VideoWriter

Write video files

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Description

VideoWriter objects allow you to create video files from arrays or MATLAB® movies.

You can use the VideoWriter function with a predefined profile to create a VideoWriter object with properties tailored to a specific format, such as 'Uncompressed AVI' or 'MPEG-4'. After you create the object, you can use dot notation to view or modify a particular property:

v = VideoWriter('newfile.mj2','Motion JPEG 2000');
v.CompressionRatio = 3;

Modify property values before opening the video file for writing. After you call the open function, you cannot change the value of a property.

Create Object

Create VideoWriter objects using the VideoWriter function.

Properties

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This property is read only.

Number of color channels in each output video frame, specified as a positive integer:

  • Uncompressed AVI, Motion JPEG AVI, and MPEG-4 files have three color channels.

  • Indexed and grayscale AVI files have one color channel.

  • For Motion JPEG 2000 files, the number of channels depends on the input data to the writeVideo function: one for monochrome image data, three for color data.

Data Types: double

Color information for video file, specified as a numeric matrix with three columns and a maximum of 256 rows. Each row in the matrix defines one color using an RGB triplet. An RGB triplet is a three-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can set the colormap explicitly before the call to open, or by using the colormap field of a movie frame structure at the time of writing the first frame.

The Colormap property only applies to objects used for writing indexed AVI files.

Example: colormap(summer(256))

Data Types: double | uint8

Target compression ratio, specified as an integer greater than 1. The compression ratio is the ratio between the number of bytes in the input image and the number of bytes in the compressed image. The video data is compressed as much as possible, up to the specified target.

CompressionRatio is available only for objects used for writing Motion JPEG 2000 files. After you call open, you cannot change the CompressionRatio value. If you previously set LosslessCompression to true, setting CompressionRatio generates an error.

Example: 5

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

This property is read only.

Duration of the output file in seconds, specified as a scalar value.

Data Types: double

This property is read only.

Type of file to write, specified as 'avi', 'mp4', or 'mj2'.

This property is read only.

Name of file, specified as a character vector.

Data Types: char

This property is read only.

Number of frames written to the video file, specified as an integer.

Data Types: double

Rate of video playback in frames per second, specified as a positive number.

After you call open, you cannot change the FrameRate value.

Example: 10

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

This property is read only.

Height of each video frame in pixels, specified as a scalar. The writeVideo method sets values for Height and Width based on the dimensions of the first frame.

MPEG-4 files require frame dimensions that are divisible by two. If the input frame height for an MPEG-4 file is not an even number, VideoWriter pads the frame with a row of black pixels at the bottom. For MPEG-4 files on Windows® systems, the allowed value depends on the version of Windows. For example, on Windows 10 the allowed Height is in the range [34,2160].

Data Types: double

Lossless compression, specified as true or false. The LosslessCompression property is only available for objects used for writing Motion JPEG 2000 files.

If LosslessCompression is true, then:

  • The writeVideo function writes data so that the decompressed data is identical to the input data.

  • VideoWriter ignores any specified value for CompressionRatio.

After you call open, you cannot change the LosslessCompression value.

By default, LosslessCompression is false for the 'Motion JPEG 2000' profile and true for the 'Archival' profile.

Data Types: logical

Bit depth for Motion JPEG 2000 files, specified as an integer in the range [1,16]. The bit depth is the number of least-significant bits in the input image data

MJ2BitDepth is available only for objects used for writing Motion JPEG 2000 files. If you do not specify a value before calling the open method, VideoWriter sets the bit depth based on the input data type. For example, if the input data to writeVideo is an array of uint8 or int8 values, then MJ2BitDepth is 8.

Example: 8

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

This property is read only.

Full path to the video file, specified as a character vector.

Data Types: char

Video quality, specified as an integer in the range, [0,100]. Higher quality numbers result in higher video quality and larger file sizes. Lower quality numbers result in lower video quality and smaller file sizes.

Quality is available only for objects associated with the MPEG-4 or Motion JPEG AVI profile. After you call open, you cannot change the Quality value.

Example: 50

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

This property is read only.

Number of bits per pixel in each output video frame, specified as a numeric scalar.

AVI files with truecolor video, Motion JPEG AVI, and MPEG-4 files have 24 bits per pixel (8 bits for each of three color bands).

Indexed and grayscale AVI files have 8 bits per pixel.

For Motion JPEG 2000 files, the number of bits per pixel depends on the value of MJ2BitDepth and the number of bands of image data. For example, if the input data to writeVideo is a three-dimensional array of uint16 or int16 values, the default value of MJ2BitDepth is 16, and VideoBitsPerPixel is 48 (three times the bit depth).

Data Types: double

This property is read only.

Type of video compression, specified as 'None', 'H.264', 'Motion JPEG', or 'Motion JPEG 2000'.

Data Types: char

This property is read only.

MATLAB representation of the video format, specified as a character vector.

For file types other than Motion JPEG 2000 files, VideoFormat is one of the following.

Video Format

Value of VideoFormat

Uncompressed AVI, Motion JPEG AVI, or MPEG-4 files

'RGB24'

AVI files with indexed video

'Indexed'

AVI files with grayscale video

'Grayscale'

For Motion JPEG 2000 files, VideoFormat depends on the value of MJ2BitDepth and the format of the input image data to the writeVideo method. For example, if you do not specify the MJ2BitDepth property, VideoWriter sets the format as shown in this table.

Format of Image Data

Value of VideoFormat

Single-band uint8'Mono8'
Single-band int8'Mono8 Signed'
Single-band uint16'Mono16'
Single-band int16'Mono16 Signed'
Three-banded uint8'RGB24'
Three-banded int8'RGB24 Signed'
Three-banded uint16'RGB48'
Three-banded int16'RGB48 Signed'

This property is read only.

Width of each video frame in pixels, specified as a numeric scalar. The writeVideo function sets values for Height and Width based on the dimensions of the first frame.

MPEG-4 files require frame dimensions that are divisible by two. If the input frame width for an MPEG-4 file is not an even number, then VideoWriter pads the frame with a column of black pixels along the right side. For MPEG-4 files on Windows systems, the allowed value depends on the version of Windows. For example, on Windows 10 the allowed Width is in the range [34,3872].

Data Types: double

Object Functions

open Open file for writing video data
close Close file after writing video data
writeVideo Write video data to file
VideoWriter.getProfiles Profiles and file formats that VideoWriter supports

Examples

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Open Script

Create a VideoWriter object to write a Motion JPEG AVI file named newfile.avi.

v = VideoWriter('newfile.avi');

Open the file for writing and write a 300-by-300 matrix of data to the file.

open(v)
writeVideo(v,rand(300))

Close the file.

close(v)
Open Script

Create an array containing data from the sample still image, peppers.png.

A = imread('peppers.png');

Create a VideoWriter object for a new uncompressed AVI file for RGB24 video.

v = VideoWriter('newfile.avi','Uncompressed AVI');

Open the file for writing.

open(v)

Write the image in A to the video file.

writeVideo(v,A)

Close the file.

close(v)

Write a sequence of frames to a compressed AVI file named peaks.avi.

Prepare the new file.

v = VideoWriter('peaks.avi');
open(v);

Generate initial data and set axes and figure properties.

Z = peaks;
surf(Z); 
axis tight manual 
set(gca,'nextplot','replacechildren');

Create a set of frames and write each frame to the file.

for k = 1:20 
   surf(sin(2*pi*k/20)*Z,Z)
   frame = getframe;
   writeVideo(v,frame);
end

close(v);

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Introduced in R2010b

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