Thanks for the analysis, I don't know much about threads, processes, etc.. But I did further trials, that the issue occurs when the 2 monitors have different refresh rates. i.e. main monitor has 100Hz and the 2nd monitor has 50Hz. If I set both to 50Hz, the DWM hogging issue is gone. Also, if the video is not using DxVA acceleration (pure software decoding), no such issue neither. Do these give you more clue to the root cause?