run with -> $ uv run https://gist.githubusercontent.com/kolibril13/d9f24596620a1a0ec278841ae3e7653c/raw/af321732a1a2a3b0b859c5324262dd7f680f6a8a/concat_two_videos_fade.py

concat_two_videos_fade.py

#!/usr/bin/env python3
# /// script
# requires-python = ">=3.11"
# dependencies = [
#     "ffmpeg-python",
# ]
# ///
"""
This script takes two MP4 videos and creates a transition where:
 - Video1 is extended by 0.5 seconds (via a frozen last frame) and the final 0.2 seconds
   of that extension fade out to gray.
 - Video2 is prepended with a 0.5-second freeze of its first frame, where the first 0.2
   seconds fade in from gray.
If video2’s resolution differs from video1’s, video2 is scaled and padded accordingly.
"""

from pathlib import Path
import ffmpeg

def get_video_info(file_path: Path):
    """Probe the video to get width, height, and duration."""
    probe = ffmpeg.probe(str(file_path))
    video_stream = next((s for s in probe['streams'] if s['codec_type'] == 'video'), None)
    if video_stream is None:
        raise ValueError(f"No video stream found in {file_path}")
    width = int(video_stream['width'])
    height = int(video_stream['height'])
    duration = float(probe['format']['duration'])
    return width, height, duration

def main():
    folder_path = Path.home() / "Desktop"
    video1_path = folder_path / "video1.mp4"
    video2_path = folder_path / "video2.mp4"

    # Get video info
    v1_width, v1_height, v1_duration = get_video_info(video1_path)
    v2_width, v2_height, v2_duration = get_video_info(video2_path)

    # Parameters for the extension and fades:
    ext_duration = 0.8         # How much to extend each video (in seconds)
    fade_out_duration = 0.2    # Fade-out length on video1's freeze extension
    fade_in_duration = 0.2     # Fade-in length on video2's freeze extension
    # For video1's freeze extension, the fade should start at 0.5 - 0.2 = 0.3 seconds
    fade_out_start = ext_duration - fade_out_duration

    # Load inputs
    v1 = ffmpeg.input(str(video1_path))
    v2 = ffmpeg.input(str(video2_path))

    # --- Process Video1 ---
    # 1. Original video1 remains untouched.
    v1_orig = (
        v1.video
        .filter('trim', start=0, end=v1_duration)
        .filter('setpts', 'PTS-STARTPTS')
    )

    # 2. Create a freeze extension of ext_duration seconds at the end.
    #    Use tpad to append a frozen frame, then extract the appended portion.
    v1_extended = v1.video.filter('tpad', stop_mode='clone', stop_duration=ext_duration)
    v1_freeze = (
        v1_extended
        .filter('trim', start=v1_duration, end=v1_duration + ext_duration)
        .filter('setpts', 'PTS-STARTPTS')
    )
    # 3. Apply fade-out (to gray) on the last 0.2 seconds of the freeze extension.
    v1_freeze_fade = v1_freeze.filter(
        'fade',
        type='out',
        start_time=fade_out_start,
        duration=fade_out_duration,
        color='gray'
    )

    # 4. Concatenate the original part and the freeze extension with fade.
    v1_final = ffmpeg.concat(v1_orig, v1_freeze_fade, v=1, a=0)

    # --- Process Video2 ---
    # For video2, if needed, scale and pad to match video1's resolution.
    if v2_width != v1_width or v2_height != v1_height:
        scale_factor = min(v1_width / v2_width, v1_height / v2_height)
        new_width = int(v2_width * scale_factor)
        new_height = int(v2_height * scale_factor)
        v2_video = (
            v2.video
            .filter('scale', width=new_width, height=new_height)
            .filter('pad',
                    w=v1_width,
                    h=v1_height,
                    x=f'({v1_width}-iw)/2',
                    y=f'({v1_height}-ih)/2',
                    color='black')
        )
    else:
        v2_video = v2.video

    # Prepend video2 with a ext_duration second freeze (using tpad with start_mode=clone).
    v2_extended = v2_video.filter('tpad', start_mode='clone', start_duration=ext_duration)
    # Apply a fade-in (from gray) on the first 0.2 seconds.
    v2_final = (
        v2_extended
        .filter('fade', type='in', start_time=0, duration=fade_in_duration, color='gray')
        .filter('setpts', 'PTS-STARTPTS')
    )

    # --- Concatenate Video1 and Video2 ---
    transitioned_video = ffmpeg.concat(v1_final, v2_final, v=1, a=0)

    # Output the final video
    output_path = folder_path / "output_with_transition.mp4"
    out = ffmpeg.output(
        transitioned_video,
        str(output_path),
        vcodec='libx264',
        movflags='+faststart'
    )
    out.run(overwrite_output=True)
    print(f"Transition video created: {output_path}")

if __name__ == '__main__':
    main()