@Number_5
Can you try with quotes (single, double) ?
omxplayer --avdict rtsp_transport:tcp --win 786,424,1138,666 --live --video_queue 4 --fps 30 --no-osd "rtsp://admin:roland!?1971@192.168.2.108:80/cam/realmonitor?channel=2&subtype=0"
omxplayer --avdict rtsp_transport:tcp --win 786,424,1138,666 --live --video_queue 4 --fps 30 --no-osd 'rtsp://admin:roland!?1971@192.168.2.108:80/cam/realmonitor?channel=2&subtype=0'
when the command works, but still no video, then add --genlog
omxplayer --genlog --avdict rtsp_transport:tcp --win 786,424,1138,666 --live --video_queue 4 --fps 30 --no-osd 'rtsp://admin:roland!?1971@192.168.2.108:80/cam/realmonitor?channel=2&subtype=0'
This will creat a log file called omxplayer.log under the directory where you started omxplayer.