How to split a binary file into different frames - matlab

Question

So I have a quite big binary file that contains the information of about 70 video frames.
I read the binary file into MATLAB using the following
fid = fopen('data.binary');
B = fread(fid,'int64');
fclose(fid);
But then the variable B still contains a huge number of data. So I was wondering how can we split the variable B such that I can get data from one frame only one by one. Like let's say 30 FPS.
Is that even possible?
Thanks
PS: the pixel precision is uint8 and the Frame size 424X512. This is the code I am using:
fid = fopen('C:\KinectData\Depth\Depth_Raw_0.binary');
B = fread(fid,'uint8');
fclose(fid);
B = uint8(B);
Z = B(1:217088)
n = 424; % No. of columns of T
BB = reshape(Z, n,[]);
BB = uint8(BB);
imshow(BB)
But the picture isn't quite there yet.

Answer 1

OK, so we know a few things given your comments:
Each frame is 424 x 512
The precision of each element in your video is uint8
This is a grayscale video, so colour is not going to be considered
I'm going to assume your data is read in row major format. Bear in mind that MATLAB reads in data in column major format if you want to read in the data as a matrix, so you'll have to do a transpose operation, and ensure that you read the data into a transposed matrix first.
What I'm going to do is put each frame into a cell entry inside a cell array. The reason why I'm doing this is because we don't know how many frames are really in your sequence. You said "70 or so" frames, and since we don't know the exact number, we will dynamically populate the cell array as we go.
The code you have written will predominantly be the same, but we're going to run a while loop until what we read in from file is empty. In the while loop, we will read one frame at a time and store it into the cell array. I'll also make a counter that counts the number of frames we have to for later, and you'll see why. As such:
%// Open the file
fid = fopen('C:\KinectData\Depth\Depth_Raw_0.binary');
col = 424; %// Change if the dimensions are not proper
row = 512;
frames = {}; %// Empty cell array - Put frames in here
numFrames = 0; %// Let's record the number of frames too
while (true) %// Until we reach the end of the file:
B = fread(fin, [col row],'uint8=>uint8'); %// Read in one frame at a time
if (isempty(B)) %// If there are no more frames, get out
break;
end
frames{end+1} = B.'; %// Transpose to make row major and place in cell array
numFrames = numFrames + 1; %// Count frame
end
%// Close the file
fclose(fid);
As such, if you want to access the ith frame, you would simply do:
frm = frames{i};
As an additional bonus, you can play this as a movie in MATLAB. What we can do is preallocate a movie structure that is compatible to play the movie, then when you run the movie command, this will play the frames for you. Let's specify a frame rate of 10 fps, so that it will play slow enough to see the results. Therefore, when you're done do something like this:
%// Preallocate the movie structure array
movieFrames(numFrames) = struct('cdata',[],'colormap',[]);
for idx = 1 : numFrames
img = frames{idx};
movieFrames(idx) = im2frame(cat(3, img, img, img));
end
figure;
imshow(movieFrames(1).cdata); %// Show first frame to establish figure size
movie(movieFrames, 1, 10); %// Play the movie once at 10 FPS
Note that movies can only be played in colour, and so you would have to make your grayscale image artificially into colour. A colour frame is a 3D matrix, where each 2D slice tells you the amount of red, green or blue. For grayscale, each of these slices are the same, and so you would just replicate each grayscale frame for each slice. I used cat to make the grayscale frame into a 3D matrix. I also use im2frame to convert each image into a movie frame structure compatible to be played with movie.
Small caveat
I don't have access to your binary file, so this code is untested. Use at your own risk!