Transitions (View/Rescaler)

This guide will show a few basic examples of animated transitions on View/Rescaler components.

Configure inputs and output

Start the compositor and configure 2 input streams and a single output stream as described in the "Simple scene" guide in the "Configure inputs and output" section.

Transition that changes the width of an input stream

HTTP

Set initial scene for the transition:

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 480,
          "child": { "type": "input_stream", "input_id": "input_1" },
        }
      ]
    }
  }
}

A few seconds latter update a scene with a different width:

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 1280,
          "transition": { "duration_ms": 2000 },
          "child": { "type": "input_stream", "input_id": "input_1" },
        }
      ]
    }
  }
}

Membrane Framework

Set initial scene for the transition and after few seconds update a component with a different width:

def handle_setup(ctx, state) do
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 480,
          child: %{ type: :input_stream, input_id: :input_1 },
        }
      ]
    }
  }
  Process.send_after(self(), :start_transition, 2000)
  {[notify_child: {:live_compositor, request}], state}
end

def handle_info(:start_transition, _ctx, state)
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 1280,
          transition: %{ duration_ms: 2000 },
          child: %{ type: :input_stream, input_id: :input_1 },
        }
      ]
    }
  }
  {[notify_child: {:live_compositor, request}], state}
end

In the first update request, you can see that the rescaler has a width of 480, and in the second one, it is changed to 1280 and transition.duration_ms: 2000 was added.

The component must have the same "id" in both the initial state and the update that starts the transition, otherwise it will switch immediately to the new state without a transition.

Output stream

Transition on one of the sibling components

In the above scenario you saw how transition on a single component behaves, but let's see what happens with components that are not a part of the transition, but their size and position still depend on other components.

Add a second input stream wrapped with Rescaler, but without any transition options.

HTTP

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 480,
          "child": { "type": "input_stream", "input_id": "input_1" },
        },
        {
          "type": "rescaler",
          "child": { "type": "input_stream", "input_id": "input_2" },
        }
      ]
    }
  }
}

Update a scene with a different width:

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 1280,
          "transition": { "duration_ms": 2000 },
          "child": { "type": "input_stream", "input_id": "input_1" },
        },
        {
          "type": "rescaler",
          "child": { "type": "input_stream", "input_id": "input_2" },
        }
      ]
    }
  }
}

Membrane Framework

def handle_setup(ctx, state) do
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 480,
          child: %{ type: :input_stream, input_id: :input_1 },
        },
        %{
          type: :rescaler,
          child: %{ type: :input_stream, input_id: :input_2 },
        }
      ]
    }
  }
  Process.send_after(self(), :start_transition, 2000)
  {[notify_child: {:live_compositor, request}], state}
end

def handle_info(:start_transition, _ctx, state)
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 1280,
          transition: %{ duration_ms: 2000 },
          child: %{ type: :input_stream, input_id: :input_1 },
        },
        %{
          type: :rescaler,
          child: %{ type: :input_stream, input_id: :input_2 },
        }
      ]
    }
  }
  {[notify_child: {:live_compositor, request}], state}
end

Output stream

Transition between different modes

Currently, a state before the transition and after needs to use the same type of configuration. In particular:

• It is not possible to transition a component between static and absolute positioning.
• It is not possible to transition a component between using top and bottom fields (the same for left/right).
• It is not possible to transition a component with known width/height to a state with dynamic width/height based on the parent layout.

Let's try the same example as in the first scenario with a single input, but instead, change the Rescaler component to be absolutely positioned in the second update.

HTTP

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 480,
          "child": { "type": "input_stream", "input_id": "input_1" },
        }
      ]
    }
  }
}

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 1280,
          "top": 0,
          "left": 0,
          "transition": { "duration_ms": 2000 },
          "child": { "type": "input_stream", "input_id": "input_1" },
        }
      ]
    }
  }
}

Membrane Framework

def handle_setup(ctx, state) do
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 480,
          child: %{ type: :input_stream, input_id: :input_1 },
        }
      ]
    }
  }
  Process.send_after(self(), :start_transition, 2000)
  {[notify_child: {:live_compositor, request}], state}
end

def handle_info(:start_transition, _ctx, state)
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 1280,
          top: 0,
          left: 0,
          transition: %{ duration_ms: 2000 },
          child: %{ type: :input_stream, input_id: :input_1 },
        }
      ]
    }
  }
  {[notify_child: {:live_compositor, request}], state}
end

As you can see on the resulting stream, the transition did not happen because the Rescaler component in the initial scene was using static positioning and after the update it was positioned absolutely.

Output stream

Different interpolation functions

All of the above examples use default linear interpolation, but there are also a few other modes available.

HTTP

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 320, "height": 180, "top": 0, "left": 0,
          "child": { "type": "input_stream", "input_id": "input_1" },
        },
        {
          "type": "rescaler",
          "id": "rescaler_2",
          "width": 320, "height": 180, "top": 0, "left": 320,
          "child": { "type": "input_stream", "input_id": "input_2" },
        },
        {
          "type": "rescaler",
          "id": "rescaler_3",
          "width": 320, "height": 180, "top": 0, "left": 640,
          "child": { "type": "input_stream", "input_id": "input_3" },
        },
        {
          "type": "rescaler",
          "id": "rescaler_4",
          "width": 320, "height": 180, "top": 0, "left": 960,
          "child": { "type": "input_stream", "input_id": "input_4" },
        },
      ]
    }
  }
}

POST: /api/output/output_1/update
Content-Type: application/json

{
  "video": {
    "root": {
      "type": "view",
      "background_color_rgba": "#4d4d4dff",
      "children": [
        {
          "type": "rescaler",
          "id": "rescaler_1",
          "width": 320, "height": 180, "top": 540, "left": 0,
          "child": { "type": "input_stream", "input_id": "input_1" },
          "transition": { "duration_ms": 2000 },
        },
        {
          "type": "rescaler",
          "id": "rescaler_2",
          "width": 320, "height": 180, "top": 540, "left": 320,
          "child": { "type": "input_stream", "input_id": "input_2" },
          "transition": {
            "duration_ms": 2000, "easing_function": {"function_name": "bounce"}
          },
        },
        {
          "type": "rescaler",
          "id": "rescaler_3",
          "width": 320, "height": 180, "top": 540, "left": 640,
          "child": { "type": "input_stream", "input_id": "input_3" },
          "transition": {
            "duration_ms": 2000,
            "easing_function": {
                "function_name": "cubic_bezier",
                "points": [0.65, 0, 0.35, 1]
            }
          }
        },
        {
          "type": "rescaler",
          "id": "rescaler_4",
          "width": 320, "height": 180, "top": 540, "left": 960,
          "child": { "type": "input_stream", "input_id": "input_4" },
          "transition": {
            "duration_ms": 2000,
            "easing_function": {
              "function_name": "cubic_bezier",
              "points": [0.33, 1, 0.68, 1]
            }
          }
        }
      ]
    }
  }
}

Membrane Framework

def handle_setup(ctx, state) do
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 320, height: 180, top: 0, left: 0,
          child: %{ type: :input_stream, input_id: :input_1 },
        },
        %{
          type: :rescaler,
          id: "rescaler_2",
          width: 320, height: 180, top: 0, left: 320,
          child: %{ type: :input_stream, input_id: :input_2 },
        },
        %{
          type: :rescaler,
          id: "rescaler_3",
          width: 320, height: 180, top: 0, left: 640,
          child: %{ type: :input_stream, input_id: :input_3 },
        },
        %{
          type: :rescaler,
          id: "rescaler_4",
          width: 320, height: 180, top: 0, left: 960,
          child: %{ type: :input_stream, input_id: :input_4 },
        }
      ]
    }
  }
  Process.send_after(self(), :start_transition, 2000)
  {[notify_child: {:live_compositor, request}], state}
end

def handle_info(:start_transition, _ctx, state)
  request = %LiveCompositor.Request.UpdateVideoOutput{
    output_id: "output_1",
    root: %{
      type: :view,
      background_color_rgba: "#4d4d4dff",
      children: [
        %{
          type: :rescaler,
          id: "rescaler_1",
          width: 320, height: 180, top: 0, left: 0,
          child: %{ type: :input_stream, input_id: :input_1 },
          transition: %{ duration_ms: 2000 },
        },
        %{
          type: :rescaler,
          id: "rescaler_2",
          width: 320, height: 180, top: 0, left: 320,
          child: %{ type: :input_stream, input_id: :input_2 },
          transition: %{
            duration_ms: 2000
            easing_function: %{ function_name: :bounce}
          },
        },
        %{
          type: :rescaler,
          id: "rescaler_3",
          width: 320, height: 180, top: 0, left: 640,
          child: %{ type: :input_stream, input_id: :input_3 },
          transition: %{
            duration_ms: 2000
            easing_function: %{
              function_name: :cubic_bezier,
              points: [0.65, 0, 0.35, 1]
            }
          }
        },
        %{
          type: :rescaler,
          id: "rescaler_4",
          width: 320, height: 180, top: 0, left: 960,
          child: %{ type: :input_stream, input_id: :input_4 },
          transition: %{
            duration_ms: 2000
            easing_function: %{
              function_name: :cubic_bezier,
              points: [0.33, 1, 0.68, 1]
            }
          }
        }
      ]
    }
  }
  {[notify_child: {:live_compositor, request}], state}
end

Output stream

• Input 1 - Linear transition
• Input 2 - Bounce transition
• Input 3 - Cubic Bézier transition with [0.65, 0, 0.35, 1] points (easeInOutCubic)
• Input 4 - Cubic Bézier transition with [0.33, 1, 0.68, 1] points (easeOutCubic)

Check out other popular Cubic Bézier curves on https://easings.net.