How to add caption/subtitles to Video in MATLAB

                                    In my previous post, I discussed about how to create videofrom still images and now we can add subtitles to the video. I used the ‘text’ function to add the subtitles.

The procedure to add subtitles to the Video:

·         Read an video file

·         Read each video frame data

·         Add text to each frame using the syntax ‘text(x,y,string)’.

·         Use imshow to display the image.

·         Get the frame from the figure displayed.

MATLAB CODE:

%Input a Video file

obj=mmreader('Poem.avi');

A=read(obj);

j=1;

%Preallocate the frame structure

Frame=struct('cdata',1,'colormap',cell([1 100]));

                                 INPUT VIDEO

 

%Get the first frame as image

%Add text

%Use 'getframe' to grab the figure

Caption={'How to add Caption/Subtitles';'to video in MATLAB';'GET CODE AT http://angeljohnsy.blogspot.com/';};

I=A(:,:,:,1);

imshow(I),hold on

text(80,100,Caption{1},'Color','w','FontWeight','Bold','FontSize',30);

text(150,200,Caption{2},'Color','w','FontWeight','Bold','FontSize',30);

text(300,480,Caption{3},'Color','r','FontWeight','Bold','FontSize',15);

Frame(j:j+9)=getframe;

j=j+10;

%Get the Second frame as an image i.eA(:,:,:,2);

%Add the Poem title and the author name

Title_={'THE ROAD NOT TAKEN';'-ROBERT FROST'};

I=A(:,:,:,2);

imshow(I), hold on

text(40,100,Title_{1},'Color','k','FontWeight','Bold','FontSize',40);

text(350,550,Title_{2},'Color','k','FontWeight','Bold','FontSize',30);

Frame(j:j+9)=getframe;

j=j+10;

%Create a cell array with the Poem versus

Txt={'TWO roads diverged in a yellow wood,';

'And sorry I could not travel both';

'And be one traveler, long I stood';

'And looked down one as far as I could';   

'To where it bent in the undergrowth;';

'Then took the other, as just as fair,';   

'And having perhaps the better claim,';

'Because it was grassy and wanted wear;';  

'Though as for that the passing there';

'Had worn them really about the same,';

'And both that morning equally lay';   

'In leaves no step had trodden black.';

'Oh, I kept the first for another day!';   

'Yet knowing how way leads on to way,';

'I doubted if I should ever come back.';

'I shall be telling this with a sigh'; 

'Somewhere ages and ages hence:';  

'Two roads diverged in a wood, and I—';

'I took the one less traveled by,';

'And that has made all the difference.';};

%display the image

%Add the poem lines

%Grab the frame

%There are 20 lines totally

%Add 3 and 2 lines alternatively in each frame

    inc=0;

for i=3:size(A,4)

   

    n=mod(i,2);  

    I=A(:,:,:,i);

   

    imshow(I), hold on

for k=1:2+n

    text(80,440+(k*40),Txt{k+inc},'Color','w','FontWeight','Bold','FontSize',25);

   

end

    inc=inc+2+n;

    Frame(j:j+19)=getframe;

    j=j+20;

 end

Create a Video File:

obj=avifile('Road Not Taken.avi','FPS',3);

 obj=addframe(obj,Frame);

obj=close(obj);

                            VIDEO WITH  SUBTITLE

Explanation:

       text(40,100,Title_{1},'Color','k','FontWeight','Bold','FontSize',40);

                This code will add the text ‘THE ROAD NOT TAKEN’ with color font size 40, font weight bold and color black (k).

          

How to get frames from a video

MATLAB CODE to get images from video:
To extract frames from a video.

              Frames can be obtained from a video and converted into images. To convert a video frame into an image, the MATLAB function ‘frame2im’ is used.  

                                      To read a video in avi format, the function ‘aviread’ is used.  The original format of the video that I am using as an example is .gif file format. I converted the .gif file format image into an avi format video. Learn how to convert a gif image into a video...

 For instance, in the ‘fun.avi’ video I am interested in the frame number 58. So I am converting the 58^th frame into an image.

MATLAB CODE:

%How to get frames from a video

mov=aviread('fun.avi');

Im=frame2im(mov(1,58));

figure,imshow(Im);

Frame 58

The above process can be done using 'mmreader' function also.


MATLAB CODE:


Vobj=mmreader('fun.avi');

Im=read(Vobj,58);
imshow(Im);

After playing the video, I thought of modifying some frames. So I converted the frames from 58 to 64 into images and added a smiley to the images by performing image arithmetic operations.

Then I converted those images into frames and saved as a video file in ‘smiley.avi’.

Lmov=aviread('smiley.avi');

MIm=frame2im(Lmov(1,1));

figure,imshow(MIm);

Modified Frame 58

%Preallocating the structure array

frame=struct('cdata',1,'colormap',cell([1 91]));

I added the modified frames to the original video.

%Modify the video in the middle

frame(1,1:57)=mov(1,1:57);

frame(1,58:87)=Lmov(1,1:30);

frame(1,88:91)=mov(1,64:67);

implay(frame,5);

  If we are interested in playing only some of the frames in the original video then, we can view those frames alone. Here I am interested in viewing the frames from 27 to 33.

%Part of the video

scz=figure;

set(scz, 'position', [300 100  size(Im,1)+130 size(Im,2)-100]);

FRange=[1 27:33];

%Here 1 is for the number of times the video has to be repeated

%27:33 indicates the frames from 27 to 33.

movie(scz,mov,FRange,5);

We can also save the desired frames into a file. An avifile object is created with the file name ‘VidPart.avi’. Then the desired frames from 27 to 33 are added by using the syntax ‘addframe’.

%To save the desired part alone

obj=avifile('VidPart.avi','FPS',5);

obj=addframe(obj,mov(27:33));

obj=close(obj);

How to create Video from still image

                  Using a single JPEG image, we can create image sequences.  To create image sequences, we need to convert the image into frame. The matlab function   ‘im2frame’ is used to create frame from an image. In this example, I took an image and created some frames by performing rotation operation on that image.

                             Initially, I pre allocated a structure array.  When the function ‘im2frame’ is used on an image, a frame is created.  The frame is a structure that contains the cdata and the colormap.

Example:

I=imread(‘ball.jpg’);

frame(1)=im2frame(I);

frame(1)

ans =

       cdata: [323x400x3 uint8]

      colormap: []

After allocating the space for the frames, I rotated the image from 1 to 360 degrees with the interval of 10 degrees.  36 frames will be obtained.

During each rotation operation, the size of the image will be modified. So, I resized the image to the original size after every rotation.

MATLAB CODE:

%Create a video from still image

I=imread('ball.jpg');

m=size(I,1);

n=size(I,2);

j=1;

%Preallocate the structure array

%The fields are 'cdata' and 'colormap'

%The size should be 1xm

frame=struct('cdata',1,'colormap',cell([1 36]));

for i=1:10:360

    %Rotate the image

    Im=imrotate(I,i);

    %To convert an image to frame use the function 'im2frame'.

    frame(j)=im2frame(imresize(Im,[m n]));

j=j+1;

end

%scz=figure;

%set(scz, 'position', [300 100  size(I,1)+200 size(I,2)]);

%movie(scz ,frame,1,30);

%Play the image sequence with fps=10.

implay(frame,10);

We can either use ‘movie’ function or ‘implay’ function to play the video.

Function: movie

If the ‘movie’ function is used. Then we can specify the window size and the position.

%movie(scz ,frame,N,FPS);

N-number of times

FPS-Frames per second

Function :  implay

It can take two parameters, frames and the FPS.