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Handling videos in MATLAB
Note: MATLAB supports only raw (uncompressed) avi files on Linux
and only some
Indeo and Cinepack compressed versions on Windows. But mostly
you get videos in
MPEG. So you need to convert to raw or any supported format. For
this, FFmpeg can be
used (see Section 2).
Note: Avi means Audio Video Interleave and is only a container
format. Avi does not
mean raw video. It is possible to have mpeg or many other
compressed avi files.
MATLAB can not read such a compressed avi files. (See
http://en.wikipedia.org/wiki/Audio_Video_Interleave).
/****************************************/
Section 1
If you have raw video
/***************************************/
If you have raw video, then handling in MATLAB is quite easy.
You need to usefunctions avifile, aviread, frame2im, im2frame and
addframe functions.
Following code converts given video (in.avi) to QVGA (320x240)
resolution video
(out.avi). This example shows how to use video related functions
in MATLAB. For
further details and other functions see MATLAB help.
/***************************************/
% Example to scale a given video to QVGA (320x240) resolutionfin
= 'e:\in.avi';fout = 'd:\out.avi';
fileinfo = aviinfo(fin);nframes = fileinfo.NumFrames;
aviobj = avifile(fout, 'compression', 'none', 'fps',
fileinfo.FramesPerSecond);
for i = 1:nframes%Read frames from input videomov_in =
aviread(fin,i);im_in = frame2im(mov_in);
%Do processing on each frame of the video%In this example -
scaling
[ht wd ch] = size(im_in);im_out = imresize(im_in, [240 320],
'bilinear');
%Write frames to output videofrm = im2frame(im_out);aviobj =
addframe(aviobj,frm);
i %Just to display frame numberend;%Don't forget to close output
fileaviobj = close(aviobj);
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return;
/***************************************/
/****************************************/
Section 2
If you have compressed video
/***************************************/
You can use any converter tool to convert compressed video to
uncompressed avi format.
One such tool is FFmpeg (http://ffmpeg.mplayerhq.hu/index.html).
Mplayer, VLC and
many other players are based on this codec.
If you are a Windows user, just download latest binary from
http://ffdshow.faireal.net/mirror/ffmpeg/ (Any virus? I dont
know. Download at your
risk!).
(You can use WinRAR to uncompress .7z -
http://www.freedownloadscenter.com/Utilities/Compression_and_Zip_File_Utilities/Win
RAR_Download.html)
Use this command to convert any compressed file (compressed.any)
to uncompressed avi
file (uncompressed.avi) (Note: pthreadGC2.dll file should be in
the same directory as
ffmpeg.exe).
ffmpeg.exe -i compressed.any -vcodec rawvideo
uncompressed.avi
This should work most of the cases. However, sometimes it may
not work (because, avi
is a container format by Microsoft! :)). The converted video may
have only blank frames
or MATLAB may not be able to read it properly. In such a case,
you can try steps
explained in Section 3.
/****************************************/
Section 3
If you have compressed video and
Steps in Section 2 does not work
/***************************************/
Create a folder by name images
Use this command to convert each frame of the compressed video
to bmp (or ppm)
images and put it into the folder images.
ffmpeg.exe -i compressed.any images/image_%d.bmp
Now you can use these images for processing. If you want
uncompressed avi file, then
use following MATLAB code to combine all raw images into a
single uncompressed avi
file.
/***************************************/
%Script file to combine images to an uncompressed avi
file%Directory that contains images
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in_dir = 'Q:\temp\ffmpeg.rev11870\images\';
fout = 'q:\out1.avi'; %Output file namenum_images = 341; %Number
of images
%Set a suitable frame rate fpsaviobj = avifile(fout,
'compression', 'none', 'fps', 25);
for i = 1:num_images;temp = sprintf('%d', i);name = [in_dir,
'image_', temp, '.bmp']; %For ppm, changeimg = imread(name);frm =
im2frame(img);aviobj = addframe(aviobj,frm);
iend;
aviobj = close(aviobj);return;
Any feedback? Mail to paresh.kalyan and kv.kirans at gmail
