Overlay a simple growing/moving progressbar on the bottom of a video using ffmpeg

ffmpeg_overlay_progressbar.py

import subprocess

def add_progressbar_on_top_of_video(
    input_video_filepath: str,
    output_video_filepath: str,
    width: int,
    height: int,
    duration: float,
    fps: float = 25.0,
    progressbar_height: int = 8,
    progressbar_color: str = "#ffffff",
):
    """Overlay a simple filled rect progressbar moving over the screen."""
    px_width_per_frame: float = width / duration / fps

    options = [
        "ffmpeg",
        # First input is our original [video]
        "-i",
        input_video_filepath,
        # Second input exists just to draw on it like on a [canvas]. We
        # need to pass a color here and transparency isn't applicable,
        # so it doesn't really matter, we'll crop it away later anyway.
        "-f",
        "lavfi",
        "-i",
        f"color=black:duration={duration}:rate={fps}:size={width}x{height}",
        # Creation of the progressbar consists of multiple steps:
        "-filter_complex",
        (
            # Assign input node aliases.
            f"""
            [0:v]null[video];
            [1:v]null[canvas];
            """
            # Draw full-width progressbar onto the canvas at the bottom.
            f"""
            [canvas]
                drawbox=
                    w={width}:
                    h={progressbar_height}:
                    x=0:
                    y={height - progressbar_height}:
                    color={progressbar_color}@1.0:
                    thickness=fill
            [progressbar];
            """
            # Crop away the black parts, which moves the progressbar to the top.
            f"""
            [progressbar]
                crop=
                    w={width}:
                    h={progressbar_height}:
                    y={height - progressbar_height}
            [progressbar];
            """
            # Overlay both, moving the progressbar back to the bottom.
            f"""
            [video][progressbar]
                overlay=
                    x=-{width}+(n*{px_width_per_frame}):
                    y={height - progressbar_height}:
                    shortest=1
            [out]
            """
        )
        # Remove the whitespace that helped readability above, but can't
        # be executed.
        .replace(" ", "")
        .replace("\n", ""),
        "-map",
        "[out]",
        # Write results to disk.
        "-y",
        output_video_filepath,
    ]
    subprocess.call(options, stderr=subprocess.STDOUT)


# add_progressbar_on_top_of_video("input_video.mp4", "output_video.mp4", 1920, 1080, duration=5)