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• How to label outputs inside the ffmpeg's process of transcoding for use them in mapping and in tee muxer ?

  20 juillet 2022, par youni

  I have a video, that consists of video stream and audio stream. I trancode it into two videos : 1920x1080 and 1280x720 with the same audio stream. I do not wish to transcode audio stream two times, I wish to use it twice with ffmpeg '-f tee' option. Now I need your support.

  


  This does not work :

  


  ffmpeg -to 00:00:10 -i /v \
  -map 0:v -an -vcodec libx264 -s 1920x1080 -b:v 4000k [VIDEO]\
  -map 0:v -an -vcodec libx264 -s 1280x720 -b:v 2000k [VIDEO2]\
  -f tee \
    -map [VIDEO] -map [VIDEO2] -map 0:a \
      -c:a mp3 -ab 42k \
        "[select='0,2':f=flv]1.mp4|[select='1,2':f=flv]2.mp4"
[NULL @ 0x55b7e2709340] Unable to find a suitable output format for '[VIDEO]'
[VIDEO]: Invalid argument


  


  My logic here was to label each output after -vcodec.. options and use these two labels in mapping and in tee muxer. Could you, please, advise what to do here ?

  


  This also does not work :

  


  ffmpeg -to 00:00:10 -i /v \
  -c:a mp3 -ab 42k \
    -filter_complex '[0:a]acopy[AUDIO];[0:a]acopy[AUDIO2]' \
  -map v -map [AUDIO] -vcodec libx264 -s 1920x1080 -b:v 4000k -f flv 1.mp4 \
  -map v -map [AUDIO2] -vcodec libx264 -s 1280x720 -b:v 2000k -f flv 2.mp4
ffprobe 1.mp4
ffprobe 2.mp4
  1.mp4: Stream #0:1: Audio: mp3, 48000 Hz, stereo, fltp, 42 kb/s
  2.mp4: Stream #0:1: Audio: mp3, 48000 Hz, stereo, fltp, 128 kb/s


  


  The result file 2.mp4 has default audio settings : 128 kb/s instead of 42 kb/s.

  


  My workable variant gives exactly correct result, but the process of transcoding is not optimized :

  


  ffmpeg -to 00:00:10 -i /v \
  -c:a mp3 -ab 42k -vcodec libx264 -s 1920x1080 -b:v 4000k -f flv 1.mp4 \
  -c:a mp3 -ab 42k -vcodec libx264 -s 1280x720 -b:v 2000k -f flv 2.mp4


  


  In this process ffmpeg transcodes audio stream twice, as I think. But I need to optimize this process and transcode audio stream once and use it twice with tee muxer. Could you say me, how to label outputs correctly as in my first code for use them in -map ?

  


• Concatenate multiple videos with a black screen interval into one video

  21 mars 2016, par AHC

  I am using ffmpeg to join a bunch of videos together.
  I am using the classic join ffmpeg code :
  

  ffmpeg -f concat -i joinlist.txt -c copy joinedfile.mp4

  but the problem is that the videos are of different formats, encodings, but the same size : all 640x480. I want to join them all and put a black screen video with no sound every other video :

  video1 + black_screen_video + video2 + black_screen_video + video3 ...

  I generated a black screen video of 2 seconds duration using :

  ffmpeg -f lavfi -i color=c=black:s=640x480:d=2 black_screen_video.mp4

  so all of the videos are of the same size : 640x480, and 25 fps but different codecs. The videos have sound, except for the black screen video.
  I can’t do anything manual, because the number of videos are around several hundred. So it has got to be an automatic way to do all this.

  When I joined them together using the above code, the resulting video does not play correctly at all.

  I know that I have to re-encode them, but how to do this to all these videos at once, with one line of code ?

  Update :
  I am already using with success this code to join them together, but only three, if I have more than one hundred, it is time consuming to write down one by one :

  ffmpeg -i vid1.avi -i vid2.avi -i vid3.avi -filter_complex "[0:v:0] [0:a:0] [1:v:0] [1:a:0] [2:v:0] [2:a:0] concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4

  but this is joining only the videos, not looping the black screen video. When I do with black screen, ffmpeg gives me stream matching errors.

• ffmpeg how to remove black borders when resizing an image

  3 juin 2021, par Mapg

  I am creating some thumbnails using FFmpeg and I see that some black borders are created when I resize them.

  


  I guess this is happening because the video source dimension doesn't match exactly the target dimension, so FFmpeg fills out the blank space with this black color.

  


  My question is ...

  


  Can I change this "black color" used by FFmpeg by default so I can match these extra borders added with the background of my application ?

  


  If this is not possible ...

  


  Can I convert these black borders to a transparent area so I can create a PNG to match my background which has a different color (a kind of light green)

  


  I have attached an example where you will see two black pixels height in the bottom zone of the picture.

  


  This is what I want to convert to transparent or being able to choose my own color.

  


  Any idea to solve this issue will be very helpful for me ?

  


  Thank you very much in advance !

  


  Mapg