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• Cut a video in between key frames without re-encoding the full video using ffpeg ?

  1er septembre 2020, 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).

  


• How to measure delay in video streaming (RTMP) from NGinX server to video player in web browser ?

  2 mars 2020, par Padfoot

  I am streaming a MP4 file from AWS NGinX server (using FFMPEG) to a video player (currently using flowplayer in web page).
  I am trying to identify how long the player will take to get the first packet of frames from the server. Is there any utility or method to measure.

  I have already checked few previous questions in stackoverflow, and found out about webrtc chrome://webrtc-internals/.

• How to overlay a video on another video and also fade in a PNG

  3 février 2019, par Imonaboat

  I am looking to overlay a video on top of another video and then also add a fade in and fade out PNG.

  I have the current command which works perfectly in merging two video files one on top of the other.

  ffmpeg -y -i output.mp4 -i transparent.mp4 -filter_complex "[1:v][0:v]scale2ref[ua][b];[ua]setsar=1,format=yuva444p,colorchannelmixer=aa=.7[u];[b][u]overlay=eof_action=pass[v]" -map [v] awsome.mp4

  I need to now add a PNG on it as well that fades in at 1s and fades out at 9.5s.

  Appreciate any and all advice.