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Video Reading

Note: Reading of audio streams is not yet implemented

Reading Video Files

VideoIO contains a simple high-level interface which allows reading of video frames from a supported video file (or from a camera device, shown later).

The simplest form will load the entire video into memory as a vector of image arrays.

using VideoIO
VideoIO.load("video.mp4")
VideoIO.load

Frames can be read sequentially until the end of the file:

using VideoIO

# Construct a AVInput object to access the video and audio streams in a video container
# io = VideoIO.open(video_file)
io = VideoIO.testvideo("annie_oakley") # for testing purposes

# Access the video stream in an AVInput, and return a VideoReader object:
f = VideoIO.openvideo(io) # you can also use a file name, instead of a AVInput

img = read(f)

while !eof(f)
    read!(f, img)
    # Do something with frames
end
close(f)
VideoIO.openvideo

Alternatively, you can open the video stream in a file directly with VideoIO.openvideo(filename), without making an intermediate AVInput object, if you only need the video.

VideoIO also provides an iterator interface for VideoReader, which behaves like other mutable iterators in Julia (e.g. Channels). If iteration is stopped early, for example with a break statement, then it can be resumed in the same spot by iterating on the same VideoReader object. Consequently, if you have already iterated over all the frames of a VideoReader object, then it will be empty for further iteration unless its position in the video is changed with seek.

using VideoIO

f = VideoIO.openvideo("video.mp4")
for img in f
    # Do something with img
end
# Alternatively use collect(f) to get all of the frames

# Further iteration will show that f is now empty
@assert isempty(f)

close(f)

Seeking through the video can be achieved via seek(f, seconds::Float64) and seekstart(f) to return to the start.

VideoIO.seek

VideoIO.seekstart

Frames can be skipped without reading frame content via skipframe(f) and skipframes(f, n)

VideoIO.skipframe

VideoIO.skipframes

Total available frame count is available via counttotalframes(f)

VideoIO.counttotalframes

!!! note H264 videos encoded with crf>0 have been observed to have 4-fewer frames available for reading.

Changing the target pixel format for reading

It can be helpful to be explicit in which pixel format you wish to read frames as. Here a grayscale video is read and parsed into a Vector(Array{UInt8}}

f = VideoIO.openvideo(filename, target_format=VideoIO.AV_PIX_FMT_GRAY8)

while !eof(f)
    img = reinterpret(UInt8, read(f))
end
close(f)

Reading Camera Output

Frames can be read iteratively

using VideoIO
cam = VideoIO.opencamera()
fps = VideoIO.framerate(cam)
for i in 1:100
    img = read(cam)
    sleep(1/fps)
end

To change settings such as the frame rate or resolution of the captured frames, set the appropriate value in the options positional argument.

julia> opts = VideoIO.DEFAULT_CAMERA_OPTIONS
VideoIO.AVDict with 2 entries:
  "framerate"    => "30"
  "pixel_format" => "uyvy422"

julia> opts["framerate"] = "24"
"24"

julia> opts["video_size"] = "640x480"
"640x480"

julia> opencamera(VideoIO.DEFAULT_CAMERA_DEVICE[], VideoIO.DEFAULT_CAMERA_FORMAT[], opts)
VideoReader(...)

Or more simply, change the default. For example:

julia> VideoIO.DEFAULT_CAMERA_OPTIONS["video_size"] = "640x480"

julia> VideoIO.DEFAULT_CAMERA_OPTIONS["framerate"] = 30

julia> julia> opencamera()
VideoReader(...)

Video Properties & Metadata

VideoIO.get_start_time

VideoIO.get_time_duration

VideoIO.get_duration

VideoIO.get_number_frames