Movies

mdapy.visualization.write_movie writes pictures as a movie with FFmpeg, which must be on the PATH: conda install ffmpeg, brew install ffmpeg or apt install ffmpeg. MDAPY does not ship it.

from mdapy.io import read_trajectory
from mdapy.visualization import render, write_movie

frames = read_trajectory("run.dump")
camera = dict(view="iso", focus=(50.0, 50.0, 50.0), span=150.0)
pictures = (
    render(frame, width=1280, height=720, device="auto", **camera) for frame in frames
)
write_movie("run.mp4", pictures, fps=30)

Give the pictures as a generator, as here: each is drawn when the movie needs it, so a long movie is not held in memory. Fix the frame with focus and span, or each picture frames its own atoms and the movie jumps.

Parameters

write_movie(path, pictures, *, fps=30)

Name	Type	Default	Unit	Meaning
path	str or path-like			the file; its suffix, such as .mp4, tells FFmpeg the format
pictures	iterable of (H, W, 3) or (H, W, 4) uint8			(H, W, 3) or (H, W, 4) uint8 images of one size, as render gives them
fps	float64	30	1/s	pictures per second

The movie is H.264 where FFmpeg offers it, the usual choice for .mp4, with a picture of odd size padded to even sizes for players. Draw the pictures with a background: a movie has no transparency.

Errors

write_movie raises:

• FileNotFoundError when FFmpeg is not on the PATH;
• InvalidParameter when fps is not positive, there are no pictures, a picture is not an image of the size of the first, or they hold more than 8192 × 4320 pixels, the largest size of H.264;
• CalculationFailed when FFmpeg fails, with what it says.

The tutorial A movie that flies through a crystal makes a movie from one system.