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• 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....

  


• Widescreen Converter for mp4 Video files [duplicate]

  25 février 2017, par seking

  This question already has an answer here :

  • FFmpeg : How to convert vertical video with black sides, to video 16:9, with blurred background sides
    
    2 answers
    

  i am looking for a possibility ( php / linux ) to convert any kind of mp4 video into a widescreen format... like a picture widescreen converter

  

  The left and right part of the image does not need to be blurred.. it could be black as well. I don’t care.

  The program should recognize if the video is not 16:9 format and then convert it.

  Is this possible with ffmpeg ? I cannot find a solution for this but I have seen converted videos like that.

  EDIT : Found the solution !

• Anomalie #2748 (Nouveau) : Dénoncées les erreurs dans les boucles DATA pour yql

  6 juin 2012, par cam.lafit -

  Ciao Lorsqu’on effecture une boucle yql et que celle ci est mal formée, le compilateur dénonce seulement "réponse vide ou mal formée" alors qu’il est possible d’être plus explicite. Exemple avec ce cas testé Si on essaye la boucle select * from flickr.photos.search(10) where user_id=’unidflickr’ (...)