Sound and video

The system decodes sound and video (AVFoundation on macOS, Media Foundation on Windows), so the files it plays play: MP3, M4A/AAC, WAV and more for sound; MP4 and MOV (H.264, HEVC) for video. Tessel draws the video’s pictures and controls itself, like its other views.

Playing a sound

playSound(_ path: String, volume: Float = 1.0, loop: Bool = false) -> Sound

Starts playing the file and gives a Sound to control it:

app Jukebox(width: 320, height: 200) {
    state music: Sound? = nil

    HStack {
        Button("Play") { music = playSound(joinPath(appFolder(), "theme.mp3"), loop: true) }
        Button("Pause") { music?.pause() }
        Button("Resume") { music?.resume() }
        Button("Stop") {
            music?.stop()
            music = nil
        }
    }
}

• volume is from 0 (silent) to 1. loop: true plays it over and over.
• A file that can’t be played (it isn’t there, or isn’t sound) gives a Sound that does nothing, and a warning on the terminal.
• A short sound is played and forgotten: playSound(path) on its own.
• Use joinPath(appFolder(), …) for files that come with the app (see appPath and appFolder).

Sound

Method
pause()	Stops where it is.
resume()	Goes on from there (from the start, after its end).
stop()	Stops, and lets the sound go: it can’t be resumed.
seek(to: Float)	Goes to that many seconds in.
setVolume(Float)	From 0 to 1.
isPlaying() -> Bool	Whether it’s playing now.
position() -> Float	Where it is, in seconds.
duration() -> Float	How long it is, in seconds (0 until that’s known).

Showing a video

VideoPlayer(_ path: String, playing: bind Bool = …, position: bind Float = …,
            controls: Bool = true, loop: Bool = false, volume: Float = 1.0)

app Lecture(width: 720, height: 480) {
    state playing = false
    state at = 0.0

    VStack {
        VideoPlayer(joinPath(appFolder(), "lecture.mp4"), playing: playing, position: at)
        Text("{Int(at) / 60} min {Int(at) % 60} s")
    }
    .padding(12)
}

• Controls: a play (pause) button, a bar that shows where it is and is clicked to go there, and its time. They show while it’s paused, and while the pointer is over it. A click elsewhere on the picture plays or pauses. controls: false leaves them out.
• playing:, when it’s bound, plays it (true) or pauses it, and is set back to false when the video comes to its end. Without it, the video starts paused.
• position:, when it’s bound, is where it is in seconds, kept up to date as it plays (a few times a second); setting it jumps there.
• Size: the video’s own, made smaller to fit the space there is (like an Image); a .frame scales it to fit. The picture keeps its shape, on black.

In tests

In a headless run, the players play nothing: each file there is said to be a minute long, and time goes by on the script’s clock (wait 2 moves them two seconds on). tree shows a video’s state:

VideoPlayer "lecture.mp4" playing 2.0/60.0