extract key frames from video

I am writing a code having following steps to extract key frames:

1) Read frames from video (let us suppose we have 700 frames)

2) Now using 'ssim' function I am finding similarity between frame 1 and successive frames. For using 'ssim' a reference frame should be there. Initially I made the first frame as reference frame. Also I took the first frame as key frame. The next frame will be keyframe if similarity is less than some threshold 'T'.

3) Suppose My 80th frame has similarity less than 'T'. Now I want to make this frame as my reference frame. And also the for loop should start from this frame only means in this case now for loop will start from 80th frame and correspondingly will find similarity between successive frames i.e.from 81st onwards.

4) I have to repeat the process till last keyframe.

Attaching here the piece of code. Kindly suugest the ways to execute the above steps.

clc;
clear all;
close all;
tic;
%reading video frames
 vid=VideoReader('D:\project\Fingerspelling pics\vid6.mp4');
  numFrames = vid.NumberOfFrames;
   n=numFrames;
   % making a folder to save the frames
  Folder = 'D:\project\Fingerspelling pics\extframes\';
 % writing extracted frames into the specified folder
 for iFrame = 1:n
   frames = read(vid, iFrame);
   imwrite(frames, fullfile(Folder, sprintf('%06d.jpg', iFrame)));
 end 
FileList = dir(fullfile(Folder, '*.jpg'));

%here refernce is the 1st frame but I have to make such that reference should be current keyframe.
ref = imread('D:\project\Fingerspelling pics\extframes\000001.jpg');
 
k=0;
for iFile=1:length(FileList)
    aFile = fullfile(Folder, FileList(iFile).name)
    I3 = imread(aFile);
    x=ssim(I3,ref);
   y(k)=x;
   k=k+1;
end 

[Walter Roberson]

if x < T
  ref = I3;
  emit I3 as a key frame
 else
  emit differences between I3 and ref
 end

[NAVNEET NAYAN]

I am getting this error after I inserted your suugested lines into my code.

Undefined function or variable 'emit'.

Error in key_frame (line 35)

emit differences between I3 and ref

for iFile=1:length(FileList)
    aFile = fullfile(Folder, FileList(iFile).name)
%     aFile1 = fullfile(Folder, FileList())
    I3 = imread(aFile);
    I3=imcrop(I3,rec);
    k=k+1;
    x=ssim(I3,ref)
    if x < 0.86
        ref = I3;
        emit I3 as a key frame
    else
         emit differences between I3 and ref
    end
   y(k)=x
%    if y
%     a(k)=aFile(iFile)
end

[Walter Roberson]

emit is obviously pseudo code here. Replace with appropriate code to accomplish what the line says.

[NAVNEET NAYAN]

yeah..yeah got it...thanks