Build AGL for AGL Reference Platform board (h3ulcb machine with agl-refhw-h3 feature). Enable multimedia and H.264 as described in https://docs.automotivelinux.org/en/master/#0_Getting_Started/2_Building_AGL_Image/5_3_RCar_Gen_3/#11-supplementary-information:

MACHINE_FEATURES_append = " multimedia"
DISTRO_FEATURES_append = " h264dec_lib"

Use 640 x 360, 1MB Big Buck Bunny from https://test-videos.co.uk/bigbuckbunny/mp4-h264:
https://test-videos.co.uk/vids/bigbuckbunny/mp4/h264/360/Big_Buck_Bunny_360_10s_1MB.mp4

1. Put it to /media/test and reboot.
2. Open mediaplayer and press play button.

Problem: button changes from triangle (play) to two vertical lines (pause) but no video on screen. Nothing in logs too.