Composite several frames into one

[cicero]

Greetings.

I'm looking for a reliable way to composite a bunch of video frames
into a single one on my server (arch linux amd64). As far as I know
``videomixer'' is sort of deprecated and everybody suggest ``compositor''.
Unfortunately compositor's performance is horrible in my case for some 
reason (on quite powerful
6th gen mobile Xeon, maybe I'm doing something wrong, but it fails to 
merge 10
frames into one 720p at 25 fps). On the other hand glvideomixer works as 
a charm,
however it fails to initialize egl context without Xorg server instance
running  (which is undesirable on a server). It fails with:

0:00:29.691145203 742 0x7f5b400e7190 WARN glbasefilter
gstglbasefilter.c:393:gst_gl_base_filter_decide_allocation: error:
Failed to initialize egl: EGL_NOT_INITIALIZED

0:00:38.723218316 549 0x7fe5bc0e69e0 INFO GST_ERROR_SYSTEM
gstelement.c:1938:gst_element_message_full_with_detils:<glcolorconvertelement2> 

posting message: Failed to initialize egl: EGL_NOT_INITIALIZED

0:00:38.723237521 549 0x7fe5bc0e69e0 WARN basetransform
gstbasetransform.c:974:gst_base_transform_do_buffer
pool:<glcolorconvertelement2> Subclass failed to decide allocation

even with EGL_PLATFORM=drm

Is there a way to make opengl elements work on a server without X server? Or
is there any way to improve compositor performance?

Here is my pipeline:

https://imgur.com/a/eAisO


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