[Bug] AVAsset tracks is sometimes empty

[KasemJaffer]

Description

asset.tracks(withMediaType: AVMediaType.video).first! is sometimes crashing the app. Simply initializing the AVAsset is not enough for the asset to be ready to access its tracks.

Platform

IOS

Expected solution

AVAsset needs to be loaded first before accessing any of its tracks.

Here is an example of how to fix it.

    public func getTrack(_ asset: AVURLAsset)->AVAssetTrack? {
        var track : AVAssetTrack? = nil
        let group = DispatchGroup()
        group.enter()
        asset.loadValuesAsynchronously(forKeys: ["tracks"], completionHandler: {
            var error: NSError? = nil;
            let status = asset.statusOfValue(forKey: "tracks", error: &error)
            if (status == .loaded) {
                track = asset.tracks(withMediaType: AVMediaType.video).first
            }
            group.leave()
        })
        group.wait()
        return track
    }