Trying to get non-flickering, non-blocking movie playback on PTB, the trick is to use non-blocking double buffering, keep showing the old frame until a new frame is available. Otherwise if you block, you miss flips waiting for the correct time, and if you don't block, then you get blank frames if you flip at FPS.

movietest.m

function movietest()

bgColour = 0.5;
screen = max(Screen('Screens'));
screenSize = [];

ptb = mySetup(screen,bgColour,screenSize);

filename='C:\Code\opticka\stimuli\monkey.mp4';
preloadsecs = [];
flags1 = [];
pixelformat = []; 
blocking = 0;
loop = 2;

tic
[movie, duration, fps, width, height] = Screen('OpenMovie', ptb.win, ...
	filename, [], preloadsecs, flags1, pixelformat);
fprintf('\n\n--->>> MOVIETEST: %s\n\t%f seconds duration, %f fps, w x h = %i x %i, in %ims\n', ...
	filename, duration, fps, width, height, round(toc*1e3));
fprintf('\t\t Blocking: %i | Loop: %i | Preloadsecs: %i | Pixelformat: %i | Flags: %i\n', blocking, loop, preloadsecs,...
	pixelformat,flags1);

Priority(MaxPriority(ptb.win)); %bump our priority to maximum allowed

otex = -1;
Screen('PlayMovie', movie, 1, loop)
vbl(1)=Screen('Flip', ptb.win);
tic
while vbl(end) < vbl(1) + 2
	texture = Screen('GetMovieImage', ptb.win, movie, blocking);
	if texture > 0
		if otex > 0; Screen('Close', otex); otex=-1;end
		Screen('DrawTexture', ptb.win, texture);
		otex = texture;
	elseif otex > 0
		Screen('DrawTexture', ptb.win, otex)
	end
	vbl(end+1) = Screen('Flip', ptb.win, vbl(end) + ptb.ifi/2);
end
if texture > 0; Screen('Close', texture); end
toc
figure;plot(diff(vbl)*1e3);title('VBL Times');ylabel('Time (ms)')
Screen('PlayMovie', movie, 0);
Screen('CloseMovie', movie);

Screen('Close', ptb.win);

%m = movieStimulus('fileName',filename,'blocking',blocking,'preloadSecs',preloadsecs,'loopStrategy',loop,'pixelFormat',pixelformat);
%m.run();

end

%----------------------
function ptb = mySetup(screen, bgColour, ws)

ptb.cleanup = onCleanup(@myCleanup);
PsychDefaultSetup(2); KbName('UnifyKeyNames');
Screen('Preference', 'SkipSyncTests', 0);
if isempty(screen); screen = max(Screen('Screens')); end
ptb.ScreenID = screen;
PsychImaging('PrepareConfiguration');
[ptb.win, ptb.winRect] = PsychImaging('OpenWindow', ptb.ScreenID, bgColour, ws, [], [], [], 1);

[ptb.w, ptb.h] = RectSize(ptb.winRect);
screenWidth = 405; % mm
viewDistance = 573; % mm
ptb.ppd = ptb.w/2/atand(screenWidth/2/viewDistance);
ptb.ifi = Screen('GetFlipInterval', ptb.win);
ptb.fps = 1 / ptb.ifi;
Screen('BlendFunction', ptb.win, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

end

%----------------------
function myCleanup()

disp('Clearing up...')
sca

end