How to add external .vtt subtitle file to AVPlayerViewController in tvOS - swift

Question

Question:
How do I add an external WebVTT file to my AVPlayer in tvOS?
Description:
I've been watching this "What's New in HTTP Live Streaming" by Apple where they talk about different ways in implementing an external WebVTT file.
The whole subtitle domain is quite new to me, so I'm having hard time grasping the concept quite well. Within the video they talk about many different things which I do not quite understand such as ( Subtitle playlist ). However, getting passed all that my main concern is adding .vtt file to my AVPlayer.
In the video they talk about this AVMediaSelectionGroup() but I'm quite confused on how to use and how to implement this with my AVPlayerViewController :
class PlayerViewController: AVPlayerViewController {
override func viewDidLoad() {
self.setupVideoPlayerView()
}
private func setupVideoPlayerView()
{
let path = "https://link.to.my.video.mp4"
let subTitlePath = "https://link.to.my.webvtt.file.vtt"
let nsURL = URL(string: path)
let avPlayer = AVPlayer(url: nsURL!)
self.player = avPlayer
self.player!.seek(to: kCMTimeZero)
self.player!.play()
}
}
The AVMediaSelectionGroup doesn't seem to have any methods to add a subtitle? The closest thing I was able to find (that mentioned subtitles) are the following methods:
//Where self is the instance of AVPlayerViewController
self.allowedSubtitleOptionLanguages
self.requiresFullSubtitles

Answer 1

While it was almost mentioned no where in the apple documentation, I read in an article that subtitles need to be embedded in the HLS stream.
Subtitles are not intended to be added manually.. though I did find a StackOverflow post showing a hack. Unsure if it works or not.
Seeing that I use VIMEO Pro, the HLS stream that is provided has the WebVTT subtitles (that I uploaded to vimeo) embedded, thus solving my problem.

Answer 2

This works for me.......
let localVideoAsset = AVURLAsset(url: URL(string: url) ?? URL(string:"")!)
let videoPlusSubtitles = AVMutableComposition()
let videoTrack = videoPlusSubtitles.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
do{
guard localVideoAsset.tracks.count > 0 else{
// error msg
return
}
try? videoTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: localVideoAsset.duration),
of: localVideoAsset.tracks(withMediaType: .video)[0],
at: CMTime.zero)
}
let subtitleURL = URL(fileURLWithPath: model.data?[self.selected].subtitlePath ?? "")
let subtitleAsset = AVURLAsset(url: subtitleURL)
let subtitleTrack = videoPlusSubtitles.addMutableTrack(withMediaType: .text, preferredTrackID: kCMPersistentTrackID_Invalid)
do{
guard subtitleAsset.tracks.count > 0 else{
//error msg
return
}
try? subtitleTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: localVideoAsset.duration),
of: subtitleAsset.tracks(withMediaType: .text)[0],
at: CMTime.zero)
}
let playerViewController = AVPlayerViewController()
let player = AVPlayer(playerItem: AVPlayerItem(asset: videoPlusSubtitles))
playerViewController?.player = player
self.present(playerViewController ?? UIViewController(), animated: true) {
self.videoPlaying = true
self.playerViewController?.player?.play()
}
}

Answer 3

Okay, I think I solve this issue. I was looking for some solutions and I haven't found, so I implemented one to work.
I made available a SPM with the solution and it is quite simple to use. So I called it SimpleSubtitles.
It does support WebVTT, without Styles, and could be improved to support other formats
More info:
https://github.com/peantunes/SimpleSubtitles