The code below does not show a video output on iOS (works on Android and MacOS) and instead produces errors after asking for camera and mic access.

import QtQuick 2.4
import QtQuick.Window 2.2
import QtQuick.Controls 1.3
import QtMultimedia 5.5

ApplicationWindow {
    width: 640
    height: 360
    visible: true

    Camera {
        id: camera
    }

    VideoOutput {
        source: camera
        width: 100
        height: 100
    }
}

Errors:

QML debugging is enabled. Only use this in a safe environment.
Failed to find shader ":/qtmultimediaquicktools/shaders/rgbvideo_padded.vert"
Failed to find shader ":/qtmultimediaquicktools/shaders/rgbvideo_swizzle.frag"
QOpenGLShader::link: "ERROR: Compiled vertex shader was corrupt.\nERROR: Compiled fragment shader was corrupt.\n"
shader compilation failed:
"ERROR: Compiled vertex shader was corrupt.\nERROR: Compiled fragment shader was corrupt.\n"
QOpenGLShader::link: "ERROR: Compiled vertex shader was corrupt.\nERROR: Compiled fragment shader was corrupt.\n"
QOpenGLShaderProgram::uniformLocation( qt_Matrix ): shader program is not linked
QOpenGLShaderProgram::uniformLocation( width ): shader program is not linked
QOpenGLShaderProgram::uniformLocation( rgbTexture ): shader program is not linked
QOpenGLShaderProgram::uniformLocation( opacity ): shader program is not linked
Failed to find shader ":/qtmultimediaquicktools/shaders/rgbvideo_padded.vert"
Failed to find shader ":/qtmultimediaquicktools/shaders/rgbvideo_swizzle.frag"
QOpenGLShader::link: "ERROR: Compiled vertex shader was corrupt.\nERROR: Compiled fragment shader was corrupt.\n"
shader compilation failed:
"ERROR: Compiled vertex shader was corrupt.\nERROR: Compiled fragment shader was corrupt.\n"
QOpenGLShader::link: "ERROR: Compiled vertex shader was corrupt.\nERROR: Compiled fragment shader was corrupt.\n"