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read - Class: mmreader

Read video frame data from multimedia reader object

Syntax

video = read(obj) video = read(obj, index)

Description

video = read(obj) reads in all video frames from the file associated with obj.

video = read(obj, index) reads only the specified frames. index can be a single number or a two-element array representing an index range of the video stream.

Input Arguments

obj

Name of multimedia object created with mmreader.

index

Frames to read, where the first frame number is 1. Use Inf to represent the last frame of the file.

For example:

video = read(obj, 1);         % first frame only
video = read(obj, [1 10]);    % first 10 frames
video = read(obj, Inf);       % last frame only
video = read(obj, [50 Inf]);  % frame 50 thru end

MATLAB cannot determine the number of frames in a variable frame rate file until you read the last frame. If the requested index extends beyond the end of the file, read returns either a warning or an error. For more information, see Reading Variable Frame Rate Video in the MATLAB Data Import and Export documentation.

Default: [1 Inf]

Output Arguments

video

Array of uint8 data representing RGB24 video frames. The dimensions are H-by-W-by-B-by-F, where:

H Image frame height.

W Image frame width.

B Number of bands in the image (for example, 3 for RGB).

F Number of frames read.

Example

Read and play back the movie file xylophone.mpg:

xyloObj = mmreader('xylophone.mpg');

nFrames = xyloObj.NumberOfFrames;
vidHeight = xyloObj.Height;
vidWidth = xyloObj.Width;

% Preallocate movie structure.
mov(1:nFrames) = ...
    struct('cdata', zeros(vidHeight, vidWidth, 3, 'uint8'),...
           'colormap', []);

% Read one frame at a time.
for k = 1 : nFrames
    mov(k).cdata = read(xyloObj, k);
end

% Size a figure based on the video's width and height.
hf = figure;
set(hf, 'position', [150 150 vidWidth vidHeight])

% Play back the movie once at the video's frame rate.
movie(hf, mov, 1, xyloObj.FrameRate);