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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).

  


• Multiple overlays using ffmpeg

  23 mars 2018, par lhan

  I’m trying to satisfy a few layering scenarios for building video files using ffmpeg.

  Scenario 1 : Overlay a video (specifying opacity of the video) on top of an image, creating a new video as the result.

  I solved this with :

  ffmpeg -i video.mp4 -i image.jpg -filter_complex '[0]format=rgba,colorchannelmixer=aa=0.7,scale=w=3840:h=2160[a];[1][a]overlay=0:0' -t 30 output.mp4

  I’m scaling the video to 3840x2160 to match my image (ideally I’d have them matching beforehand).

  Scenario 2 : 3 layers now, video - image - image. The middle image layer is a transparent image with text. So we have a base image, with text overlaid, and a video on top of that at a certain opacity.

  I solved this with :

  ffmpeg -i video.mp4 -i image.jpg -i text.png -filter_complex '[0]format=rgba,colorchannelmixer=aa=0.7,scale=w=3840:h=2160[a];[2][a]overlay=0:0,scale=w=3840:h=2160[b];[1][b]overlay=0:0' -t 30 output.mp4

  Scenario 3 (which I can’t get working) : Same as Scenario #2, but with text on top of the video.

  I tried re-arranging my filter, hoping to affect the layering order :

  ffmpeg -i video.mp4 -i image.jpg -i text.png -filter_complex '[2]overlay=0:0,scale=w=3840:h=2160[a];[0][a]format=rgba,colorchannelmixer=aa=0.7,scale=w=3840:h=2160[b];[1][b]overlay=0:0' -t 5 output.mp4

  But that gives the following error :

  Too many inputs specified for the "format" filter. Error initializing complex filters. Invalid argument

  Full Error :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from ’video.mp4’ :
  Metadata :
  major_brand : mp42
  minor_version : 0
  compatible_brands : mp42mp41
  creation_time : 2018-03-09T20:52:18.000000Z

  Duration : 00:00:30.00, start : 0.000000, bitrate : 8002 kb/s

  Stream #0:0(eng) : Video : h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 7997 kb/s, 24 fps,
  24 tbr, 24k tbn, 48 tbc (default)

  Metadata :
  creation_time : 2018-03-09T20:52:18.000000Z
  handler_name : Alias Data Handler
  encoder : AVC Coding Input #1, image2, from ’image.jpg’ :

  Duration : 00:00:00.04, start : 0.000000, bitrate : 526829 kb/s

  Stream #1:0 : Video : mjpeg, yuvj444p(pc, bt470bg/unknown/unknown), 3840x2160 [SAR 96:96 DAR 16:9], 25 tbr, 25 tbn, 25 tbc Input #2,
  png_pipe, from ’text.png’ : Duration : N/A, bitrate : N/A

  Stream #2:0 : Video : png, rgba(pc), 1500x1500, 25 tbr, 25 tbn, 25 tbc [AVFilterGraph @ 0x7fc37d402de0]

  Too many inputs specified for the "format" filter. Error initializing complex filters. Invalid argument

  I can sort of get around that by tweaking the command so that the text isn’t an input to the overlay :

  ffmpeg -i lightTexture.mp4 -i image.jpg -i textSample.png -filter_complex '[2]overlay=0:0,scale=w=3840:h=2160;[0]format=rgba,colorchannelmixer=aa=0.7,scale=w=3840:h=2160[b];[1][b]overlay=0:0' -t 5 output_text_on_top.mp4

  But then my output video is all messed up. I suspect I am on the wrong track by trying to cram all of this into the -filter_complex. I’m wondering if I need to create two overlays and then overlay those (i.e overlay Text onto the Video, and then overlay that onto the base image) though I’m not sure how to accomplish that.

  If anyone could point me in the right direction here, I’d be super grateful.

• Fix a .WAV header

  28 décembre 2018, par Mattia Mura

  A Ransomware crypted all my files a little time ago, I started studying a way to come over that and I discovered that the ransomware only changes the code of each files up until Offset no.100000. This helped me recovering many of my files just copying and pasting those code lines on the corrupted files from other files with a similiar .ext that werent’t damaged. It has been easy with huge video files and also with some audio files like .3gp or .mp3, but I’m having big issues with a .wav file of 152 MB containing some important audio from an interview.

  I am using HxD to manipulate the code and ffmpeg to fix some of the parts of my files after this copy/paste process. I’ve already tried to fix everything with vlc but it gave me no results

  HERE is the beginning of the file, that doesn’t have any ordinary .wav header anymore because of the encryption.

  And HERE you can see the difference between offset FFFF0 and 100000, to give you a clearer idea.

  Basically I should change the code of the file up until the Offset number 100000, or anyway I should make it work despite those crypted lines. Do you know any way to solve this issue ? Thanks a lot and be patient, is my first question here !