Извлеките значения RGB из AVFrame (FFMPEG) в C++

Если вы видите Cannot subscript a value of type 'String'..., используйте это расширение:

Swift 3

extension String {
    subscript (i: Int) -> Character {
        return self[self.characters.index(self.startIndex, offsetBy: i)]
    }

    subscript (i: Int) -> String {
        return String(self[i] as Character)
    }

    subscript (r: Range) -> String {
        let start = index(startIndex, offsetBy: r.lowerBound)
        let end = index(startIndex, offsetBy: r.upperBound)
        return self[start..) -> String {
        let start = index(startIndex, offsetBy: r.lowerBound)
        let end = index(startIndex, offsetBy: r.upperBound)
        return self[start...end]
    }
}

Swift 2.3

extension String {
    subscript(integerIndex: Int) -> Character {
        let index = advance(startIndex, integerIndex)
        return self[index]
    }

    subscript(integerRange: Range) -> String {
        let start = advance(startIndex, integerRange.startIndex)
        let end = advance(startIndex, integerRange.endIndex)
        let range = start..

Источник: http://oleb.net/blog/2014/07/swift-strings/