffineTransformationMeta. I can't access or create any GstVideoAffineTransformationMeta in this callback.