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• ffmpeg - when scaling, how to keep shapes of people's heads

  19 janvier 2017, par Dave

  Ok, I’m quite familiar with FFMPEG utility in general, and have used it for
  years to cut short snippets from videos, etc. But it’s only in the last
  month that and I decided to learn to use it to transcode with video-filters
  etc. (Before that, I was using other tools such as ’Handbrake’ and ’FreeMake’
  and VLC, etc.)

  For my ffmpeg transcodes, my target output resolution will always be constant, from one transcode run to the next. But the resolution and display aspect-ratio of the input file, from one transcode run to the next, will vary...could be almost any values.
  The input files will never already have black-bars when displayed.

  So, the relevant portion [ i.e. the video-filter(s) part) of my cmd line ] presently is as follows :

  ffmpeg ... -vf "scale=720:406,setsar=1,pad=720:506:0:40:Black" ...

  Also note : I do NOT use the "-aspect" option in the cmd-line. (Maybe I’ll
  need to (???) to solve my issue, but I’m unsure about how that interacts
  with scaling.)

  ( EDIT : Oh, I happen to have chosen that resolution value of 720x406, for
  the image-area (i.e. inside the top/bottom black bars) because it
  has an aspect ratio of 16:9 (Of course, 16:9 ratio is common these days. )

  My cmd always executes cleanly and produces an output file (a WebM, tho I doubt
  that container types and/or vcodec choices matter at all to scaling algorithm issues).

  So the issue/problem that I’m trying to solve is how to prevent any stretching
  in either direction. In other words, a round soccer ball in the input file
  must yield a round ball in the output file ! (NOT oval-shaped in either axis).

  ( Edit #2 : Oh, I forgot to mention that I’m not have the same amount of stretching from one ffmpeg output file to the next. Sometimes there is
  no stretch in my output file, and with some other input file, the
  people are too tall in the output, and some other output file will have
  people are too wide. I’m assuming
  there is some single cmd that will always work for each randomly sized
  input file, WITHOUT having to resort to examining meta-data of each
  input and then having to adjust portions of the needed ffmpeg cmd.
  I assume this because I have used a tool called "FreeMake" that needs
  no such adjustment. When you do a ’scale’ with that program, it asks
  you to choose one of four adjustment-algorithms labeled "original"
  "stretched", "zoom..." and "auto". If I recall correctly, it was the
  "auto" choice that prevented any stretching.)

  The goal of that last filter (i.e. the "pad=720:506:0:40:Black" phrase) is to
  add a black bar of 40 pixels to the top and 60 pixels to the bottom.
  (That filter IS producing the black-bands, as desired. I mention it,
  because I’m unsure whether it could be having any effect on the altered
  shape of the ’round soccer ball’). If the "pad" filter IS part of the
  issue, then maybe I’ll need to make multiple ffmpeg cmds to achieve
  my overall goal (!?!?). [I’d LIKE to be able to do everything in just
  one ffmpeg cmd, as shown.]

  OK ?

  So are there any image-processing and ffmpeg gurus out there that
  know how to fix my problem ?

  TIA...

  Dave

• ffmpeg :How to make Text_1 ( bold ) and Text_2 ( Normal ) ?

  15 décembre 2016, par Bheem Swami

  ffmpeg -i raw_video.mp4 -i photo1.png -i photo2.png -filter_complex "[0:v]drawtext=fontfile=aller_Bd.ttf:text='Text_1':fontcolor=black@1.0:fontsize=18:x=20:y=259,drawtext=fontfile=aller_Rg.ttf:text='Text_2':fontcolor=black@1.0:fontsize=16:x=67:y=259[text];[text][1:v]overlay=215:0 [tmp]; [tmp] overlay=372:216" -codec:v libx264 -codec:a copy -y output_video.mp4

  Add 2 text : Text_1 and Text_2

  1. How to make Text_1 ( bold ) and Text_2 ( Normal )
  2. Text_1 is dynamic (not fix length) . How to start Text_2 after Text_1

• Extract part of a video using ffmpeg_extract_subclip - get a clip longer than expected

  4 juin 2020, par rightly0716

  I'm trying to extract a part of a video and find the solution on this page very helpful : 
Extract part of a video using ffmpeg_extract_subclip - black frames

  



  The function write_videofile helps get what I need exactly but a bit slow. The ffmpeg_extract_subclip function is indeed very fast, but somehow generates a weird clip that is slightly longer than what I need. For example, if I use the cmd below (no matter with or without -copyinkf),

  



  ffmpeg -y -ss 218.00 -i input.mp4 -t 7.00 -vcodec copy -acodec copy output.mp4


  



  My output.mp4 will be 9 second long, with the last two seconds frozen with no audio. Anyone saw a similar issue before ? Thanks a lot !