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• Cut a video in between key frames without re-encoding the full video using ffpmeg ? [closed]

  13 juillet 2024, par bguiz

  I would like to cut a video at the beginning at any particular timestamp, and it need to be precise, so the nearest key frame is not good enough.

  


  Also, these videos are rather long - an hour or longer - so I would like to avoid re-encoding this altogether if possible, or otherwise only re-encode a minimal fraction of the total duration. Thus, would like to maximise the use of -vcodec copy.

  


  How can I accomplish this using ffmpeg ?

  


  NOTE : See scenario, and my own rough idea for a possible solution below.

  


  ---

  


  Scenario :

  


  

  • Original video

    

    • Length of 1:00:00

    


    • Has a key frame every 10s

    


    


  


  • Desired cut :

    

    • From 0:01:35 through till the end

    


    


  


  • Attempt #1 :

    

    • Using -ss 0:01:35 -i blah.mp4 -vcodec copy, what results is a file where :

    


    • audio starts at 0:01:30

    


    • video also starts at 0:01:30

    


    • this starts both the audio and the video too early

    


    


  


  • using -i blah.mp4 -ss 0:01:35 -vcodec copy, what results is a file where :

    

    • audio starts at 0:01:35,

    


    • but the video is blank/ black for the first 5 seconds,

      

      • until 0:01:40, when the video starts

      


      


    


    • this starts the audio on time,
but the video starts too late

    


    


  


  


  ---

  


  Rough idea

  


  

  • (1) cut 0:01:30 to 0:01:40

    

    • re-encode this to have new key frames,
including one at the target time of 0:01:35

    


    • then cut this to get the 5 seconds from 0:01:35 through 0:01:40

    


    


  


  • (2) cut 0:01:40 through till the end

    

    • without re-encoding, using -vcodec copy

    


    


  


  • (3) ffmpeg concat the first short clip (the 5 second one)
with the second long clip

  


  


  I know/ can work out the commands for (2) and (3), but am unsure about what commands are needed for (1).

  


• Auto resize video with ffmpeg based on input video resolution

  12 mai 2018, par Masoud Mohammadi

  I wrote a Bash script to convert all video files in a directory. Some videos are 1280 x 720 resolution, and others are 720 x 1280.

  How can I write a ffmpeg command that converts 1280 x 720 videos to 640 x 360 and 720 x 1280 videos to 360 x 640 ?

• How to speed up processing for FFmpeg video overlay on a video source file in Android ?

  28 décembre 2017, par Iffat Fatima

  I am working on an Android application to add a video file as an overlay on another video file, along with adding an audio stream to it, using FFmpeg library for Android.

  I am using the following command to apply the overlay, but for a video of 2 seconds, it takes 55 seconds to process. Is there a way to speed up this process ?

      String[] complexCmd = new String[]{ "-y",    
  
              "-i",               
  
              originalVideoPath,        
  
              "-i",               
  
              overlayVideoPath ,       
  
              "-i",               
  
              audioPath,              
  
              "-filter_complex",  
  
              "[0:v]setpts=PTS-STARTPTS[top];[1:v]setpts=PTS-STARTPTS, scale="+newOverlayWidth+"x"+newOverlayHeight+",format=yuva420p,colorchannelmixer=aa=0.5[bottom];[top][bottom]overlay=shortest=1:x="+left+":y="+top+"" ,
  
              "-c:v",
  
              "libx264",
  
              "-preset",
  
              "ultrafast",
  
              "-crf",
  
              "28",  
  
              "-map",  
  
              "2:a",  
  
              "-shortest",
  
              destVideoPath,
  
      };