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• Audio problems when resizing video - moviepy

  17 août 2020, par Jordan

  I am resizing an mp4 video with this code (moviepy) :

  


  video_clip = VideoFileClip(url)
resized = video_clip.resize(width=720)
d = tempfile.mkdtemp()
video_path = os.path.join(d, 'output.mp4')
resized.write_videofile(video_path)


  


  The resized clip's audio works when I play it on my pc, but not on an iPhone. (The original clip's audio does work on my iPhone.)

  


  How can I fix this ?

  


  First image : Codec of resized video
  
Second image : Codec of original video

  


  


  


• How to extract time-accurate video segments with ffmpeg ?

  30 octobre 2023, par Jim Miller

  This is not a particularly new question area around here, but I've tried what's been suggested there without much luck. So, my story :

  


  I've got a hunk of 15 seconds of straight-from-the-camera.mov video out of which I want to extract a specific chunk, which I can identify by start time and stop time, in seconds. I started by trying to do what I'll call a "copy extraction" : to get seconds 9 to 12,

  


  ffmpeg -i test.mov -vcodec copy -acodec copy -ss 9 -to 12 test-copy.mov


  


  This was a not-bad start, but there are some black frames at the beginning and end of the clip, which I can't have — it has to be a clean edit from the original. So, I tried recoding the original into a new, trimmed clip :

  


  ffmpeg -i test.mov -ss 00:00:09 -t 00:00:03 test-out.mov


  


  This is better, but not quite : There are no longer any black frames at the beginning of the clip, but they're still there at the end.

  


  After some more browsing and reading, I then suspected that the problem is that ffmpeg is having trouble finding the proper points because of a lack of keyframes in the original video. So I recoded the original video to (presumably) add keyframes, in a couple of different ways. Since I want to be able to pick video at boundaries of a second ("from 9 seconds to 12 seconds"), I tried, copying various suggestions around the web,

  


  ffmpeg -i test.mov -force_key_frames "expr:gte(t, n_forced)" test-forced.mp4


  


  and

  


  ffmpeg -i test.mov -g 1 test-g-inserted.mp4


  


  (I built these as mp4's based on some comments about an mp4 container being needed to support the keyframe search, but I'm honestly just hacking here.) I then tried the extraction as before, but on these new videos that presumably now have keyframes in them. No luck — both seem to be about the same ; the start is OK but there are still black frames at the end. (FWIW, both test-forced.mp4 and test-g-inserted.mp4 also have trailing black frames.)

  


  So : I'm still stuck, and would like to not be. Any insights out there as to what I'm doing wrong ? I feel like I'm close, but I really need to get rid of those trailing black frames....

  


• Is it possible to "lossless"-ly speed up a video ?

  15 novembre 2020, par Synn Ko

  Might sound like a strange question, but hear me out. I have hours of video I want to cut up and edit together, but a lot of it is just junk I don't need. I don't want to lose any quality, so I use LosslessCut.

  


  The problem for me is that it's... A LOT of footage, and I don't need to see every single second of it. It would be nice if LosslessCut had a button to change the speed of the playback, but it doesn't have that.

  


  So another idea would be to speed up all the videos in advance with ffmpeg, cut them up using LosslessCut, then change the remaining clips back to their original speed using ffmpeg again. Is it possible to speed up a video and change it back to its original speed without losing any quality or changing the video ?