Copy the video list (m3u) file to the /usr/share/sddm/themes/breeze-slider2/VideoList/VideoListBackground/

and

add the list name to the 'videoFile' key
Example: videoFile=VideoListBackground/Test-Video-Playlist.m3u

[General]
---Standard Breeze---
type=color
color=black
background=
---Sliding cover---
coverColor=#80000000
coverWaitTime=180000
coverClock=components/ConfigurableClock.qml
clockX=100
clockY=50
coverClockTimeFormat=HH:mm:ss
coverClockTimePointSize=32
coverClockDateFormat=dd-MM-yyyy
coverClockDatePointSize=18
coverSuspenButton=system-suspend
coverRebootButton=system-reboot
coverShutdownButton=system-shutdown
coverSearchButton=system-search
---Extra background---
extraBackground=VideoList/VideoPlayList.qml
---VideoList background
videoFile=
videoBackgroundColor=black
videoVolume=0.9
videoShuffle=0
videoFillMode=PreserveAspectCrop
infoCorner=corner3
infoTextBoxColor=#4d000000
infoFontSize=12
infoTextColor=white
---Background Clocks----
backgroundClock=BackgroundClocks/FixedClock.qml
backgroundClockBackgroundColor=#80000000
backgroundClockBackgroundRadius=0
backgroundClockX=0
backgroundClockY=0
backgroundClockTimeFormat=HH:mm:ss
backgroundClockTimePointSize=32
backgroundClockTimeTextColor=white
backgroundClockDateFormat=dd-MM-yyyy
backgroundClockDatePointSize=18
backgroundClockDateTextColor=lightgray
