Debugging vlc/openwrt/aarch64-Mali T820 (Panfrost)

[rossbcan]

Hi;

I am in process of debugging vlc for openwrt / x11

VLC media player - 3.0.18 Vetinari
uname -a: Linux SecureOffice 5.15.41-flippy-73+o #123 SMP PREEMPT Wed May 18 17:08:50 CST 2022 aarch64 GNU/Linux (ophub)

What works: can stream BigBuckBunny.mp4 and individual IP cameras from network
What not sure of: hardware acceleration
What does not work: montage of IP cameras. Suspect scaling / transcode / something broken in video pipeline. Looking for hints why / how to debug.
Processor: Amlogic S912

CAUTION: vlc newbie, built with contrib / openwrt packages hybrid approach (openwrt packages - if exist used instead of contrib ones).
SUSPICIAN: IFFY config for some OpenWrt packages breaking vlc

vlc command line: vlc -I dummy --vlm-conf /root/ipcam_4x4_mosaic.vlm --rtsp-frame-buffer-size 512000

ipcam_4x4_mosaic.vlm:

new channel1 broadcast enabled
setup channel1 option rtsp-tcp=enabled
setup channel1 input "rtsp://admin:passwd@192.168.2.31:554/0"
setup channel1 output #duplicate{dst=mosaic-bridge{id=1},select=video}

new channel2 broadcast enabled
setup channel2 option rtsp-tcp=enabled
setup channel2 input "rtsp://admin:passwd@192.168.2.32:554/0"
setup channel2 output #duplicate{dst=mosaic-bridge{id=2},select=video}

new channel3 broadcast enabled
setup channel3 option rtsp-tcp=enabled
setup channel3 input "rtsp://admin:passwd@192.168.2.33:554/11"
setup channel3 output #duplicate{dst=mosaic-bridge{id=3},select=video}

new channel4 broadcast enabled
setup channel4 option rtsp-tcp=enabled
setup channel4 input "rtsp://admin:passwd@192.168.2.34:554/11"
setup channel4 output #duplicate{dst=mosaic-bridge{id=4},select=video}

new mosaic broadcast enabled
setup mosaic input file:///root/background_1920x1080.png

setup mosaic option image-duration=-1
setup mosaic option image-fps=10
setup mosaic output #transcode{sfilter=mosaic{width=1920,height=1080,rows=2,cols=2,borderw=2,borderh=2,position=1,order="1,2,3,4"},vcodec=mp4v}:display

control channel1 play
control channel2 play
control channel3 play
control channel4 play
control mosaic play

What I observe:
-vlc is happily consuming packets from cameras (tcpdump)
-the background is displayed at proper size
-usually nothing, not even empty screen areas displayed for cameras. Sometimes see colored rectangles, not in proper position or size.
-occasionally, OOM killer (consumes all memory) activates and shuts down vlc
-no missing library symbols, no segfaults. Is missing libvdpau_meson.so (internet research indicates this is a created lib name, many missing libvdpau_X.so posts, does not affect functionality - please confirm)

Here's vlc.log. Newbie, so don't (yet) understand info flow and what it means:
https://www.rossco.org/Downloads/Files/vlc.log

Could really use some hints.

Thanks;
Bill