VideoWriter

Objective-C

@interface VideoWriter : NSObject

Swift

class VideoWriter : NSObject

Video writer class.

The class provides C++ API for writing video files or image sequences.

Member of Videoio

Methods

  •  The `apiPreference` parameter allows to specify API backends to use. Can be used to enforce a specific reader implementation
 if multiple are available: e.g. cv::CAP_FFMPEG or cv::CAP_GSTREAMER.

    Declaration

    Objective-C

    - (nonnull instancetype)initWithFilename:(nonnull NSString *)filename
                           apiPreference:(int)apiPreference
                                  fourcc:(int)fourcc
                                     fps:(double)fps
                               frameSize:(nonnull Size2i *)frameSize
                                 isColor:(BOOL)isColor;

    Swift

    init(filename: String, apiPreference: Int32, fourcc: Int32, fps: Double, frameSize: Size2i, isColor: Bool)
  •  The `apiPreference` parameter allows to specify API backends to use. Can be used to enforce a specific reader implementation
 if multiple are available: e.g. cv::CAP_FFMPEG or cv::CAP_GSTREAMER.

    Declaration

    Objective-C

    - (nonnull instancetype)initWithFilename:(nonnull NSString *)filename
                           apiPreference:(int)apiPreference
                                  fourcc:(int)fourcc
                                     fps:(double)fps
                               frameSize:(nonnull Size2i *)frameSize;

    Swift

    init(filename: String, apiPreference: Int32, fourcc: Int32, fps: Double, frameSize: Size2i)

  • Declaration

    Objective-C

    - (instancetype)initWithFilename:(NSString*)filename apiPreference:(int)apiPreference fourcc:(int)fourcc fps:(double)fps frameSize:(Size2i*)frameSize params:(IntVector*)params;

    Swift

    init(filename: String, apiPreference: Int32, fourcc: Int32, fps: Double, frameSize: Size2i, params: IntVector)

  • Declaration

    Objective-C

    - (nonnull instancetype)initWithFilename:(nonnull NSString *)filename
                                  fourcc:(int)fourcc
                                     fps:(double)fps
                               frameSize:(nonnull Size2i *)frameSize
                                 isColor:(BOOL)isColor;

    Swift

    init(filename: String, fourcc: Int32, fps: Double, frameSize: Size2i, isColor: Bool)

    Parameters

    filename

    Name of the output video file.
    fourcc

    4-character code of codec used to compress the frames. For example, VideoWriter::fourcc(‘P’,‘I’,‘M’,‘1’) is a MPEG-1 codec, VideoWriter::fourcc(‘M’,‘J’,‘P’,‘G’) is a motion-jpeg codec etc. List of codes can be obtained at Video Codecs by FOURCC page. FFMPEG backend with MP4 container natively uses other values as fourcc code: see ObjectType, so you may receive a warning message from OpenCV about fourcc code conversion.
    fps

    Framerate of the created video stream.
    frameSize

    Size of the video frames.
    isColor

    If it is not zero, the encoder will expect and encode color frames, otherwise it will work with grayscale frames.

    @b Tips:

    • With some backends fourcc=-1 pops up the codec selection dialog from the system.
    • To save image sequence use a proper filename (eg. img_%02d.jpg) and fourcc=0 OR fps=0. Use uncompressed image format (eg. img_%02d.BMP) to save raw frames.
    • Most codecs are lossy. If you want lossless video file you need to use a lossless codecs (eg. FFMPEG FFV1, Huffman HFYU, Lagarith LAGS, etc…)
    • If FFMPEG is enabled, using codec=0; fps=0; you can create an uncompressed (raw) video file.

  • Declaration

    Objective-C

    - (nonnull instancetype)initWithFilename:(nonnull NSString *)filename
                                  fourcc:(int)fourcc
                                     fps:(double)fps
                               frameSize:(nonnull Size2i *)frameSize;

    Swift

    init(filename: String, fourcc: Int32, fps: Double, frameSize: Size2i)

    Parameters

    filename

    Name of the output video file.
    fourcc

    4-character code of codec used to compress the frames. For example, VideoWriter::fourcc(‘P’,‘I’,‘M’,‘1’) is a MPEG-1 codec, VideoWriter::fourcc(‘M’,‘J’,‘P’,‘G’) is a motion-jpeg codec etc. List of codes can be obtained at Video Codecs by FOURCC page. FFMPEG backend with MP4 container natively uses other values as fourcc code: see ObjectType, so you may receive a warning message from OpenCV about fourcc code conversion.
    fps

    Framerate of the created video stream.
    frameSize

    Size of the video frames. will work with grayscale frames.

    @b Tips:

    • With some backends fourcc=-1 pops up the codec selection dialog from the system.
    • To save image sequence use a proper filename (eg. img_%02d.jpg) and fourcc=0 OR fps=0. Use uncompressed image format (eg. img_%02d.BMP) to save raw frames.
    • Most codecs are lossy. If you want lossless video file you need to use a lossless codecs (eg. FFMPEG FFV1, Huffman HFYU, Lagarith LAGS, etc…)
    • If FFMPEG is enabled, using codec=0; fps=0; you can create an uncompressed (raw) video file.

  • The params parameter allows to specify extra encoder parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, … .) see cv::VideoWriterProperties

    Declaration

    Objective-C

    - (nonnull instancetype)initWithFilename:(nonnull NSString *)filename
                                  fourcc:(int)fourcc
                                     fps:(double)fps
                               frameSize:(nonnull Size2i *)frameSize
                                  params:(nonnull IntVector *)params;

    Swift

    init(filename: String, fourcc: Int32, fps: Double, frameSize: Size2i, params: IntVector)

  • Default constructors

     The constructors/functions initialize video writers.
 -   On Linux FFMPEG is used to write videos;
 -   On Windows FFMPEG or MSWF or DSHOW is used;
 -   On MacOSX AVFoundation is used.

    Declaration

    Objective-C

    - (nonnull instancetype)init;

    Swift

    init()

  • Returns used backend API name

      - note: Stream should be opened.

    Declaration

    Objective-C

    - (nonnull NSString *)getBackendName;

    Swift

    func getBackendName() -> String

  • Returns true if video writer has been successfully initialized.

    Declaration

    Objective-C

    - (BOOL)isOpened;

    Swift

    func isOpened() -> Bool

  • Declaration

    Objective-C

    - (BOOL)open:(NSString*)filename apiPreference:(int)apiPreference fourcc:(int)fourcc fps:(double)fps frameSize:(Size2i*)frameSize isColor:(BOOL)isColor NS_SWIFT_NAME(open(filename:apiPreference:fourcc:fps:frameSize:isColor:));

    Swift

    func open(filename: String, apiPreference: Int32, fourcc: Int32, fps: Double, frameSize: Size2i, isColor: Bool) -> Bool

  • Declaration

    Objective-C

    - (BOOL)open:(NSString*)filename apiPreference:(int)apiPreference fourcc:(int)fourcc fps:(double)fps frameSize:(Size2i*)frameSize NS_SWIFT_NAME(open(filename:apiPreference:fourcc:fps:frameSize:));

    Swift

    func open(filename: String, apiPreference: Int32, fourcc: Int32, fps: Double, frameSize: Size2i) -> Bool

  • Declaration

    Objective-C

    - (BOOL)open:(NSString*)filename apiPreference:(int)apiPreference fourcc:(int)fourcc fps:(double)fps frameSize:(Size2i*)frameSize params:(IntVector*)params NS_SWIFT_NAME(open(filename:apiPreference:fourcc:fps:frameSize:params:));

    Swift

    func open(filename: String, apiPreference: Int32, fourcc: Int32, fps: Double, frameSize: Size2i, params: IntVector) -> Bool

  • Initializes or reinitializes video writer.

     The method opens video writer. Parameters are the same as in the constructor
 VideoWriter::VideoWriter.
 - returns: `true` if video writer has been successfully initialized

 The method first calls VideoWriter::release to close the already opened file.

    Declaration

    Objective-C

    - (BOOL)open:(nonnull NSString *)filename
       fourcc:(int)fourcc
          fps:(double)fps
    frameSize:(nonnull Size2i *)frameSize
      isColor:(BOOL)isColor;

    Swift

    func open(filename: String, fourcc: Int32, fps: Double, frameSize: Size2i, isColor: Bool) -> Bool

  • Initializes or reinitializes video writer.

     The method opens video writer. Parameters are the same as in the constructor
 VideoWriter::VideoWriter.
 - returns: `true` if video writer has been successfully initialized

 The method first calls VideoWriter::release to close the already opened file.

    Declaration

    Objective-C

    - (BOOL)open:(nonnull NSString *)filename
       fourcc:(int)fourcc
          fps:(double)fps
    frameSize:(nonnull Size2i *)frameSize;

    Swift

    func open(filename: String, fourcc: Int32, fps: Double, frameSize: Size2i) -> Bool

  • Declaration

    Objective-C

    - (BOOL)open:(NSString*)filename fourcc:(int)fourcc fps:(double)fps frameSize:(Size2i*)frameSize params:(IntVector*)params NS_SWIFT_NAME(open(filename:fourcc:fps:frameSize:params:));

    Swift

    func open(filename: String, fourcc: Int32, fps: Double, frameSize: Size2i, params: IntVector) -> Bool

  • Sets a property in the VideoWriter.

    Declaration

    Objective-C

    - (BOOL)set:(int)propId value:(double)value;

    Swift

    func set(propId: Int32, value: Double) -> Bool

    Parameters

    propId

    Property identifier from cv::VideoWriterProperties (eg. cv::VIDEOWRITER_PROP_QUALITY) or one of REF: videoio_flags_others
    value

    Value of the property.

    Return Value

    true if the property is supported by the backend used by the VideoWriter instance.

  • Returns the specified VideoWriter property

    Declaration

    Objective-C

    - (double)get:(int)propId;

    Swift

    func get(propId: Int32) -> Double

    Parameters

    propId

    Property identifier from cv::VideoWriterProperties (eg. cv::VIDEOWRITER_PROP_QUALITY) or one of REF: videoio_flags_others

    Return Value

    Value for the specified property. Value 0 is returned when querying a property that is not supported by the backend used by the VideoWriter instance.

  • Concatenates 4 chars to a fourcc code

     - returns: a fourcc code

 This static method constructs the fourcc code of the codec to be used in the constructor
 VideoWriter::VideoWriter or VideoWriter::open.

    Declaration

    Objective-C

    + (int)fourcc:(char)c1 c2:(char)c2 c3:(char)c3 c4:(char)c4;

    Swift

    class func fourcc(c1: Int8, c2: Int8, c3: Int8, c4: Int8) -> Int32

  • Writes the next video frame

    Declaration

    Objective-C

    - (void)write:(nonnull Mat *)image;

    Swift

    func write(image: Mat)

    Parameters

    image

    The written frame. In general, color images are expected in BGR format.

    The function/method writes the specified image to video file. It must have the same size as has been specified when opening the video writer.