MoviePy smaller clip splitting causing glitches when concatenating files, mismatched audio, encoding

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My code is below. The breaker file:

from moviepy.video.io.ffmpeg_tools import ffmpeg_extract_subclip

splits = [[1, 2], [5, 6], [7, 10]]

for i, split in enumerate(splits):
  start, end = split
  ffmpeg_extract_subclip("video.m4v", start, end, targetname="clips/{0}.mp4".format(i))

This breaker code works and successfully breaks the clips into their proper lengths. When opening them, I get errors such as:

  1. Glitchy tearing when opening the sub-clips in VLC (example)
  2. Incorrect length of video in comparison to its actual length being watched
  3. In Vegas for example, the audio is shorter than the video for each sub-clip
  4. When trying to concatenate these videos into one larger video (code below), when the clips are joined the "transition" repeats the last few moments of the previous video for a few seconds before playing the new clip

Code for the concatenation:

from moviepy.editor import *

clips = []
for i in range(1, 3):
  clips.append(VideoFileClip("{0}.mp4".format(i)))

concat = concatenate_videoclips(clips)
concat.write_videofile("output.mp4")

This works also, though upon opening I get the error written in point (4) above.

Extra information:

  • I've used two original versions of the same video, one is the original video (2.42gb) and the other is a version I ran through Handbrake's encoding to make sure that wasn't the issue.
  • I've encoded the output as well incase that was the issue (Handbrake again) and the issue stayed the same.
  • This was not an issue yesterday when running both bits of code, and the only actions I've done since then were attempt to reinstall MoviePy (pip uninstall moviepy -> pip install moviepy==1.0.1, I'm currently on version 1.0.3 -- if there's something I'm missing from a default install of Python, please let me know)
  • The issue is not syntax-error related, I've paraphrased code to make it easier to read

Here is a screenshot of Vegas viewing these files individually (I have not cut them, this is just me pasting them directly into Vegas):

image of sony vegas with this moviepy issue

Update: I've tried downloading the exe of FFMPEG and calling it directly for my splitting (not using the Python-downloaded version // moviepy link to FFMPEG) and the issue is still persisting. I got the idea from this Stack post.

Update: I've tried many things to rule-out the original file being split as the issue, but I am beginning to believe that the issue is heavily emphasized on the concatenation file. Will try to work at finding older versions of this function.

Update: for every version I change of MoviePy, something offputting changes. In 2.0.0, the end of the sub-clip is frozen whilst no audio plays. In 1.0.0 the start of the clip glitches. In 1.0.1-2, the end of the clip glitches as it moves into the new one. Extremely confused.

Update: I just can't track down what angle to attack this issue at. For example: I try a different video and on the first run its semi-workable (throw into Vegas, move it around to get the right times, render it as a passable video) but as soon as I make a change (like trying to add a second or two to when it clips) its as if everything just desyncs and gives up. Once I return to the normal clipping before (that was workable) the clipping is not predictable at all, and is in a total desync. All I'm looking for right now is something to uninstall and reinstall, or an alternative.

moviepy video python
1 Answers

The Glitch is because You probably do not have a keyframe at the specified timestamp. Because non-keyframes encode differences from nearest keyframes, they show only the differences from previous keyframe, thats why they are very memory effecient, but not consistent . similar theory goes for audio too and depends on codec/format ofc!

at core moviePY also use ffmpeg tool, here is the official page for API reference, and under the hood details, https://zulko.github.io/moviepy/_modules/moviepy/video/io/ffmpeg_tools.html

With the mp4 container it is possible to cut at a non-keyframe without re-encoding using an edit list (Problem about edit list). In other words, if the closest keyframe before 3s is at 0s then it will copy the video starting at 0s and use an edit list to tell the player to start playing not at 3 seconds but at 0s since its the nearest keyframe rest frames are dropped. that is the reason why sometimes the audio plays and video image hangs, but timeline keeps running.

what you did , IT DOES NOT RE-ENCODE THE ORIGNAL STUFF! it just splits at nearest keyframes to your specified start/end times and they are not equally spaced, hence the unequal lengths of final result.

Dont do this: Even though It is the fastest and best ffmpeg-way I have figure it out,and that's what i assume your method is doing:

ffmpeg -ss 00:01:00 -i input.mp4 -to 00:02:00 -c copy output.mp4

but the below thing will cut and re encode:

ffmpeg -i movie.mp4 -ss 00:00:03 -t 00:00:08 -async 1 cut.mp4

When re-encoding you may also wish to include additional codec options then use this::

ffmpeg -ss 00:03:00 -t 00:00:05 -i test.wmv -acodec libmp3lame -vcodec libx264 1.mp4

But swami Whats the difference?

We are not using the -c copy parameter. hence not just dumping the raw I/O stream. but re encoding it again, more cpu work required!

Also, the -t option specifies a duration, not an end time. The above command (second code snippet) will encode 8s of video starting at 3s. To start at 3s and end at 8s use -t 5 (3rd code snippet).

NOTES: If you are using a current version of ffmpeg (above 2015 i guess) you can also replace -t with -to in the above command to end at the specified time.

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