Movie Texture Blending

Thanks for the solution. Nevertheless the two movies do not always run perfectly synchronized. So I tried to have one movie only that includes both: it is double height, has the normal video on top and the grayscale video for the mask on bottom. The material uses this one movie for both textures, while the tilings and offsets are adapted. But for the culling mask the tiling and offset values are ignored - it looks like I need to adapt the shader, but sadly I have no idea about shader scripting. Any help?

I made this shader in shaderforge works pretty well

 // Shader created with Shader Forge v1.21 
 // Shader Forge (c) Neat Corporation / Joachim Holmer - http://www.acegikmo.com/shaderforge/
 // Note: Manually altering this data may prevent you from opening it in Shader Forge

 Shader "0_CD/VideoMaskedColored" {
     Properties {
         _MainTex ("MainTex", 2D) = "white" {}
         _Mask ("Mask", 2D) = "white" {}
         _Transparency ("Transparency", Range(0, 1)) = 0
         _Color ("Color", Color) = (0.4485294,0.310013,0.310013,1)
         [HideInInspector]_Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
     }
     SubShader {
         Tags {
             "IgnoreProjector"="True"
             "Queue"="Transparent"
             "RenderType"="Transparent"
         }
         Pass {
             Name "FORWARD"
             Tags {
                 "LightMode"="ForwardBase"
             }
             Blend SrcAlpha OneMinusSrcAlpha
             ZWrite Off
             
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #define UNITY_PASS_FORWARDBASE
             #include "UnityCG.cginc"
             #include "UnityPBSLighting.cginc"
             #include "UnityStandardBRDF.cginc"
             #pragma multi_compile_fwdbase
             #pragma exclude_renderers gles3 metal d3d11_9x xbox360 xboxone ps3 ps4 psp2 
             #pragma target 3.0
             uniform sampler2D _MainTex; uniform float4 _MainTex_ST;
             uniform sampler2D _Mask; uniform float4 _Mask_ST;
             uniform float _Transparency;
             uniform float4 _Color;
             struct VertexInput {
                 float4 vertex : POSITION;
                 float2 texcoord0 : TEXCOORD0;
             };
             struct VertexOutput {
                 float4 pos : SV_POSITION;
                 float2 uv0 : TEXCOORD0;
             };
             VertexOutput vert (VertexInput v) {
                 VertexOutput o = (VertexOutput)0;
                 o.uv0 = v.texcoord0;
                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex );
                 return o;
             }
             float4 frag(VertexOutput i) : COLOR {
 /////// Vectors:
 ////// Lighting:
 ////// Emissive:
                 float4 _MainTex_var = tex2D(_MainTex,TRANSFORM_TEX(i.uv0, _MainTex));
                 float3 emissive = (_Color.rgb*_MainTex_var.rgb);
                 float3 finalColor = emissive;
                 float4 _Mask_var = tex2D(_Mask,TRANSFORM_TEX(i.uv0, _Mask));
                 return fixed4(finalColor,((lerp( lerp( lerp( _Mask_var.b, _Mask_var.r, _Mask_var.rgb.r ), _Mask_var.g, _Mask_var.rgb.g ), _Mask_var.b, _Mask_var.rgb.b ))*_Transparency));
             }
             ENDCG
         }
     }
     FallBack "Diffuse"
     CustomEditor "ShaderForgeMaterialInspector"
 }
 

"it does'nt work with CSharp. Do it in Javascript it will work ;)"

You can do it in C#. For playing the movie texture and the movie mask just drop this script onto the same object that uses the shader above:

 public class MovieTextureWithAlphaMask: MonoBehaviour {

   private MovieTexture mask;
   private MovieTexture mainTex;

void Start () { mask = (MovieTexture)renderer.material.GetTexture("_Mask"); mainTex = (MovieTexture)renderer.material.GetTexture("_MainTex"); }

void Update () { if (Input.GetButtonDown("Jump")) { mainTex.Play(); mask.Play(); } } }

One thing I noticed, however, is that there seems to be a tiny delay between the movie and the mask so they may not line up perfectly when they are played.