How to extract frames from a .mp4 video?

Hi I am trying to combine two videos in matlab. The first video is a clock moving with a green background. The second video is a black video moving in what it looks like is space. I am trying to extract the frames and make the second video the background to the first video. Using the code below only extracts the first frame, how can i extract all frames?

outputFolder1=('video');

v1=VideoReader('Clock.mp4');

vid1Frames=readFrame(v1);

for frame=1:size(vid1Frames,4)

outputBaseFileName=sprintf('%3.3d.png',frame);

outputFullFileName=fullfile(outputFolder1,outputBaseFileName);

imwrite(vid1Frames(:,:,:,frame),outputFullFileName,'png');

end

Answer 1

[Stephan]

outputFolder1=('video');
v1=VideoReader('Clock.mp4');
vid1Frames=read(v1);
for frame=1:size(vid1Frames,4)
outputBaseFileName=sprintf('%3.3d.png',frame);
outputFullFileName=fullfile(outputFolder1,outputBaseFileName);
imwrite(vid1Frames(:,:,:,frame),outputFullFileName,'png');
end

Answer 2

[Boyuan Li]

Somehow the function readFrame() only read the first available frame instead of the whole video.

outputFolder1=('video');

v1=VideoReader('Clock.mp4');

while hasFrame(v1)

frame=readFrame(v1);

outputBaseFileName=sprintf('%3.3d.png',frame);

outputFullFileName=fullfile(outputFolder1,outputBaseFileName);

imwrite(frame,outputFullFileName,'png');

end