Frame interpolation using FILM and OpenVINO

This Jupyter notebook can be launched after a local installation only.

Frame interpolation is the process of synthesizing in-between images from a given set of images. The technique is often used for temporal up-sampling to increase the refresh rate of videos or to create slow motion effects. Nowadays, with digital cameras and smartphones, we often take several photos within a few seconds to capture the best picture. Interpolating between these “near-duplicate” photos can lead to engaging videos that reveal scene motion, often delivering an even more pleasing sense of the moment than the original photos.

In “FILM: Frame Interpolation for Large Motion”, published at ECCV 2022, a method to create high quality slow-motion videos from near-duplicate photos is presented. FILM is a new neural network architecture that achieves state-of-the-art results in large motion, while also handling smaller motions well.

The FILM model takes two images as input and outputs a middle image. At inference time, the model is recursively invoked to output in-between images. FILM has three components: 1. Feature extractor that summarizes each input image with deep multi-scale (pyramid) features; 2. Bi-directional motion estimator that computes pixel-wise motion (i.e., flows) at each pyramid level; 3. Fusion module that outputs the final interpolated image.

FILM is trained on regular video frame triplets, with the middle frame serving as the ground-truth for supervision.

In this tutorial, we will use TensorFlow Hub as a model source.

NOTE: To run this tutorial, your system is required to have a VP9 video encoder. Ubuntu has it preinstalled, but for Windows, you should install it manually.

Table of contents:

• Prerequisites

• Prepare images

• Load the model

• Infer the model

  • Single middle frame interpolation

  • Recursive frame generation

• Convert the model to OpenVINO IR

• Inference

  • Select inference device

  • Single middle frame interpolation

  • Recursive frame generation

• Interactive inference

Installation Instructions

This is a self-contained example that relies solely on its own code.

We recommend running the notebook in a virtual environment. You only need a Jupyter server to start. For details, please refer to Installation Guide.

Prerequisites

import os

%pip install -q "tensorflow-macos>=2.5; sys_platform == 'darwin' and platform_machine == 'arm64' and python_version > '3.8'" # macOS M1 and M2
%pip install -q "tensorflow-macos>=2.5,<=2.12.0; sys_platform == 'darwin' and platform_machine == 'arm64' and python_version <= '3.8'" # macOS M1 and M2
%pip install -q "tensorflow>=2.5; sys_platform == 'darwin' and platform_machine != 'arm64' and python_version > '3.8'" # macOS x86
%pip install -q "tensorflow>=2.5,<=2.12.0; sys_platform == 'darwin' and platform_machine != 'arm64' and python_version <= '3.8'" # macOS x86
%pip install -q "tensorflow>=2.5; sys_platform != 'darwin' and python_version > '3.8'"
%pip install -q "tensorflow>=2.5,<=2.12.0; sys_platform != 'darwin' and python_version <= '3.8'"


%pip install -q tensorflow_hub tf_keras numpy "opencv-python" tqdm "gradio>=4.19" Pillow "openvino>=2023.2.0"

%pip install -q "matplotlib>=3.4"

from pathlib import Path
import requests
from typing import Optional, Generator
from datetime import datetime
import gc

os.environ["TF_CPP_MIN_LOG_LEVEL"] = "2"
os.environ["TF_USE_LEGACY_KERAS"] = "1"
os.environ["TFHUB_CACHE_DIR"] = str(Path("./tfhub_modules").resolve())

import tensorflow_hub as hub
import tensorflow as tf
import openvino as ov
import numpy as np
import cv2
import matplotlib.pyplot as plt
from tqdm.auto import tqdm
import gradio as gr
import PIL
import IPython

r = requests.get(
    url="https://raw.githubusercontent.com/openvinotoolkit/openvino_notebooks/latest/utils/notebook_utils.py",
)

open("notebook_utils.py", "w").write(r.text)

from notebook_utils import device_widget

MODEL_PATH = Path("models/model.xml")
DATA_PATH = Path("data")
IMAGES = {
    "https://github.com/openvinotoolkit/openvino_notebooks/assets/29454499/c3ddf65f-95ec-44ca-9ed4-3ef2d8f4b47e": Path("data/one.jpg"),
    "https://github.com/openvinotoolkit/openvino_notebooks/assets/29454499/6d21f1ce-69eb-41b5-aedd-6e3c29013b30": Path("data/two.jpg"),
}
OUTPUT_VIDEO_PATH = DATA_PATH / "output.webm"
OV_OUTPUT_VIDEO_PATH = DATA_PATH / "ov_output.webm"
TIMES_TO_INTERPOLATE = 5
DATA_PATH.mkdir(parents=True, exist_ok=True)

PIL.ImageFile.LOAD_TRUNCATED_IMAGES = True  # allows Gradio to read PNG images with large metadata

Prepare images

Download images and cast them to NumPy arrays to provide as model inputs.

def preprocess_np_frame(frame):
    result = frame.astype(np.float32) / 255  # normalize to [0, 1]
    result = result[np.newaxis, ...]  # add batch dim
    return result


def prepare_input(img_url: str):
    if not IMAGES[img_url].exists():
        r = requests.get(img_url)
        with IMAGES[img_url].open("wb") as f:
            f.write(r.content)
    filename = str(IMAGES[img_url])
    img = cv2.imread(filename)
    img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
    img = np.array(img)
    img = preprocess_np_frame(img)

    return img


input_images = [prepare_input(url) for url in IMAGES]

input = {
    "x0": input_images[0],
    "x1": input_images[1],
    "time": np.array([[0.5]], dtype=np.float32),
}

plt.figure(figsize=(16, 8), layout="tight")
plt.subplot(1, 2, 1)
plt.imshow(input_images[0][0])
plt.axis("off")
plt.subplot(1, 2, 2)
plt.imshow(input_images[1][0])
plt.axis("off");

Load the model

Model is loaded using tensorflow_hub.KerasLayer function. Then, we specify shapes of input tensors to cast loaded object to tf.keras.Model class.

Input tensors are: - time - value between \([0,1]\) that says where the generated image should be. \(0.5\) is midway between the input images. - x0 - initial frame. - x1 - final frame.

For more details, see model page on TensorFlow Hub.

inputs = dict(
    x0=tf.keras.layers.Input(shape=(None, None, 3)),
    x1=tf.keras.layers.Input(shape=(None, None, 3)),
    time=tf.keras.layers.Input(shape=(1)),
)
model_url = "https://www.kaggle.com/models/google/film/frameworks/tensorFlow2/variations/film/versions/1"
film_layer = hub.KerasLayer(model_url)(inputs)
film_model = tf.keras.Model(inputs=inputs, outputs=film_layer)

Infer the model

Single middle frame interpolation

output = film_model(input)
interpolated_image = output["image"][0]
interpolated_image = np.clip(interpolated_image, 0, 1)

def draw(img1, mid_img, img2):
    title2img = {"First frame": img1, "Interpolated frame": mid_img, "Last frame": img2}
    plt.figure(figsize=(16, 8), layout="tight")
    for i, (title, img) in enumerate(title2img.items()):
        ax = plt.subplot(1, 3, i + 1)
        ax.set_title(title)
        plt.imshow(img)
        plt.axis("off")

draw(input_images[0][0], interpolated_image, input_images[1][0])

Recursive frame generation

The process will take as input 2 original frames (first and last) and generate a midpoint frame. Then, it will repeat itself for pairs “first - midpoint”, “midpoint - last” to provide midpoints for them, and so on. Recursion is executed \(t=\) times_to_interpolate times generating \(2^t-1\) images.

class Interpolator:
    def __init__(self, model):
        self._model = model

    def _recursive_generator(
        self,
        frame1: np.ndarray,
        frame2: np.ndarray,
        num_recursions: int,
        bar: Optional[tqdm] = None,
    ) -> Generator[np.ndarray, None, None]:
        """Splits halfway to repeatedly generate more frames.

        Args:
          frame1: Input image 1.
          frame2: Input image 2.
          num_recursions: How many times to interpolate the consecutive image pairs.

        Yields:
          The interpolated frames, including the first frame (frame1), but excluding
          the final frame2.
        """
        if num_recursions == 0:
            yield frame1
        else:
            time = np.array([[0.5]], dtype=np.float32)
            mid_frame = self._model({"x0": frame1, "x1": frame2, "time": time})["image"]
            if bar is not None:
                bar.update(1)
            yield from self._recursive_generator(frame1, mid_frame, num_recursions - 1, bar)
            yield from self._recursive_generator(mid_frame, frame2, num_recursions - 1, bar)

    def interpolate_recursively(self, frame1: np.ndarray, frame2: np.ndarray, times_to_interpolate: int) -> Generator[np.ndarray, None, None]:
        """Generates interpolated frames by repeatedly interpolating the midpoint.

        Args:
          frame1: Input image 1.
          frame2: Input image 2.
          times_to_interpolate: Number of times to do recursive midpoint
            interpolation.

        Yields:
          The interpolated frames (including the inputs).
        """
        num_frames = 2 ** (times_to_interpolate) - 1
        bar = tqdm(total=num_frames)
        yield from self._recursive_generator(frame1, frame2, times_to_interpolate, bar)
        # Separately yield the final frame.
        yield frame2

def save_as_video(frames: Generator[np.ndarray, None, None], width: int, height: int, filename: Path):
    out = cv2.VideoWriter(str(filename), cv2.VideoWriter_fourcc(*"VP90"), 30, (width, height))
    for frame in frames:
        img = frame[0]
        img = np.clip(img, 0, 1)
        rgb_img = img * 255
        rgb_img = rgb_img.astype(np.uint8)
        bgr_img = cv2.cvtColor(rgb_img, cv2.COLOR_RGB2BGR)
        out.write(bgr_img)
    out.release()

height, width = input_images[0][0].shape[:2]
interpolator = Interpolator(film_model)
frames = interpolator.interpolate_recursively(input_images[0], input_images[1], 5)
save_as_video(frames, width, height, OUTPUT_VIDEO_PATH)

OpenCV: FFMPEG: tag 0x30395056/'VP90' is not supported with codec id 167 and format 'webm / WebM'

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IPython.display.Video(filename=OUTPUT_VIDEO_PATH, embed=True)

Convert the model to OpenVINO IR

To convert a TensorFlow Keras Model to OpenVINO Intermediate Representation (IR), call the openvino.convert_model() function and pass the model as the only argument. You can then serialize the model object to disk using the openvino.save_model() function.

if not MODEL_PATH.exists():
    converted_model = ov.convert_model(film_model)
    ov.save_model(converted_model, MODEL_PATH)
    del converted_model
del film_model
gc.collect();

Inference

Select inference device

select device from dropdown list for running inference using OpenVINO

core = ov.Core()
device = device_widget()
device

Dropdown(description='Device:', index=3, options=('CPU', 'GPU.0', 'GPU.1', 'AUTO'), value='AUTO')

compiled_model = core.compile_model(MODEL_PATH, device.value)

Single middle frame interpolation

Model output has multiple tensors, including auxiliary inference data. The main output tensor - interpolated image - is stored at “image” key.

result = compiled_model(input)["image"]
image = result[0]
image = np.clip(image, 0, 1)

Model returned intermediate image. Let’s see what it is.

draw(input_images[0][0], image, input_images[1][0])

Recursive frame generation

Now let’s create a smooth video by recursively generating frames between initial, middle and final images.

height, width = input_images[0][0].shape[:2]
ov_interpolator = Interpolator(compiled_model)
frames = ov_interpolator.interpolate_recursively(input_images[0], input_images[1], TIMES_TO_INTERPOLATE)
save_as_video(frames, width, height, OV_OUTPUT_VIDEO_PATH)

OpenCV: FFMPEG: tag 0x30395056/'VP90' is not supported with codec id 167 and format 'webm / WebM'

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IPython.display.Video(filename=OV_OUTPUT_VIDEO_PATH, embed=True)

Interactive inference

def generate(frame1, frame2, times_to_interpolate, _=gr.Progress(track_tqdm=True)):
    x0, x1 = [preprocess_np_frame(frame) for frame in [frame1, frame2]]
    frames = ov_interpolator.interpolate_recursively(x0, x1, times_to_interpolate)
    height, width = frame1.shape[:2]
    filename = DATA_PATH / f"output_{datetime.now().isoformat()}.webm"
    save_as_video(frames, width, height, filename)
    return filename


if not Path("gradio_helper.py").exists():
    r = requests.get(url="https://raw.githubusercontent.com/openvinotoolkit/openvino_notebooks/latest/notebooks/film-slowmo/gradio_helper.py")
    open("gradio_helper.py", "w").write(r.text)

from gradio_helper import make_demo

demo = make_demo(fn=generate)

try:
    demo.queue().launch(debug=False)
except Exception:
    demo.queue().launch(share=True, debug=False)
# if you are launching remotely, specify server_name and server_port
# demo.launch(server_name='your server name', server_port='server port in int')
# Read more in the docs: https://gradio.app/docs/