Read Video Files

Read Frames Beginning at Specified Time or Frame Index

Read part of a video file starting 0.5 second from the beginning of the file. Then, read the video starting from frame index 100 to the end of the video file.

Create a VideoReader object for the sample video file xylophone_video.mp4.

vidObj = VideoReader("xylophone_video.mp4");

Specify that reading should begin 0.5 second from the beginning of the file by setting the CurrentTime property.

vidObj.CurrentTime = 0.5;

Read video frames until the end of the file by using the readFrame method.

while hasFrame(vidObj)
    vidFrame = readFrame(vidObj);
    imshow(vidFrame)
    pause(1/vidObj.FrameRate)
end

Alternatively, you can read frames from a video starting at a specified frame index to the end of the video by using the read method. Specify the indices to read as [100 Inf]. The read method returns all the frames starting at 100 to the end of the video file.

vidframes = read(vidObj,[100 Inf]);

Clear the VideoReader object.

clear vidObj

Read Frames Within Specified Interval

Read a part of a video file by specifying the time or frame interval.

Read the video frames between 0.6 and 0.9 seconds. First, create a VideoReader object and a structure array to hold the frames.

vidObj = VideoReader("xylophone_video.mp4");
s = struct("cdata",zeros(vidObj.Height,vidObj.Width,3,"uint8"),colormap=[]);

Then specify that reading should begin 0.6 second from the beginning of the file by setting the CurrentTime property.

vidObj.CurrentTime = 0.6;

Read one frame at a time until CurrentTime reaches 0.9 second. Append data from each video frame to the structure array. View the number of frames in the structure array. s is a 1-by-10 structure array indicating that 10 frames were read. For information on displaying the frames in the structure array s as a movie, see the movie function reference page.

k = 1;
while vidObj.CurrentTime <= 0.9
    s(k).cdata = readFrame(vidObj);
    k = k+1;
end
whos s

  Name      Size              Bytes  Class     Attributes

  s         1x10            2305437  struct              

Alternatively, you can read all the frames in a specified interval by using frame indices. For example, specify the range of frames to read as [18 27]. The read method returns an m-by-n-by-p-by-10 array (where each frame has size m-by-n-by-p), which indicates that 10 frames were read.

frames = read(vidObj,[18 27]);
whos frames

  Name          Size                    Bytes  Class    Attributes

  frames      240x320x3x10            2304000  uint8              

Clear the VideoReader object.

clear vidObj

Read All Frames

Read all the frames from the video, one frame at a time or all of the frames at once.

Create a VideoReader object and display the total number of frames in the video.

vidObj = VideoReader("xylophone_video.mp4");
vidObj.NumFrames

ans = 
141

Read all of the frames, one frame at a time, by using the readFrame method, and display the frames.

while hasFrame(vidObj)
   frame = readFrame(vidObj);
   imshow(frame)
   pause(1/vidObj.FrameRate)
end

Alternatively, you can read all the video frames at once. The read method returns an m-by-n-by-p-by-141 array (where each frame has size m-by-n-by-p) of video frames.

allFrames = read(vidObj);
whos allFrames

  Name             Size                      Bytes  Class    Attributes

  allFrames      240x320x3x141            32486400  uint8              

Clear the VideoReader object.

clear vidObj

Troubleshooting and Tips for Video Reading