ffmpeg-vf-dev

#!/usr/bin/env python3
#
# Play a video and its FFmpeg -vf filtered version side-by-side without creating a video file as intermediary step.
#
# Usage example:
#   ffmpeg-vf-dev video.mp4 "boxblur=10"
#   ffmpeg-vf-dev video.mp4 "boxblur=10" --savePath output.mp4
#
# Docs for writing filters: <https://ffmpeg.org/ffmpeg-filters.html>

import shutil
import subprocess

def main(args):
    if not shutil.which("ffmpeg"):
        print("Could not find `ffmpeg`.")
        return
    if not shutil.which(args.videoPlayer) and not args.savePath:
        print(f"Could not find `{args.videoPlayer}`. You can alternatively use --savePath.")
        return

    ss = f"-ss {args.t0}" if args.t0 else ""
    if not args.savePath or args.saveSideBySide:
        # Side-by-side. Left original, right filtered.
        vf = "-vf \"[0:v]split[half1][half2];[half2]{}[out];[half1][out]hstack\"".format(args.vf)
    else:
        vf = "-vf \"{}\"".format(args.vf)

    if args.savePath:
        out = args.savePath
    else:
        out = f"-f matroska - | {args.videoPlayer} -"
    cmd = f"ffmpeg -i {args.videoPath} {ss} {vf} {out}"
    print(cmd)

    # Display the FFmpeg stderr because it may contain the "File already exists. Overwrite? [y/N]" prompt.
    subprocess.run(cmd, shell=True)

if __name__ == "__main__":
    import argparse
    p = argparse.ArgumentParser(__doc__)
    p.add_argument("videoPath", help="Path to the video to use.")
    p.add_argument("vf", help="FFmpeg `-vf` argument value.")
    p.add_argument("--savePath", help="Save to file instead of playing back live.")
    p.add_argument("--saveSideBySide", action="store_true", help="With --savePath, concatenate the original and filtered videos.")
    p.add_argument("--videoPlayer", default="mpv", help="Installed video player that supports playback from stdin.")
    p.add_argument("--t0", type=float, help="Skip this many seconds from the beginning.")
    args = p.parse_args()
    main(args)