How to add transitions between clips in moviepy?

Question

My current attempt:

This is my current code:

from moviepy.editor import *

clips = [VideoFileClip('a.mp4'), VideoFileClip('b.mp4'), VideoFileClip('c.mp4')]
transitioned_clips = [demo_clip.crossfadein(2) for demo_clip in clips]
for_delivery = concatenate_videoclips(transitioned_clips)
for_delivery.write_videofile(target_path, fps=clip.fps, bitrate='%dK' % (bitrate), threads=50, verbose=False, logger=None, preset='ultrafast')

I also tried using CompositeVideoClip, but:

1. It resulted in a completely black video.

2. Even for the completely black video it took 50 times longer to write the video file than for without transitions.

My current output:

My current output is a video with the 3 videos concatenated (which is good), but no transitions between the clips (which is not good).

My goal:

My goal is to add the crossfadein transition for 2 seconds between the clips and concatenate the clips into one video and output it.

In other words, I want it like (in order from left to right):

|        |      +       |        |      +       |        |
| clip 1 | transition 1 | clip 2 | transition 2 | clip 3 |
|        |      +       |        |      +       |        |

---

Is there anyway to have transitions? Any help appreciated.

Answer 1

You could try this approach of manually setting the start time to handle the transitions.

padding = 2

video_clips = [VideoFileClip('a.mp4'), VideoFileClip('b.mp4'), VideoFileClip('c.mp4')]

video_fx_list = [video_clips[0]]

idx = video_clips[0].duration - padding
for video in video_clips[1:]:
    video_fx_list.append(video.set_start(idx).crossfadein(padding))
    idx += video.duration - padding

final_video = CompositeVideoClip(video_fx_list)
final_video.write_videofile(target_path, fps=clip.fps) # add any remaining params

Edit:
Here's an attempt using concatenate:

custom_padding = 2
final_video = concatenate(
    [
        clip1,
        clip2.crossfadein(custom_padding),
        clip3.crossfadein(custom_padding)
    ],
    padding=-custom_padding,
    method="chain"
)
final_video.write_videofile(target_path, fps=clip.fps) # add any remaining params