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mmreader - Create multimedia reader object for reading video files

Syntax

obj = mmreader(filename) obj = mmreader(filename, 'P1', V1, 'P2', V2,...)

Description

obj = mmreader(filename) constructs a multimedia reader object, obj, that can read video data from a multimedia file named filename. The mmreader function searches for the file on the MATLAB path, and generates an error if it cannot construct the object for any reason.

mmreader supports the following file formats:

Platform	Supported File Formats
Windows, Macintosh, and Linux	Motion JPEG 2000 (`.mj2`)
Windows	AVI (`.avi`), MPEG-1 (`.mpg`), Windows Media Video (`.wmv`, `.asf`, `.asx`), and any format supported by Microsoft DirectShow.
Macintosh	AVI (`.avi`), MPEG-1 (`.mpg`), MPEG-4 (`.mp4`, `.m4v`), Apple QuickTime Movie (`.mov`), and any format supported by QuickTime as listed on http://www.apple.com/quicktime/player/specs.html.
Linux	Any format supported by your installed plug-ins for GStreamer 0.10 or above, as listed on http://gstreamer.freedesktop.org/documentation/plugins.html, including AVI (`.avi`) and Ogg Theora (`.ogg`).

There are no restrictions on file extensions. For more information, see Supported Video File Formats in the MATLAB Data Import and Export documentation

obj = mmreader(filename, 'P1', V1, 'P2', V2,...) constructs a multimedia object and assigns values V1, V2, etc. to the respective specified properties P1, P2, etc. If you specify an invalid property name or property value, MATLAB throws an error and does not create the object. Property value pairs can be in any format supported by the set function: parameter-value string pairs, structures, or parameter-value cell array pairs. The mmreader object supports the following properties:

Property	Description	Read-Only	Default Value
`BitsPerPixel`	Bits per pixel of the video data	Yes
`Duration`	Total length of file in seconds	Yes
`FrameRate`	Frame rate of the video in frames per second	Yes
`Height`	Height of the video frame in pixels	Yes
`Name`	Name of the file from which the reader object was created	Yes
`NumberOfFrames`	Total number of frames in the video stream	Yes
`Path`	String containing the full path to the file associated with the reader	Yes
`Tag`	Generic string for you to set	No	`''`
`Type`	Class name of the object	Yes	`mmreader`
`UserData`	Generic field for any user-defined data	No	`[]`
`VideoFormat`	String indicating the video format as it is represented in MATLAB, e.g., `RGB24`	Yes
`Width`	Width of the video frame in pixels	Yes

Remarks

Some files store video at a variable frame rate, including many Windows Media Video files. For these files, mmreader cannot determine the number of frames until you read the last frame. When you construct the object, mmreader returns a warning and does not set the NumberOfFrames property.

To count the number of frames in a variable frame rate file, call the read function to read the last frame of the file. For example:

vidObj = mmreader('varFrameRateFile.wmv');
lastFrame = read(vidObj, inf);
numFrames = vidObj.NumberOfFrames;

Because mmreader must decode all video data to count the frames reliably, the call to read sometimes takes a long time to run. For more information, see Reading Variable Frame Rate Video in the MATLAB Data Import and Export documentation.

Examples

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);

mmreader - Create multimedia reader object for reading video files

Syntax

Description

Remarks

Examples

See Also

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